--- uid: web-pages/overview/getting-started/introducing-razor-syntax-vb title: "Introduction to ASP.NET Web Programming Using the Razor Syntax (Visual Basic) | Microsoft Docs" author: tfitzmac description: "This appendix gives you an overview of programming with ASP.NET Web pages in Visual Basic, using the Razor syntax." ms.author: aspnetcontent manager: wpickett ms.date: 02/07/2014 ms.topic: article ms.assetid: 5da59646-e973-41cd-88a9-c6b2c0594027 ms.technology: dotnet-webpages ms.prod: .net-framework msc.legacyurl: /web-pages/overview/getting-started/introducing-razor-syntax-vb msc.type: authoredcontent --- Introduction to ASP.NET Web Programming Using the Razor Syntax (Visual Basic) ==================== by [Tom FitzMacken](https://github.com/tfitzmac) > This article gives you an overview of programming with ASP.NET Web Pages using the Razor syntax and Visual Basic. ASP.NET is Microsoft's technology for running dynamic web pages on web servers. > > **What you'll learn**: > > - The top 8 programming tips for getting started with programming ASP.NET Web Pages using Razor syntax. > - Basic programming concepts you'll need. > - What ASP.NET server code and the Razor syntax is all about. > > > ## Software versions > > > - ASP.NET Web Pages (Razor) 3 > > > This tutorial also works with ASP.NET Web Pages 2. Most examples of using ASP.NET Web Pages with Razor syntax use C#. But the Razor syntax also supports Visual Basic. To program an ASP.NET web page in Visual Basic, you create a web page with a *.vbhtml* filename extension, and then add Visual Basic code. This article gives you an overview of working with the Visual Basic language and syntax to create ASP.NET Webpages. > [!NOTE] > The default website templates for Microsoft WebMatrix (**Bakery**, **Photo Gallery**, and **Starter Site**, etc.) are available in C# and Visual Basic versions. You can install the Visual Basic templates by as NuGet packages. Website templates are installed in the root folder of your site in a folder named *Microsoft Templates*. ## The Top 8 Programming Tips This section lists a few tips that you absolutely need to know as you start writing ASP.NET server code using the Razor syntax. ### 1. You add code to a page using the @ character The `@` character starts inline expressions, single-statement blocks, and multi-statement blocks: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample1.vbhtml)] The result displayed in a browser: ![Razor-Img1](introducing-razor-syntax-vb/_static/image1.jpg) > [!TIP] > > **HTML Encoding** > > When you display content in a page using the `@` character, as in the preceding examples, ASP.NET HTML-encodes the output. This replaces reserved HTML characters (such as `<` and `>` and `&`) with codes that enable the characters to be displayed as characters in a web page instead of being interpreted as HTML tags or entities. Without HTML encoding, the output from your server code might not display correctly, and could expose a page to security risks. > > If your goal is to output HTML markup that renders tags as markup (for example `

` for a paragraph or `` to emphasize text), see the section [Combining Text, Markup, and Code in Code Blocks](#BM_CombiningTextMarkupAndCode) later in this article. > > You can read more about HTML encoding in [Working with HTML Forms in ASP.NET Web Pages Sites](https://go.microsoft.com/fwlink/?LinkId=202892). ### 2. You enclose code blocks with Code...End Code A code block includes one or more code statements and is enclosed with the keywords `Code` and `End Code`. Place the opening `Code` keyword immediately after the `@` character — there can't be whitespace between them. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample2.vbhtml)] The result displayed in a browser: ![Razor-Img2](introducing-razor-syntax-vb/_static/image2.jpg) ### 3. Inside a block, you end each code statement with a line break In a Visual Basic code block, each statement ends with a line break. (Later in the article you'll see a way to wrap a long code statement into multiple lines if needed.) [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample3.vbhtml)] ### 4. You use variables to store values You can store values in a *variable*, including strings, numbers, and dates, etc. You create a new variable using the `Dim` keyword. You can insert variable values directly in a page using `@`. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample4.vbhtml)] The result displayed in a browser: ![Razor-Img3](introducing-razor-syntax-vb/_static/image3.jpg) ### 5. You enclose literal string values in double quotation marks A *string* is a sequence of characters that are treated as text. To specify a string, you enclose it in double quotation marks: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample5.vbhtml)] To embed double quotation marks within a string value, insert two double quotation mark characters. If you want the double quotation character to appear once in the page output, enter it as `""` within the quoted string, and if you want it to appear twice, enter it as `""""` within the quoted string. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample6.vbhtml)] The result displayed in a browser: ![Razor-Img4](introducing-razor-syntax-vb/_static/image4.jpg) ### 6. Visual Basic code is not case sensitive The Visual Basic language is not case sensitive. Programming keywords (like `Dim`, `If`, and `True`) and variable names (like `myString`, or `subTotal`) can be written in any case. The following lines of code assign a value to the variable `lastname` using a lowercase name, and then output the variable value to the page using an uppercase name. