在foreach循环闭合内中断开关 [英] breaking out of a switch within a foreach loop closure

问题描述

我有以下代码

 void onSelectionChangedFiredSources( Event event, var detail,
                                SelectCheckboxMenuComponent target)
  {
    // getItemModels returns a list of objects
      getItemModels( target.selectedItems )
        ..forEach( (item)
          {          
             switch( item.label )
             {
               case 'Ear':
                 toggleDialog( 'paper-dialog-transition-center',
                                $['ear-side-dialog']);
                 break;

               case 'Eye':
                 toggleDialog( 'paper-dialog-transition-center',
                                $['eye-side-dialog']);
                 break;

               case 'Nostril':
                 toggleDialog( 'paper-dialog-transition-center',
                                $['nostril-side-dialog']);
                 break;

               case 'Thorax':
                 toggleDialog( 'paper-dialog-transition-center',
                                $['thorax-side-dialog']);
                 break;

               default:
                 srcDataMap.add( item.label, item.selected);
             }   
          });
  }

触发案例时，我想跳出foreach循环.

When a case is triggered, I would like to break out of the foreach loop.

请注意，每次选择更改时，所有选择均由target.selectedItems表达式返回.因此，如果首先选择"Ear"，则执行循环，然后选择"Eye"时，列表返回将同时包含"Ear"和"Eye".如何做到最好?谢谢

Note that each time the selection changes, all selections are return by the target.selectedItems expression. So if 'Ear' is the first selection, the loop is executed and when 'Eye' is then selected the list return will have both Ear and Eye. How is this best done? Thanks

推荐答案

您不能中断 forEach 调用.

您不能使用 break ，因为它不是循环.这是一个函数调用，而break仅在当前函数内部起作用.

You can't use break because it's not a loop. It's a function call, and break only works inside the current function.

您不能返回，因为那只会继续下一个元素.

You can't return, because that just continues with the next element.

您可以 扔结束 forEach ，但这并不漂亮.

You can throw to end the forEach, but that's hardly pretty.

相反，您可以做的是根本不使用 forEach ，而是使用 for-in 循环，然后使用以下方法 break 标记为中断:

What you can do instead is to not use forEach at all, and use a for-in loop instead, and then break out of that using a labeled break:

void onSelectionChangedFiredSources(Event event, var detail,
                                    SelectCheckboxMenuComponent target) {
  // getItemModels returns a list of objects
  var models = getItemModels(target.selectedItems);
  loop: for (var item in models) {
    switch (item.label) {
      case 'Ear':
      case 'Eye':
      case 'Nostril':
      case 'Thorax':
        toggleDialog('paper-dialog-transition-center',
                     $['${item.label.toLowerCase()}-side-dialog']);
        break loop;
      default:
        srcDataMap.add( item.label, item.selected);
    }   
  }
}

您需要使用带标签的 break ，因为没有标签只会破坏 switch 语句.

You need to use a labeled break because without a label it would only be breaking the switch statement.

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