ASP.NET Core Blazor进阶1：高级组件开发
嗨~ 大家好，我是码农刚子。本文将深入探讨Blazor中的高级组件开发技术，包括渲染片段、动态组件、错误边界和虚拟化组件，帮助您构建更强大、更灵活的Blazor应用。1. 渲染片段（RenderFragment）
1.1 基本概念
RenderFragment是Blazor中用于动态渲染UI内容的核心概念，它允许组件接收并渲染来自父组件的标记内容。
1.2 基础用法
@Title
@ChildContent
@FooterContent
@code {
public string Title { get; set; } = "Default Title";
public RenderFragment? ChildContent { get; set; }
public RenderFragment? FooterContent { get; set; }
}@page "/advanced/component"
<ChildComponent Title="高级组件示例">
<ChildContent>
<p>这是主体内容区域</p>
<button >点击我</button>
</ChildContent>
<FooterContent>
<small >这是底部内容</small>
</FooterContent>
</ChildComponent>
1.3 带参数的RenderFragment
<h3>@Title</h3>
@foreach (var item in Items)
{
@ItemTemplate(item)
}
@code {
public string Title { get; set; } = "数据列表";
public IEnumerable<object>? Items { get; set; }
public RenderFragment<object>? ItemTemplate { get; set; }
}@page "/advanced/component/datalist"
@using System.ComponentModel.DataAnnotations
<DataListComponent Title="用户列表"
Items="users">
<ItemTemplate>
@((context as User)?.Id)
<strong>@((context as User)?.Name)</strong>
@((context as User)?.Email)
</ItemTemplate>
</DataListComponent>
@code {
private List<User> users = new();
protected override void OnInitialized()
{
users = new List<User>
{
new User { Id = 1, Name = "张三", Email = "zhangsan@email.com" },
new User { Id = 2, Name = "李四", Email = "lisi@email.com" },
new User { Id = 3, Name = "王五", Email = "wangwu@email.com" }
};
}
public class User
{
public int Id { get; set; }
public string Name { get; set; } = string.Empty;
public string Email { get; set; } = string.Empty;
}
}
2. 动态组件
2.1 使用RenderTreeBuilder动态构建组件
@using Microsoft.AspNetCore.Components.Rendering
@foreach (var componentType in ComponentTypes)
{
@{
var index = ComponentTypes.IndexOf(componentType);
BuildComponent(index);
}
}
@code {
public List<Type> ComponentTypes { get; set; } = new();
public Dictionary<Type, Dictionary<string, object>> ComponentParameters { get; set; } = new();
private void BuildComponent(int sequence)
{
var componentType = ComponentTypes;
var parameters = ComponentParameters.ContainsKey(componentType)
? ComponentParameters
: new Dictionary<string, object>();
}
protected override void BuildRenderTree(RenderTreeBuilder builder)
{
for (int i = 0; i < ComponentTypes.Count; i++)
{
builder.OpenElement(i * 2, "div");
builder.AddAttribute(i * 2 + 1, "class", "dynamic-component");
builder.OpenComponent(i * 2 + 2, ComponentTypes);
if (ComponentParameters.ContainsKey(ComponentTypes))
{
foreach (var param in ComponentParameters])
{
builder.AddAttribute(i * 2 + 3, param.Key, param.Value);
}
}
builder.CloseComponent();
builder.CloseElement();
}
}
}2.2 动态组件容器
@using Microsoft.AspNetCore.Components
@if (CurrentComponentType != null)
{
<DynamicComponent Type="CurrentComponentType" Parameters="CurrentParameters" />
}
else
{
<p>请选择要显示的组件</p>
}
<button@onclick="() => ShowComponent(typeof(Counter))">
显示计数器
</button>
<button@onclick="() => ShowComponent(typeof(FetchData))">
显示数据获取
</button>
<button@onclick="() => ShowComponent(typeof(TodoList))">
显示待办事项
</button>
@code {
private Type? CurrentComponentType { get; set; }
private Dictionary<string, object> CurrentParameters { get; set; } = new();
private void ShowComponent(Type componentType)
{
CurrentComponentType = componentType;
CurrentParameters = GetParametersForComponent(componentType);
StateHasChanged();
}
private Dictionary<string, object> GetParametersForComponent(Type componentType)
{
var parameters = new Dictionary<string, object>();
if (componentType == typeof(Counter))
{
parameters["IncrementAmount"] = 5;