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample7.vbhtml)] The result displayed in a browser: ![vb-syntax-5](introducing-razor-syntax-vb/_static/image5.jpg) ### 7. Much of your coding involves working with objects An object represents a thing that you can program with — a page, a text box, a file, an image, a web request, an email message, a customer record (database row), etc. Objects have properties that describe their characteristics — a text box object has a `Text` property, a request object has a `Url` property, an email message has a `From` property, and a customer object has a `FirstName` property. Objects also have methods that are the "verbs" they can perform. Examples include a file object's `Save` method, an image object's `Rotate` method, and an email object's `Send` method. You'll often work with the `Request` object, which gives you information like the values of form fields on the page (text boxes, etc.), what type of browser made the request, the URL of the page, the user identity, etc. This example shows how to access properties of the `Request` object and how to call the `MapPath` method of the `Request` object, which gives you the absolute path of the page on the server: [!code-html[Main](introducing-razor-syntax-vb/samples/sample8.html)] The result displayed in a browser: ![Razor-Img5](introducing-razor-syntax-vb/_static/image6.jpg) ### 8. You can write code that makes decisions A key feature of dynamic web pages is that you can determine what to do based on conditions. The most common way to do this is with the `If` statement (and optional `Else` statement). [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample9.vbhtml)] The statement `If IsPost` is a shorthand way of writing `If IsPost = True`. Along with `If` statements, there are a variety of ways to test conditions, repeat blocks of code, and so on, which are described later in this article. The result displayed in a browser (after clicking **Submit**): ![Razor-Img6](introducing-razor-syntax-vb/_static/image7.jpg) > [!TIP] > > **HTTP GET and POST Methods and the IsPost Property** > > The protocol used for web pages (HTTP) supports a very limited number of methods ("verbs") that are used to make requests to the server. The two most common ones are GET, which is used to read a page, and POST, which is used to submit a page. In general, the first time a user requests a page, the page is requested using GET. If the user fills in a form and then clicks **Submit**, the browser makes a POST request to the server. > > In web programming, it's often useful to know whether a page is being requested as a GET or as a POST so that you know how to process the page. In ASP.NET Web Pages, you can use the `IsPost` property to see whether a request is a GET or a POST. If the request is a POST, the `IsPost` property will return true, and you can do things like read the values of text boxes on a form. Many examples you'll see show you how to process the page differently depending on the value of `IsPost`. ## A Simple Code Example This procedure shows you how to create a page that illustrates basic programming techniques. In the example, you create a page that lets users enter two numbers, then it adds them and displays the result. 1. In your editor, create a new file and name it *AddNumbers.vbhtml*. 2. Copy the following code and markup into the page, replacing anything already in the page. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample10.vbhtml)] Here are some things for you to note: - The `@` character starts the first block of code in the page, and it precedes the `totalMessage` variable embedded near the bottom. - The block at the top of the page is enclosed in `Code...End Code`. - The variables `total`, `num1`, `num2`, and `totalMessage` store several numbers and a string. - The literal string value assigned to the `totalMessage` variable is in double quotation marks. - Because Visual Basic code is not case sensitive, when the `totalMessage` variable is used near the bottom of the page, its name only needs to match the spelling of the variable declaration at the top of the page. The casing doesn't matter. - The expression `num1.AsInt()` + `num2.AsInt()` shows how to work with objects and methods. The `AsInt` method on each variable converts the string entered by a user to a whole number (an integer) that can be added. - The `
` tag includes a `method="post"` attribute. This specifies that when the user clicks **Add**, the page will be sent to the server using the HTTP POST method. When the page is submitted, the code `If IsPost` evaluates to true and the conditional code runs, displaying the result of adding the numbers. 3. Save the page and run it in a browser. (Make sure the page is selected in the **Files** workspace before you run it.) Enter two whole numbers and then click the **Add** button. ![Razor-Img7](introducing-razor-syntax-vb/_static/image8.jpg) ## Visual Basic Language and Syntax Earlier you saw a basic example of how to create an ASP.NET web page, and how you can add server code to HTML markup. Here you'll learn the basics of using Visual Basic to write ASP.NET server code using the Razor syntax — that is, the programming language rules. If you're experienced with programming (especially if you've used C, C++, C#, Visual Basic, or JavaScript), much of what you read here will be familiar. You'll probably need to familiarize yourself only with how WebMatrix code is added to markup in *.vbhtml* files. ### Combining text, markup, and code in code blocks In server code blocks, you'll often want to output text and markup to the page. If a server code block contains text that's not code and that instead should be rendered as is, ASP.NET needs to be able to distinguish that text from code. There are several ways to do this. - Enclose the text in an HTML block element like `

