WPF MVVM Light - SelectedItem 的绑定(bind)没有改变

Question

这个领域有很多帖子，但没有一个对我有帮助......这是场景:我有两个“季节”下拉菜单来模拟一个范围。如果您在开始范围内选择一个季节，viewmodele 会自动将绑定(bind)到结束范围的属性设置为同一季节(因此它默认为一年而不是范围。这就是 XAML 的样子(删除了很​​多格式化属性以提高可读性):

<ComboBox ItemsSource="{Binding AvailableSeasons, Mode=OneWay}" 
          SelectedItem="{Binding SelectedBeginRangeSeason, Mode=TwoWay}" 
          ItemTemplate="{DynamicResource SeasonItemShortFormat}" />
<ComboBox ItemsSource="{Binding AvailableSeasons, Mode=OneWay}" 
          SelectedItem="{Binding SelectedEndRangeSeason, Mode=TwoWay}" 
          ItemTemplate="{DynamicResource SeasonItemShortFormat}" />

View 模型中的属性如下所示:

private Season _selectedBeginRangeSeason;
private const string SelectedBeginRangeSeasonPropertyName = "SelectedBeginRangeSeason";
public Season SelectedBeginRangeSeason {
  get { return _selectedBeginRangeSeason; }
  set {
    if (_selectedBeginRangeSeason != value) {
      var oldValue = _selectedBeginRangeSeason;
      _selectedBeginRangeSeason = value;

      RaisePropertyChanged<Season>(SelectedBeginRangeSeasonPropertyName, oldValue, value, true);
    }
  }
}

private Season _selectedEndRangeSeason;
private const string SelectedEndRangeSeasonPropertyName = "SelectedEndRangeSeason";
public Season SelectedEndRangeSeason {
  get { return _selectedEndRangeSeason; }
  set {
    if (_selectedEndRangeSeason != value) {
      Debug.WriteLine("Updating property SelectedEndRangeSeason...");

      var oldValue = _selectedEndRangeSeason;
      _selectedEndRangeSeason = value;

      Debug.WriteLine("Broadcasting PropertyChanged event for property SelectedEndRangeSeason...");
      RaisePropertyChanged<Season>(SelectedEndRangeSeasonPropertyName, oldValue, value, true);
    }
  }
}

private void UpdateSelectedSeasonSelectors() {
  // if the end range isn't selected...
  if (_selectedEndRangeSeason == null) {
    // automatically select the begin for the end range
    SelectedEndRangeSeason = _selectedBeginRangeSeason;
  }
}

我已经通过调试语句和单元测试验证了 end 属性正在更改，但是当我选择它时 UI 并没有改变......无法弄清楚发生了什么并查看了这么多不同方法...

Answer 1

你收到了SelectedSeason来自 AvailableSeasons收藏？如果没有，您是否实现了一些特别的措施来比较季节？

例如，假设您有

<ComboBox ItemsSource="{Binding AvailableSeasons}" 
          SelectedItem="{Binding SelectedSeason}" />

如果 SelectedSeason = new Season(); SelectedItem 绑定(bind)不起作用，因为 new Season();在 AvailableSeasons 中不存在.

您需要设置 SelectedSeason = AvailableSeasons[x]为 SelectedItem 工作，因为这使两个项目完全相同。或者您可以实现一些自定义方法来比较两个季节，看看它们是否相同。通常我只是覆盖 ToString()被比较的类的方法。