c# - for循环中事件处理程序的匿名方法

Question

这可以在 for 循环中完成吗？

        TickEventArgs targs1 = new TickEventArgs(lbl1_up_time, _elapsedTime_up1);
        timer_up1.Tick += (sender, e) => Tick(targs1);

        TickEventArgs targs2 = new TickEventArgs(lbl2_up_time, _elapsedTime_up2);
        timer_up2.Tick += (sender, e) => Tick(targs2);

        TickEventArgs targs3 = new TickEventArgs(lbl3_up_time, _elapsedTime_up3);
        timer_up3.Tick += (sender, e) => Tick(targs3);

        TickEventArgs targs4 = new TickEventArgs(lbl4_up_time, _elapsedTime_up4);
        timer_up4.Tick += (sender, e) => Tick(targs4);

        TickEventArgs targs5 = new TickEventArgs(lbl5_up_time, _elapsedTime_up5);
        timer_up5.Tick += (sender, e) => Tick(targs5);

这行不通，因为我超出了范围 (5)

        targs[0] = new TickEventArgs(lbl1_up_time, _elapsedTime_up1);
        targs[1] = new TickEventArgs(lbl2_up_time, _elapsedTime_up2);
        targs[2] = new TickEventArgs(lbl3_up_time, _elapsedTime_up3);
        targs[3] = new TickEventArgs(lbl4_up_time, _elapsedTime_up4);
        targs[4] = new TickEventArgs(lbl5_up_time, _elapsedTime_up5);

        timers[0] = timer_up1;
        timers[1] = timer_up2;
        timers[2] = timer_up3;
        timers[3] = timer_up4;
        timers[4] = timer_up5;

        int i = 0;

        for (i = 0; i <= 4; i++)
        {
            timers[i].Tick += (sender, e) => Tick(targs[i]);
        } 

Answer 1

这来自 lambda 表达式； 我 is shared between all of them .当函数被执行时，它们实际上被调用为 timers[i].Tick += (sender, e) => Tick(targs[5])。

为避免这种情况，请创建一个局部范围的变量 (int locali = i) 并在您的行中使用它。这将确保每个 lambda 表达式实际获得您期望的值。

for (i = 0; i <= 4; i++)
{
    int locali = i;
    timers[locali].Tick += (sender, e) => Tick(targs[locali]);
} 

i 在退出之前从循环的最后一次迭代变为 5。当然，您没有 targs[5] 元素，因此它会抛出 IndexOutOfRangeException。

从技术上讲，您不需要对 timers[i].Tick 部分使用 locali，因为它会立即求值，但我个人觉得混合使用两个。

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关于概念的一些额外阅读:

The foreach identifier and closures

Closing over the loop variable considered harmful