` or ``: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample11.vbhtml)] The HTML element can include text, additional HTML elements, and server-code expressions. When ASP.NET sees the opening HTML tag (for example, `

`), it renders everything the element and its content as is to the browser (and resolves the server-code expressions). - Use the `@:` operator or the `` element. The `@:` outputs a single line of content containing plain text or unmatched HTML tags; the `` element encloses multiple lines to output. These options are useful when you don't want to render an HTML element as part of the output. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample12.vbhtml)] The following example repeats the previous example but uses a single pair of `` tags to enclose the text to render. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample13.vbhtml)] In the following example, the `` and `` tags enclose three lines, all of which have some uncontained text and unmatched HTML tags (`
`), along with server code and matched HTML tags. Again, you could also precede each line individually with the `@:` operator; either way works. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample14.vbhtml)] > [!NOTE] > When you output text as shown in this section — using an HTML element, the `@:` operator, or the `` element — ASP.NET doesn't HTML-encode the output. (As noted earlier, ASP.NET does encode the output of server code expressions and server code blocks that are preceded by `@`, except in the special cases noted in this section.) ### Whitespace Extra spaces in a statement (and outside of a string literal) don't affect the statement: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample15.vbhtml)] ### Breaking long statements into multiple lines You can break a long code statement into multiple lines by using the underscore character `_` (which in Visual Basic is called the *continuation character*) after each line of code. To break a statement onto the next line, at the end of the line add a space and then the continuation character. Continue the statement on the next line. You can wrap statements onto as many lines as you need to improve readability. The following statements are the same: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample16.vbhtml)] However, you can't wrap a line in the middle of a string literal. The following example doesn't work: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample17.vbhtml)] To combine a long string that wraps to multiple lines like the above code, you would need to use the *concatenation operator* (`&`), which you'll see later in this article. ### Code comments Comments let you leave notes for yourself or others. Razor syntax comments are prefixed with `@*` and end with `*@`. [!code-cshtml[Main](introducing-razor-syntax-vb/samples/sample18.cshtml)] Within code blocks you can use the Razor syntax comments, or you can use ordinary Visual Basic comment character, which is a single quote (`'`) prefixed to each line. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample19.vbhtml)] ## Variables A variable is a named object that you use to store data. You can name variables anything, but the name must begin with an alphabetic character and it cannot contain whitespace or reserved characters. In Visual Basic, as you saw earlier, the case of the letters in a variable name doesn't matter. ### Variables and data types A variable can have a specific data type, which indicates what kind of data is stored in the variable. You can have string variables that store string values (like "Hello world"), integer variables that store whole-number values (like 3 or 79), and date variables that store date values in a variety of formats (like 4/12/2012 or March 2009). And there are many other data types you can use. However, you don't have to specify a type for a variable. In most cases ASP.NET can figure out the type based on how the data in the variable is being used. (Occasionally you must specify a type; you'll see examples where this is true.) To declare a variable without specifying a type, use `Dim` plus the variable name (for instance, `Dim myVar`). To declare a variable with a type, use `Dim` plus the variable name, followed by `As` and then the type name (for instance, `Dim myVar As String`). [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample20.vbhtml)] The following example shows some inline expressions that use the variables in a web page. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample21.vbhtml)] The result displayed in a browser: ![Razor-Img9](introducing-razor-syntax-vb/_static/image9.jpg) ### Converting and testing data types Although ASP.NET can usually determine a data type automatically, sometimes it can't. Therefore, you might need to help ASP.NET out by performing an explicit conversion. Even if you don't have to convert types, sometimes it's helpful to test to see what type of data you might be working with. The most common case is that you have to convert a string to another type, such as to an integer or date. The following example shows a typical case where you must convert a string to a number. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample22.vbhtml)] As a rule, user input comes to you as strings. Even if you've prompted the user to enter a number, and even if they've entered a digit, when user input is submitted and you read it in code, the data is in string format. Therefore, you must convert the string to a number. In the example, if you try to perform arithmetic on the values without converting them, the following error results, because ASP.NET cannot add two strings: `Cannot implicitly convert type 'string' to 'int'.` To convert the values to integers, you call the `AsInt` method. If the conversion is successful, you can then add the numbers. The following table lists some common conversion and test methods for variables. | **Method** | **Description** | **Example** | | --- | --- | --- | | `AsInt(), IsInt()` | Converts a string that represents a whole number (like "593") to an integer. | [!code-vb[Main](introducing-razor-syntax-vb/samples/sample23.vb)] | | `AsBool(), IsBool()` | Converts a string like "true" or "false" to a Boolean type. | [!code-vb[Main](introducing-razor-syntax-vb/samples/sample24.vb)] | | `AsFloat(), IsFloat()` | Converts a string that has a decimal value like "1.3" or "7.439" to a floating-point number. | [!code-vb[Main](introducing-razor-syntax-vb/samples/sample25.vb)] | | `AsDecimal(), IsDecimal()` | Converts a string that has a decimal value like "1.3" or "7.439" to a decimal number. (In ASP.NET, a decimal number is more precise than a floating-point number.) | [!code-vb[Main](introducing-razor-syntax-vb/samples/sample26.vb)] | | `AsDateTime(), IsDateTime()` | Converts a string that represents a date and time value to the ASP.NET `DateTime` type. | [!code-vb[Main](introducing-razor-syntax-vb/samples/sample27.vb)] | | `ToString()` | Converts any other data type to a string. | [!code-vb[Main](introducing-razor-syntax-vb/samples/sample28.vb)] | ## Operators An operator is a keyword or character that tells ASP.NET what kind of command to perform in an expression. Visual Basic supports many operators, but you only need to recognize a few to get started developing ASP.NET web pages. The following table summarizes the most common operators. | **Operator** | **Description** | **Examples** | | --- | --- | --- | | `+ - * /` | Math operators used in numerical expressions. | [!code-vb[Main](introducing-razor-syntax-vb/samples/sample29.vb)] | | `=` | Assignment and equality. Depending on context, either assigns the value on the right side of a statement to the object on the left side, or checks the values for equality. | [!code-vb[Main](introducing-razor-syntax-vb/samples/sample30.vb)] | | `<>` | Inequality. Returns `True` if the values are not equal. | [!code-vb[Main](introducing-razor-syntax-vb/samples/sample31.vb)] | | `< > <= >=` | Less than, greater than, less than or equal, and greater than or equal. | [!code-vb[Main](introducing-razor-syntax-vb/samples/sample32.vb)] | | `&` | Concatenation, which is used to join strings. | [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample33.vbhtml)] | | `+= -=` | The increment and decrement operators, which add and subtract 1 (respectively) from a variable. | [!code-vb[Main](introducing-razor-syntax-vb/samples/sample34.vb)] | | `.` | Dot. Used to distinguish objects and their properties and methods. | [!code-vb[Main](introducing-razor-syntax-vb/samples/sample35.vb)] | | `()` | Parentheses. Used to group expressions, to pass parameters to methods, and to access members of arrays and collections. | [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample36.vbhtml)] | | `Not` | Not. Reverses a true value to false and vice versa. Typically used as a shorthand way to test for `False` (that is, for not `True`). | [!code-vb[Main](introducing-razor-syntax-vb/samples/sample37.vb)] | | `AndAlso OrElse` | Logical AND and OR, which are used to link conditions together. | [!code-vb[Main](introducing-razor-syntax-vb/samples/sample38.vb)] | ## Working with File and Folder Paths in Code You'll often work with file and folder paths in your code. Here is an example of physical folder structure for a website as it might appear on your development computer: `C:\WebSites\MyWebSite default.cshtml datafile.txt \images Logo.jpg \styles Styles.css` Here are some essential details about URLs and paths: - A URL begins with either a domain name (`http://www.example.com`) or a server name (`http://localhost`, `http://mycomputer`). - A URL corresponds to a physical path on a host computer. For example, `http://myserver` might correspond to the folder *C:\websites\mywebsite* on the server. - A virtual path is shorthand to represent paths in code without having to specify the full path. It includes the portion of a URL that follows the domain or server name. When you use virtual paths, you can move your code to a different domain or server without having to update the paths. Here's an example to help you understand the differences: | Complete URL | `http://mycompanyserver/humanresources/CompanyPolicy.htm` | | --- | --- | | Server name | *mycompanyserver* | | Virtual path | */humanresources/CompanyPolicy.htm* | | Physical path | *C:\mywebsites\humanresources\CompanyPolicy.htm* | The