观察-观察性宣言

Question

不知何故，这在运行时不起作用(但它正在编译)：

    public static readonly DependencyProperty SelectedVideoFileNamesProperty =
    DependencyProperty.Register("SelectedVideoFileNames", typeof(ObservableCollection<ObservableCollection<string>>), typeof(CMiX_UI), 
        new PropertyMetadata(new[]{new ObservableCollection<string>(),
                                   new ObservableCollection<string>(),
                                   new ObservableCollection<string>(),
                                   new ObservableCollection<string>(),
                                   new ObservableCollection<string>(),
                                   new ObservableCollection<string>()}));
    [Bindable(true)]
    public ObservableCollection<ObservableCollection<string>> SelectedVideoFileNames
    {
        get { return (ObservableCollection<ObservableCollection<string>>)this.GetValue(SelectedVideoFileNamesProperty); }
        set { this.SetValue(SelectedVideoFileNamesProperty, value); }
    }

为什么？谢谢

Answer 1

它不应该运行，因为您将字符串ObservableCollection的ObservableCollection<string>[]数组指定为ObservableCollection<ObservableCollection<string>>的默认值。如果您像这样编写代码：

        ObservableCollection<ObservableCollection<string>> o = new[]{new ObservableCollection<string>(),
                               new ObservableCollection<string>(),
                               new ObservableCollection<string>(),
                               new ObservableCollection<string>(),
                               new ObservableCollection<string>(),
                               new ObservableCollection<string>()};

它将给您一个设计时错误，即：

不能隐式地将类型'System.Collections.ObjectModel.ObservableCollection[]‘转换为'System.Collections.ObjectModel.ObservableCollection>’

相反，你可以：

        ObservableCollection<ObservableCollection<string>> o = new ObservableCollection<ObservableCollection<string>> {new ObservableCollection<string>(),
                               new ObservableCollection<string>(),
                               new ObservableCollection<string>(),
                               new ObservableCollection<string>(),
                               new ObservableCollection<string>(),
                               new ObservableCollection<string>()};

Answer 2

类型定义为

ObservableCollection<ObservableCollection<string>>

但是，您将默认设置为：

new[]{new ObservableCollection<string>(),
                               new ObservableCollection<string>(),
                               new ObservableCollection<string>(),
                               new ObservableCollection<string>(),
                               new ObservableCollection<string>(),
                               new ObservableCollection<string>()}))

这是一组可观察的集合。你需要：

new ObservableCollection<ObservableCollection<String()>> {new ObservableCollection<string>(),
                               new ObservableCollection<string>(),
                               new ObservableCollection<string>(),
                               new ObservableCollection<string>(),
                               new ObservableCollection<string>(),
                               new ObservableCollection<string>()}))