49 lines
1.9 KiB
Markdown
49 lines
1.9 KiB
Markdown
---
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title: "ASP0006: Do not use non-literal sequence numbers"
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description: "Learn about analysis rule ASP0006: Do not use non-literal sequence numbers"
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author: captainsafia
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monikerRange: '>= aspnetcore-6.0'
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ms.author: riande
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ms.date: 10/21/2021
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no-loc: [".NET MAUI", "Mac Catalyst", "Blazor Hybrid", Home, Privacy, Kestrel, appsettings.json, "ASP.NET Core Identity", cookie, Cookie, Blazor, "Blazor Server", "Blazor WebAssembly", "Identity", "Let's Encrypt", Razor, SignalR]
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uid: diagnostics/asp0006
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---
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# ASP0006: Do not use non-literal sequence numbers
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| **Rule ID** |ASP0006|
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| **Category** |Usage|
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| **Fix is breaking or non-breaking** |Non-breaking|
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## Cause
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An invocation on a method in <xref:Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder> containing a sequence number that isn't a literal as a parameter.
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## Rule description
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Blazor's UI diffing algorithm relies on sequence numbers to determine which elements have changed. Computing the sequence number dynamically or using a counter can result in poor diffing performance. Instead, use a literal sequence number that maps to the source code line for the element. For example, the following code produces an error:
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```csharp
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using Microsoft.AspNetCore.Components.Rendering;
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var builder = new RenderTreeBuilder();
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var seqNum = 1;
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builder.OpenElement(seqNum, ""div"");
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builder.CloseElement();
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```
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## How to fix violations
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To fix a violation of this rule, make sure that calls to methods on the <xref:Microsoft.AspNetCore.Components.Rendering.RenderTreeBuilder> class that take a sequence number as a parameter use a literal sequence number.
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```csharp
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using Microsoft.AspNetCore.Components.Rendering;
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var builder = new RenderTreeBuilder();
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builder.OpenElement(0, ""div"");
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builder.CloseElement();
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```
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## When to suppress warnings
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Do ***not*** suppress a warning from this rule. Using a non-literal sequence number can result in performance degradation.
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