virtual root is /, just like the root of your C: drive is \. (Virtual folder paths always use forward slashes.) The virtual path of a folder doesn't have to have the same name as the physical folder; it can be an alias. (On production servers, the virtual path rarely matches an exact physical path.) When you work with files and folders in code, sometimes you need to reference the physical path and sometimes a virtual path, depending on what objects you're working with. ASP.NET gives you these tools for working with file and folder paths in code: the `Server.MapPath` method, and the `~` operator and `Href` method. ### Converting virtual to physical paths: the Server.MapPath method The `Server.MapPath` method converts a virtual path (like */default.cshtml*) to an absolute physical path (like *C:\WebSites\MyWebSiteFolder\default.cshtml*). You use this method any time you need a complete physical path. A typical example is when you're reading or writing a text file or image file on the web server. You typically don't know the absolute physical path of your site on a hosting site's server, so this method can convert the path you do know — the virtual path — to the corresponding path on the server for you. You pass the virtual path to a file or folder to the method, and it returns the physical path: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample39.vbhtml)] ### Referencing the virtual root: the ~ operator and Href method In a *.cshtml* or *.vbhtml* file, you can reference the virtual root path using the `~` operator. This is very handy because you can move pages around in a site, and any links they contain to other pages won't be broken. It's also handy in case you ever move your website to a different location. Here are some examples: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample40.vbhtml)] If the website is `http://myserver/myapp`, here's how ASP.NET will treat these paths when the page runs: - `myImagesFolder`: `http://myserver/myapp/images` - `myStyleSheet` : `http://myserver/myapp/styles/Stylesheet.css` (You won't actually see these paths as the values of the variable, but ASP.NET will treat the paths as if that's what they were.) You can use the `~` operator both in server code (as above) and in markup, like this: [!code-html[Main](introducing-razor-syntax-vb/samples/sample41.html)] In markup, you use the `~` operator to create paths to resources like image files, other web pages, and CSS files. When the page runs, ASP.NET looks through the page (both code and markup) and resolves all the `~` references to the appropriate path. ## Conditional Logic and Loops ASP.NET server code lets you perform tasks based on conditions and write code that repeats statements a specific number of times that is, code that runs a loop). ### Testing conditions To test a simple condition you use the `If...Then` statement, which returns `True` or `False` based on a test you specify: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample42.vbhtml)] The `If` keyword starts a block. The actual test (condition) follows the `If` keyword and returns true or false. The `If` statement ends with `Then`. The statements that will run if the test is true are enclosed by `If` and `End If`. An `If` statement can include an `Else` block that specifies statements to run if the condition is false: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample43.vbhtml)] If an `If` statement starts a code block, you don't have to use the normal `Code...End Code` statements to include the blocks. You can just add `@` to the block, and it will work. This approach works with `If` as well as other Visual Basic programming keywords that are followed by code blocks, including `For`, `For Each`, `Do While`, etc. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample44.vbhtml)] You can add multiple conditions using one or more `ElseIf` blocks: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample45.vbhtml)] In this example, if the first condition in the `If` block is not true, the `ElseIf` condition is checked. If that condition is met, the statements in the `ElseIf` block are executed. If none of the conditions are met, the statements in the `Else` block are executed. You can add any number of `ElseIf` blocks, and then close with an `Else` block as the "everything else" condition. To test a large number of conditions, use a `Select Case` block: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample46.vbhtml)] The value to test is in parentheses (in the example, the weekday variable). Each individual test uses a `Case` statement that lists a value. If the value of a `Case` statement matches the test value, the code in that `Case` block is executed. The result of the last two conditional blocks displayed in a browser: ![Razor-Img10](introducing-razor-syntax-vb/_static/image10.jpg) ### Looping code You often need to run the same statements repeatedly. You do this by looping. For example, you often run the same statements for each item in a collection of data. If you know exactly how many times you want to loop, you can use a `For` loop. This kind of loop is especially useful for counting up or counting down: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample47.vbhtml)] The loop begins with the `For` keyword, followed by three elements: - Immediately after the `For` statement, you declare a counter variable (you don't have to use `Dim`) and then indicate the range, as in `i = 10 to 20`. This means the variable `i` will start counting at 10 and continue until it reaches 20 (inclusive). - Between the `For` and `Next` statements is the content of the block. This can contain one or more code statements that execute with each loop. - The `Next i` statement ends the loop. It increments the counter and starts the next iteration of the loop. The line of code between the `For` and `Next` lines contains the code that runs for each iteration of the loop. The markup creates a new paragraph (`

