Question

我正在开发一个Windows Phone 8，我有一个选择列表框和这个方法：

private void locationsList_SelectionChanged(object sender, System.Windows.Controls.SelectionChangedEventArgs e)
{
    ARLocation item = (ARLocation)locationsList.SelectedItem;

    NavigationService.Navigate(new Uri("/Views/MapPage.xaml", UriKind.Relative));
    locationsList.SelectedItem = null;
}

当我执行locationsList.SelectedItem = null;时，会再次触发SelectionChanged事件。

当我清除SelectedItem时，如何避免触发事件？

Answer 1

除非您不想取消订阅该活动，否则您无法避免 - 您正在更改所选项目，因此它会触发该活动。

您可以尝试做这样的事情 - 取消订阅然后订阅活动：

locationsList.SelectioChanged -= locationsList_SelectionChanged;
locationsList.SelectedItem = null;
locationsList.SelectioChanged += locationsList_SelectionChanged;

但在这种情况下执行检查可能更容易：

private void locationsList_SelectionChanged(object sender, System.Windows.Controls.SelectionChangedEventArgs e)
{
  if ((sender as ListBox).SelectedItem != null)
  {
    ARLocation item = (ARLocation)locationsList.SelectedItem;

    NavigationService.Navigate(new Uri("/Views/MapPage.xaml", UriKind.Relative));
    locationsList.SelectedItem = null;
  }
}

或者您可以提供一个布尔值来通知事件应该跳过它：

private bool SkipEvent = false;

private void locationsList_SelectionChanged(object sender, System.Windows.Controls.SelectionChangedEventArgs e)
{
  if (SkipEvent) return;
  ARLocation item = (ARLocation)locationsList.SelectedItem;

  NavigationService.Navigate(new Uri("/Views/MapPage.xaml", UriKind.Relative));

  // Skip block:
  try
  {
    SkipEvent = true;
    locationsList.SelectedItem = null;
  }
  finally { SkipEvent = false; }
}

当我将SelectedItem设置为null时，避免再次触发_SelectionChanged

1 个答案: