Windows phone 7 再次避免触发\u SelectionChanged当我将SelectedItem设置为null时

我正在开发Windows Phone 8，我有一个单一的选择列表框和此方法：

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

再次触发

SelectionChanged

事件

---

如何避免在清除SelectedItem时触发该事件？

除非您不想取消订阅该事件，否则无法避免它-您正在更改所选项目，因此它将触发该事件

您可以尝试这样做-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，进行检查可能更容易：

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; }
}

---

除非您不想取消订阅该活动，否则无法避免-您正在更改所选项目，因此它将触发该活动

您可以尝试这样做-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，进行检查可能更容易：

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; }
}

---

除非您不想取消订阅该活动，否则无法避免-您正在更改所选项目，因此它将触发该活动

您可以尝试这样做-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，进行检查可能更容易：

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; }
}

---

除非您不想取消订阅该活动，否则无法避免-您正在更改所选项目，因此它将触发该活动

您可以尝试这样做-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，进行检查可能更容易：

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; }
}