165 lines
3.1 KiB
Markdown
165 lines
3.1 KiB
Markdown
# 第八课：异常处理
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## 什么是异常
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异常 = 程序运行时的错误，导致程序无法正常继续。
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```csharp
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int[] numbers = { 1, 2, 3 };
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int x = numbers[10]; // 索引越界 → 抛出 IndexOutOfRangeException
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```
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## try / catch / finally
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```csharp
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try
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{
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// 可能出错的代码放这里
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int[] numbers = { 1, 2, 3 };
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int x = numbers[10];
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}
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catch (Exception ex)
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{
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// 捕获异常并处理
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Console.WriteLine($"出错了: {ex.Message}");
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}
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finally
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{
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// 无论是否出错，都会执行（通常放清理代码）
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Console.WriteLine("无论怎样都会执行");
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}
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```
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## 捕获特定异常类型
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```csharp
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try
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{
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int a = int.Parse("abc"); // 格式错误
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}
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catch (FormatException ex)
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{
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Console.WriteLine("格式错误");
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}
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catch (OverflowException ex)
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{
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Console.WriteLine("数字溢出");
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}
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catch (Exception ex)
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{
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Console.WriteLine($"未知错误: {ex.Message}");
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}
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```
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## 常见异常类型
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| 异常类型 | 触发场景 |
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|----------|----------|
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| `FormatException` | 格式错误（`int.Parse("abc")`） |
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| `NullReferenceException` | 空对象访问（`obj.Method()`，`obj` 为 null） |
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| `IndexOutOfRangeException` | 数组越界 |
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| `FileNotFoundException` | 文件不存在 |
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| `DivideByZeroException` | 除数为零 |
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| `InvalidOperationException` | 操作无效状态 |
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## throw 抛出异常
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```csharp
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static void SetAge(int age)
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{
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if (age < 0 || age > 150)
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{
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throw new ArgumentException("年龄必须在 0-150 之间");
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}
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Console.WriteLine($"年龄设置为: {age}");
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}
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```
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```csharp
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try
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{
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SetAge(-5);
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}
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catch (ArgumentException ex)
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{
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Console.WriteLine($"参数错误: {ex.Message}");
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}
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```
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## 自定义异常
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```csharp
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class MicrophoneException : Exception
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{
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public MicrophoneException(string message) : base(message) { }
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public MicrophoneException(string message, Exception inner) : base(message, inner) { }
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}
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```
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## finally 的作用
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```csharp
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FileStream file = null;
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try
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{
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file = new FileStream("test.txt", FileMode.Open);
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// 读取文件...
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}
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catch (FileNotFoundException ex)
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{
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Console.WriteLine("文件不存在");
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}
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finally
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{
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// 确保文件被关闭
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file?.Close();
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}
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```
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## using 语句（更简洁）
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```csharp
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// using 自动释放资源（相当于 try-finally）
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using (FileStream file = new FileStream("test.txt", FileMode.Open))
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{
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// 使用 file
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} // 作用域结束后自动 Close()
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```
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## 实际项目应用
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```csharp
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try
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{
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// 尝试连接麦克风
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microphone.Connect();
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}
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catch (DeviceNotFoundException ex)
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{
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Console.WriteLine("麦克风未找到，请检查连接");
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ShowReconnectDialog();
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}
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catch (UnauthorizedAccessException ex)
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{
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Console.WriteLine("没有权限访问麦克风");
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RequestPermission();
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}
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catch (Exception ex)
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{
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Console.WriteLine($"未知错误: {ex.Message}");
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LogError(ex);
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}
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```
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## 不要过度捕获异常
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```csharp
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// ✗ 不好：捕获所有异常但不处理
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try { DoSomething(); }
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catch { }
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// ✓ 好：只捕获能处理的异常
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try { Connect(); }
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catch (DeviceNotFoundException ex) { ShowError(); }
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```
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