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UWP-命令参数为空

• 问答

我正在使用RelayCommand，它是由microsoft在其ICommand example中实现的。这是我的代码简介。

XAML： 

<TextBox x:Name="YoutubeUrlText"
         PlaceholderText="Insert link from youtube here... "
         FontSize="20" FontStyle="Italic" Width="450" />
<Button x:Name="ConvertButton" FontFamily="Segoe MDL2 Assets" FontSize="20" Content="&#xE751;"
        Grid.Column="1" Height="40"
        HorizontalAlignment="Left" VerticalAlignment="Center" 
        Foreground="White" BorderBrush="#FF797979" Background="#FF0096FF" 
        Command="{x:Bind urlSearchViewModel._GetVideo(YoutubeUrlText.Text)}"/>

XAML背后的代码： 

    public sealed partial class UrlSearchPage : Page
    {
        public UrlSearchViewModel urlSearchViewModel;
        public UrlSearchPage()
        {
            this.InitializeComponent();
            urlSearchViewModel = new UrlSearchViewModel();
        }
    }

ViewModel代码： 

        public RelayCommand _GetVideo(string url)
        {
            return new RelayCommand(() => this.getVideo(url));
        }

        private void getVideo(string url)
        {
            try
            {
                FileInfo mp4 = youtubeConverter.DownloadVideoAsync(url,YoutubeConverter.TemporaryFolder).Getawaiter().GetResult();
            }
            catch (Exception ex)
            {

                Debug.WriteLine(ex.Message);
            }
        }

例如，只需忽略愚蠢的异步部分。问题是url始终是一个空字符串，因此每次按下Exception时都会收到Button。

iCMS 回答：UWP-命令参数为空

UWP-命令参数为空

恐怕您不能将命令与包含参数且返回类型为RelayCommand的方法绑定。请参考以下代码并编辑命令，并使用CommandParameter属性传递参数。

public class UrlSearchViewModel
{

    public ICommand GetVideo
    {
        get
        {
            return new CommadEventHandler<string>((s) => this.getVideo(s));
        }

    }

    private void getVideo(string url)
    {
        try
        {

        }
        catch (Exception ex)
        {
            Debug.WriteLine(ex.Message);
        }
    }
}


public class CommadEventHandler<T> : ICommand
{
    public event EventHandler CanExecuteChanged;

    public Action<T> action;
    public bool CanExecute(object parameter)
    {
        return true;
    }

    public void Execute(object parameter)
    {
        this.action((T)parameter);
    }
    public CommadEventHandler(Action<T> action)
    {
        this.action = action;

    }
}

Xaml 

<Grid Background="GreenYellow">
    <TextBox
        x:Name="YoutubeUrlText"
        Width="450"
        VerticalAlignment="Top"
        FontSize="20"
        FontStyle="Italic"
        PlaceholderText="Insert link from youtube here... "
        />
    <Button
        x:Name="ConvertButton"
        Grid.Column="1"
        Height="40"
        HorizontalAlignment="Left"
        VerticalAlignment="Center"
        Background="#FF0096FF"
        BorderBrush="#FF797979"       
        Command="{x:Bind urlSearchViewModel.GetVideo}"
        CommandParameter="{Binding ElementName=YoutubeUrlText,Path=Text}"
        Content="&#xE751;"
        FontFamily="Segoe MDL2 Assets"
        FontSize="20"
        Foreground="White"
        />
</Grid>
c#icommandmvvmuwpxaml
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