` element) each time and adds a line to the output, displaying the value of i (the counter). When you run this page, the example creates 11 lines displaying the output, with the text in each line indicating the item number. ![Razor-Img11](introducing-razor-syntax-vb/_static/image11.jpg) If you're working with a collection or array, you often use a `For Each` loop. A collection is a group of similar objects, and the `For Each` loop lets you carry out a task on each item in the collection. This type of loop is convenient for collections, because unlike a `For` loop, you don't have to increment the counter or set a limit. Instead, the `For Each` loop code simply proceeds through the collection until it's finished. This example returns the items in the `Request.ServerVariables` collection (which contains information about your web server). It uses a `For Each` loop to display the name of each item by creating a new `

  • ` element in an HTML bulleted list. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample48.vbhtml)] The `For Each` keyword is followed by a variable that represents a single item in the collection (in the example, `myItem`), followed by the `In` keyword, followed by the collection you want to loop through. In the body of the `For Each` loop, you can access the current item using the variable that you declared earlier. ![Razor-Img12](introducing-razor-syntax-vb/_static/image12.jpg) To create a more general-purpose loop, use the `Do While` statement: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample49.vbhtml)] This loop begins with the `Do While` keyword, followed by a condition, followed by the block to repeat. Loops typically increment (add to) or decrement (subtract from) a variable or object used for counting. In the example, the `+=` operator adds 1 to the value of a variable each time the loop runs. (To decrement a variable in a loop that counts down, you would use the decrement operator `-=`.) ## Objects and Collections Nearly everything in an ASP.NET website is an object, including the web page itself. This section discusses some important objects you'll work with frequently in your code. ### Page objects The most basic object in ASP.NET is the page. You can access properties of the page object directly without any qualifying object. The following code gets the page's file path, using the `Request` object of the page: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample50.vbhtml)] You can use properties of the `Page` object to get a lot of information, such as: - `Request`. As you've already seen, this is a collection of information about the current request, including what type of browser made the request, the URL of the page, the user identity, etc. - `Response`. This is a collection of information about the response (page) that will be sent to the browser when the server code has finished running. For example, you can use this property to write information into the response. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample51.vbhtml)] ### Collection objects (arrays and dictionaries) A collection is a group of objects of the same type, such as a collection of `Customer` objects from a database. ASP.NET contains many built-in collections, like the `Request.Files` collection. You'll often work with data in collections. Two common collection types are the *array* and the *dictionary*. An array is useful when you want to store a collection of similar items but don't want to create a separate variable to hold each item: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample52.vbhtml)] With arrays, you declare a specific data type, such as `String`, `Integer`, or `DateTime`. To indicate that the variable can contain an array, you add parentheses to the variable name in the declaration (such as `Dim myVar() As String`). You can access items in an array using their position (index) or by using the `For Each` statement. Array indexes are zero-based — that is, the first item is at position 0, the second item is at position 1, and so on. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample53.vbhtml)] You can determine the number of items in an array by getting its `Length` property. To get the position of a specific item in the array (that is, to search the array), use the `Array.IndexOf` method. You can also do things like reverse the contents of an array (the `Array.Reverse` method) or sort the contents (the `Array.Sort` method). The output of the string array code displayed in a browser: ![Razor-Img13](introducing-razor-syntax-vb/_static/image13.jpg) A dictionary is a collection of key/value pairs, where you provide the key (or name) to set or retrieve the corresponding value: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample54.vbhtml)] To create a dictionary, you use the `New` keyword to indicate that you're creating a new `Dictionary` object. You can assign a dictionary to a variable using the `Dim` keyword. You indicate the data types of the