}
else if (componentType == typeof(TodoList))
{
parameters["Title"] = "动态待办事项";
}
return parameters;
}
}2.3 自定义动态组件选择器
@using Microsoft.AspNetCore.Components
<DynamicComponent
Type="ResolveComponentType()"
Parameters="ResolveParameters()" />
@code {
public string ComponentName { get; set; } = string.Empty;
public Dictionary<string, object>? InputParameters { get; set; }
public EventCallback<Dictionary<string, object>> OnParametersResolved { get; set; }
private Type ResolveComponentType()
{
return ComponentName switch
{
"Counter" => typeof(Counter),
"TodoList" => typeof(TodoList),
"FetchData" => typeof(FetchData),
"Weather" => typeof(FetchData), // 别名
_ => typeof(NotFoundComponent)
};
}
private Dictionary<string, object> ResolveParameters()
{
var parameters = InputParameters ?? new Dictionary<string, object>();
// 添加默认参数
if (ComponentName == "Counter" && !parameters.ContainsKey("IncrementAmount"))
{
parameters["IncrementAmount"] = 1;
}
// 通知参数解析完成
OnParametersResolved.InvokeAsync(parameters);
return parameters;
}
}3. 错误边界
3.1 基础错误边界组件
@using Microsoft.AspNetCore.Components
<CascadingValue Value="this">
@if (!hasError)
{
@ChildContent
}
else if (ErrorContent != null)
{
@ErrorContent
}
else
{
<h4>出现了错误</h4>
<p>@currentException?.Message</p>
<button@onclick="Recover">
重试
</button>
}
</CascadingValue>
@code {
public RenderFragment? ChildContent { get; set; }
public RenderFragment<Exception>? ErrorContent { get; set; }
public bool RecoverOnRender { get; set; } = true;
private bool hasError;
private Exception? currentException;
public void Recover()
{
hasError = false;
currentException = null;
StateHasChanged();
}
protected override void OnParametersSet()
{
if (RecoverOnRender)
{
hasError = false;
currentException = null;
}
}
public async Task CatchAsync(Func<Task> action)
{
try
{
await action();
hasError = false;
currentException = null;
}
catch (Exception ex)
{
hasError = true;
currentException = ex;
StateHasChanged();
}
}
}3.2 增强型错误边界
@using Microsoft.AspNetCore.Components
@inject ILogger<EnhancedErrorBoundary> Logger
<CascadingValue Value="this">
@if (currentState == ErrorState.Normal)
{
@ChildContent
}
else
{
<i ></i>
<h4>@GetErrorMessage()</h4>
@if (ShowExceptionDetails)
{
<p><strong>错误类型:</strong> @currentException?.GetType().Name</p>
<p><strong>错误信息:</strong> @currentException?.Message</p>
@if (ShowStackTrace)
{
<details>
<summary>堆栈跟踪</summary>
<pre>@currentException?.StackTrace</pre>
</details>
}
}
<button@onclick="Recover">
<i ></i> 重试
</button>
@if (ShowReportButton)
{
<button@onclick="ReportError">
<i ></i> 报告错误
</button>
}
<button@onclick="ToggleDetails">
<i ></i>
@(ShowExceptionDetails ? "隐藏" : "显示")详情
</button>
}
</CascadingValue>
@code {
public RenderFragment? ChildContent { get; set; }
public bool ShowExceptionDetails { get; set; } = false;
public bool ShowStackTrace { get; set; } = false;
public bool ShowReportButton { get; set; } = true;
public EventCallback<Exception> OnError { get; set; }
private ErrorState currentState = ErrorState.Normal;
private Exception? currentException;
private bool ShowExceptionDetailsLocal = false;
protected override async Task OnErrorAsync(Exception exception)
{
currentState = ErrorState.Error;
currentException = exception;
Logger.LogError(exception, "组件渲染时发生错误");
await OnError.InvokeAsync(exception);
await base.OnErrorAsync(exception);
}
private void Recover()
{
currentState = ErrorState.Normal;
currentException = null;
ShowExceptionDetailsLocal = false;
StateHasChanged();
}
private void ReportError()
{
// 这里可以实现错误报告逻辑
Logger.LogError("用户报告错误: {Exception}", currentException);
