问题描述
有没有办法打破foreach扩展方法? break关键字不能将扩展方法识别为有效的作用域。 //不能编译ForEach(i => {System.Windows.MessageBox.Show(i.ToString()); if(i> 2)break;}) ;
$ b 编辑:从问题中删除linq p>
请注意代码只是一个示例,显示break在扩展方法中不起作用...我真正想要的是用户能够中止处理列表.. UI线程有一个中止变量和for循环只是当用户点击取消按钮时打破。现在,我有一个正常的循环,但我想看看是否有可能做的扩展方法。
解决方案把这个称为 List< T>
Foreach与LINQ之间可能更准确。
尽管如此,没有办法打破这个循环。主要是因为它实际上并不是一个循环。这是一个方法,它需要在循环内部调用一个委托。
创建一个具有中断能力的ForEach是非常直接的,但是
pre $ public delegate void ForEachAction< T>(T value,ref bool doBreak);
public static void ForEach< T>(this IEnumerable< T> enumerable,ForEachAction< T> action){
var doBreak = false;
foreach(var cur in enumerable){
action(cur,ref doBreak);
if(doBreak){
break;
你可以重写你的代码如下所示:
Enumerable.Range(0,10)
.ForEach((int i,ref bool doBreak) => {
System.Windows.MessageBox.Show(i.ToString());
if(i> 2){doBreak = true;}
});
is there a way to break out of the foreach extension method? The "break" keyword doesn't recognize the extension method as a valid scope to break from.
//Doesn't compile
Enumerable.Range(0, 10).ToList().ForEach(i => { System.Windows.MessageBox.Show(i.ToString()); if (i > 2)break; });
Edit: removed "linq" from question
note the code is just an example to show break not working in the extension method... really what I want is for the user to be able to abort processing a list.. the UI thread has an abort variable and the for loop just breaks when the user hits a cancel button. Right now, I have a normal for loop, but I wanted to see if it was possible to do with the extension method.
解决方案 It's probably more accurate to call this a List<T>
Foreach vs. a LINQ one.
In either case though no there is no way to break out of this loop. Primarily because it's not actually a loop per say. It's a method which takes a delegate that is called inside a loop.
Creating a ForEach with break capability is fairly straight forward though
public delegate void ForEachAction<T>(T value, ref bool doBreak);
public static void ForEach<T>(this IEnumerable<T> enumerable, ForEachAction<T> action) {
var doBreak = false;
foreach (var cur in enumerable) {
action(cur, ref doBreak);
if (doBreak) {
break;
}
}
}
You could then rewrite your code as the following
Enumerable.Range(0,10)
.ForEach((int i,ref bool doBreak) => {
System.Windows.MessageBox.Show(i.ToString());
if ( i > 2) {doBreak = true;}
});
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