如何将命令和上下文从 UserControl 绑定到 MainView UWP MVVM

Question

有标签所在的窗体，以及包裹在按钮中的用户控件。我需要通过单击用户控件中的按钮来更改 TextBlock 中的文本。我没有使用任何 MVVM 框架。主要 XAML:

    <Page.DataContext>
    <local:MainViewModel />
</Page.DataContext>

<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="553*" />
        <ColumnDefinition Width="197*" />
    </Grid.ColumnDefinitions>
    <local:ControlView Grid.Column="1" HorizontalAlignment="Stretch"
                       VerticalAlignment="Stretch" />
    <TextBlock Grid.Column="0" Foreground="Black" FontSize="50" VerticalAlignment="Stretch"
               HorizontalAlignment="Stretch" Text="{Binding UserText, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
    
</Grid>

用户控制Xaml:

<Grid>
    <Button Width="300" Height="100" FontSize="50" Command="{Binding}"
            VerticalAlignment="Center" HorizontalAlignment="Center" Content="Print chart" />
</Grid>

主虚拟机：

 public class MainViewModel : INotifyPropertyChanged
{
    public MainViewModel()
    {
        
        SetText = new RelayCommand(SetUserText);
    }

    public ICommand SetText { get; set; }

    public string UserText { get; set; }

    
    public event PropertyChangedEventHandler PropertyChanged;

    private void SetUserText()
    {
        UserText = "Hello World!";
        RaisePropertyChanged(nameof(UserText ));
    }

    
    protected void RaisePropertyChanged(string property)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(property));
    }
}

然后我创建一个空的用户控件 VN:

public class ControlViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    protected void RaisePropertyChanged(string property)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(property));
    }

    // And what should I do here?
}

那么如何正确实现从用户控件到主视图的命令，f.e SetText 属性?

Answer 1

您的主要问题是 ControlViewModel 的使用。 UserControls 例如 ControlView 一般而言不应将自己的 DataContext 设置为某些专门的视图模型，而是从其父元素继承 DataContext。

假设您让控件继承 DataContext，您可以向其添加依赖项属性并将命令绑定到此：

<local:ControlView YourCommand="{Binding SetText}" />

ControlView.xaml:

<UserControl ... Name="uc">
    <Button Command="{Binding YourCommand, ElementName=uc}" />

如何将命令和上下文从 UserControl 绑定到 MainView UWP MVVM

How to bind command and contexrt from UserControl to MainView UWP MVVM

c#

datacontext

mvvm

uwp