// 可以发送到错误监控服务
}
private void ToggleDetails()
{
ShowExceptionDetailsLocal = !ShowExceptionDetailsLocal;
}
private string GetErrorContainerClass() => currentState switch
{
ErrorState.Error => "error-container alert alert-danger",
ErrorState.Warning => "error-container alert alert-warning",
_ => "error-container"
};
private string GetErrorIcon() => currentState switch
{
ErrorState.Error => "fas fa-exclamation-triangle",
ErrorState.Warning => "fas fa-exclamation-circle",
_ => "fas fa-info-circle"
};
private string GetErrorMessage() => currentState switch
{
ErrorState.Error => "发生了意外错误",
ErrorState.Warning => "操作未完全成功",
_ => "未知状态"
};
private enum ErrorState
{
Normal,
Warning,
Error
}
}3.3 错误边界使用示例
<h2>错误边界使用示例</h2>
<EnhancedErrorBoundary
ShowExceptionDetails="true"
OnError="OnErrorOccurred">
<h3>安全组件区域</h3>
<UnstableComponent />
<p>这个区域受到错误边界保护</p>
<button@onclick="SafeOperation">
安全操作
</button>
</EnhancedErrorBoundary>
<h3>外部内容（不受错误边界保护）</h3>
<p>这个区域的内容不会受到内部组件错误的影响</p>
@code {
private void OnErrorOccurred(Exception ex)
{
// 处理错误，可以发送到监控系统
Console.WriteLine($"捕获到错误: {ex.Message}");
}
private void SafeOperation()
{
// 安全操作不会抛出异常
}
}4. 虚拟化组件
4.1 基础虚拟化列表
@using Microsoft.AspNetCore.Components.Web.Virtualization
<Virtualize Items="Items" Context="item" OverscanCount="10">
<h5>@item.Name</h5>
<p>@item.Description</p>
<small >ID: @item.Id</small>
</Virtualize>
@code {
public List<DataItem> Items { get; set; } = new();
public class DataItem
{
public int Id { get; set; }
public string Name { get; set; } = string.Empty;
public string Description { get; set; } = string.Empty;
public DateTime CreatedAt { get; set; }
}
}4.2 异步数据虚拟化
@using Microsoft.AspNetCore.Components.Web.Virtualization
<h4>@Title</h4>
显示 <strong>@visibleItemCount</strong> 个项目
(总共 <strong>@totalSize</strong> 个)
<Virtualize ItemsProvider="LoadItems" Context="item"
OverscanCount="5" @ref="virtualizeRef">
#@item.Index
<h6>@item.Name</h6>
<p>@item.Description</p>
@item.Category
<small>@item.CreatedAt.ToString("yyyy-MM-dd HH:mm")</small>
<button
@onclick="() => OnItemClick(item)">
查看
</button>
<Placeholder>
</Placeholder>
</Virtualize>
<button@onclick="RefreshData">
<i ></i> 刷新
</button>
@if (isLoading)
{
<i ></i>
加载中...
}
@code {
public string Title { get; set; } = "虚拟化列表";
public EventCallback<VirtualItem> OnItemClick { get; set; }
private Virtualize<VirtualItem>? virtualizeRef;
private int totalSize = 1000;
private int visibleItemCount;
private bool isLoading;
private async ValueTask<ItemsProviderResult<VirtualItem>> LoadItems(
ItemsProviderRequest request)
{
isLoading = true;
StateHasChanged();
try
{
// 模拟网络延迟
await Task.Delay(100);
var totalItems = await GetTotalItemCountAsync();
var items = await GetItemsAsync(request.StartIndex, request.Count);
visibleItemCount = items.Count;
return new ItemsProviderResult<VirtualItem>(items, totalItems);
}
finally
{
isLoading = false;
StateHasChanged();
}
}
private async Task<int> GetTotalItemCountAsync()
{
// 模拟从API获取总数
await Task.Delay(50);
return totalSize;
}
private async Task<List<VirtualItem>> GetItemsAsync(int startIndex, int count)
{
// 模拟从API获取数据
await Task.Delay(100);
var items = new List<VirtualItem>();
for (int i = 0; i < count && startIndex + i < totalSize; i++)
{
var index = startIndex + i;
items.Add(new VirtualItem
{
Index = index,
Id = Guid.NewGuid(),
Name = $"项目 {index + 1}",
Description = $"这是第 {index + 1} 个项目的描述信息",
Category = GetCategory(index),
CreatedAt = DateTime.Now.AddMinutes(-index),
IsSpecial = index % 7 == 0
});
}
return items;
}
private string GetCategory(int index)
{