items in the dictionary using parentheses ( `( )` ). At the end of the declaration, you must add another pair of parentheses, because this is actually a method that creates a new dictionary. To add items to the dictionary, you can call the `Add` method of the dictionary variable (`myScores` in this case), and then specify a key and a value. Alternatively, you can use parentheses to indicate the key and do a simple assignment, as in the following example: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample55.vbhtml)] To get a value from the dictionary, you specify the key in parentheses: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample56.vbhtml)] ## Calling Methods with Parameters As you saw earlier in this article, the objects that you program with have methods. For example, a `Database` object might have a `Database.Connect` method. Many methods also have one or more parameters. A *parameter* is a value that you pass to a method to enable the method to complete its task. For example, look at a declaration for the `Request.MapPath` method, which takes three parameters: [!code-vb[Main](introducing-razor-syntax-vb/samples/sample57.vb)] This method returns the physical path on the server that corresponds to a specified virtual path. The three parameters for the method are `virtualPath`, `baseVirtualDir`, and `allowCrossAppMapping`. (Notice that in the declaration, the parameters are listed with the data types of the data that they'll accept.) When you call this method, you must supply values for all three parameters. When you're using Visual Basic with the Razor syntax, you have two options for passing parameters to a method: *positional parameters* or *named parameters*. To call a method using positional parameters, you pass the parameters in a strict order that's specified in the method declaration. (You would typically know this order by reading documentation for the method.) You must follow the order, and you can't skip any of the parameters — if necessary, you pass an empty string (`""`) or null for a positional parameter that you don't have a value for. The following example assumes you have a folder named *scripts* on your website. The code calls the `Request.MapPath` method and passes values for the three parameters in the correct order. It then displays the resulting mapped path. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample58.vbhtml)] When there are many parameters for a method, you can keep your code cleaner and more readable by using named parameters. To call a method using named parameters, specify the parameter name followed by `:=` and then provide the value. An advantage of named parameters is that you can add them in any order you want. (A disadvantage is that the method call is not as compact.) The following example calls the same method as above, but uses named parameters to supply the values: [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample59.vbhtml)] As you can see, the parameters are passed in a different order. However, if you run the previous example and this example, they'll return the same value. ## Handling Errors ### Try-Catch statements You'll often have statements in your code that might fail for reasons outside your control. For example: - If your code tries to open, create, read, or write a file, all sorts of errors might occur. The file you want might not exist, it might be locked, the code might not have permissions, and so on. - Similarly, if your code tries to update records in a database, there can be permissions issues, the connection to the database might be dropped, the data to save might be invalid, and so on. In programming terms, these situations are called *exceptions*. If your code encounters an exception, it generates (throws) an error message that is, at best, annoying to users. ![Razor-Img14](introducing-razor-syntax-vb/_static/image14.jpg) In situations where your code might encounter exceptions, and in order to avoid error messages of this type, you can use `Try/Catch` statements. In the `Try` statement, you run the code that you're checking. In one or more `Catch` statements, you can look for specific errors (specific types of exceptions) that might have occurred. You can include as many `Catch` statements as you need to look for errors that you're anticipating. > [!NOTE] > We recommend that you avoid using the `Response.Redirect` method in `Try/Catch` statements, because it can cause an exception in your page. The following example shows a page that creates a text file on the first request and then displays a button that lets the user open the file. The example deliberately uses a bad file name so that it will cause an exception. The code includes `Catch` statements for two possible exceptions: `FileNotFoundException`, which occurs if the file name is bad, and `DirectoryNotFoundException`, which occurs if ASP.NET can't even find the folder. (You can uncomment a statement in the example in order to see how it runs when everything works properly.) If your code didn't handle the exception, you would see an error page like the previous screen shot. However, the `Try/Catch` section helps prevent the user from seeing these types of errors. [!code-vbhtml[Main](introducing-razor-syntax-vb/samples/sample60.vbhtml)] ## Additional Resources ### Reference Documentation - [ASP.NET](https://msdn.microsoft.com/en-us/library/ee532866.aspx) - [Visual Basic Language](https://msdn.microsoft.com/en-us/library/2x7h1hfk.aspx)