var categories = new[] { "技术", "商业", "艺术", "科学", "体育" };
return categories;
}
private async void RefreshData()
{
// 刷新虚拟化组件
if (virtualizeRef != null)
{
await virtualizeRef.RefreshDataAsync();
}
}
public class VirtualItem
{
public int Index { get; set; }
public Guid Id { get; set; }
public string Name { get; set; } = string.Empty;
public string Description { get; set; } = string.Empty;
public string Category { get; set; } = string.Empty;
public DateTime CreatedAt { get; set; }
public bool IsSpecial { get; set; }
}
}4.3 自定义虚拟化网格
@using Microsoft.AspNetCore.Components.Web.Virtualization
<h4>@Title</h4>
<label>
列数:
<input type="number" @bind="columns" @bind:event="oninput"
min="1" max="6"/>
</label>
<label>
项目高度:
<input type="number" @bind="itemHeight" @bind:event="oninput"
min="50" max="300"/>
</label>
<Virtualize ItemsProvider="LoadGridItems" Context="item"
OverscanCount="8" @ref="virtualizeRef">
#@item.Index
@item.Category
<h6 >@item.Title</h6>
<p >@item.Description</p>
<i ></i> @item.Views
<i ></i> @item.Likes
<small >
@item.CreatedAt.ToString("MM/dd/yyyy")
</small>
<button
@onclick="() => OnItemAction(item)">
<i ></i>
</button>
</Virtualize>
@code {
public string Title { get; set; } = "虚拟化网格";
public EventCallback<GridItem> OnItemAction { get; set; }
private Virtualize<GridItem>? virtualizeRef;
private int totalSize = 500;
private int columns = 3;
private int itemHeight = 150;
protected override void OnParametersSet()
{
// 当列数改变时更新网格布局
UpdateGridLayout();
}
private void UpdateGridLayout()
{
// 动态更新CSS网格模板
var style = $@"
.virtualized-grid {{
grid-template-columns: repeat({columns}, 1fr);
}}
";
// 在实际应用中，您可能需要使用JavaScript互操作来动态更新样式
}
private async ValueTask<ItemsProviderResult<GridItem>> LoadGridItems(
ItemsProviderRequest request)
{
// 模拟异步数据加载
await Task.Delay(150);
var totalItems = await GetTotalGridItemCountAsync();
var items = await GetGridItemsAsync(request.StartIndex, request.Count);
return new ItemsProviderResult<GridItem>(items, totalItems);
}
private async Task<int> GetTotalGridItemCountAsync()
{
await Task.Delay(50);
return totalSize;
}
private async Task<List<GridItem>> GetGridItemsAsync(int startIndex, int count)
{
await Task.Delay(100);
var items = new List<GridItem>();
var categories = new[] { "设计", "开发", "营销", "内容", "支持" };
for (int i = 0; i < count && startIndex + i < totalSize; i++)
{
var index = startIndex + i;
var random = new Random(index);
items.Add(new GridItem
{
Index = index,
Id = Guid.NewGuid(),
Title = $"网格项目 {index + 1}",
Description = GenerateDescription(index),
Category = categories,
Views = random.Next(1000, 10000),
Likes = random.Next(10, 500),
CreatedAt = DateTime.Now.AddDays(-random.Next(365)),
IsFeatured = index % 11 == 0
});
}
return items;
}
private string GenerateDescription(int index)
{
var descriptions = new[]
{
"这是一个非常有趣的项目，展示了最新的技术趋势。",
"创新性的解决方案，解决了长期存在的问题。",
"用户友好的设计，提供了出色的用户体验。",
"高性能实现，优化了资源使用和响应时间。",
"跨平台兼容，支持多种设备和浏览器。"
};
return descriptions;
}
public class GridItem
{
public int Index { get; set; }
public Guid Id { get; set; }
public string Title { get; set; } = string.Empty;
public string Description { get; set; } = string.Empty;
public string Category { get; set; } = string.Empty;
public int Views { get; set; }
public int Likes { get; set; }
public DateTime CreatedAt { get; set; }
public bool IsFeatured { get; set; }
}
}总结
本文详细介绍了Blazor中的四个高级组件开发特性：
[*]渲染片段（RenderFragment）：提供了灵活的组件内容注入机制
[*]动态组件：支持运行时组件类型解析和渲染
[*]错误边界：优雅地处理组件树中的异常
[*]虚拟化组件：优化大数据集的性能表现
这些高级特性能够帮助您构建更加健壮、灵活和高性能的Blazor应用程序。在实际开发中，建议根据具体需求选择合适的模式，并注意性能优化和错误处理。
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