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我正在编写一个 WPF 应用程序并尝试自学 MVVM 模式。我正在使用 Samuel Jack 网站上的说明：http: //blog.functionalfun.net/2008/09/hooking-up-commands-to-events-in-wpf.html

我已将命令绑定到按钮并将所有内容连接起来。命令类是 ViewModel 类的内部类，它实现了 ICommand。复杂的部分是当从我的按钮运行的命令需要访问我的视图上的数据时。由于 C# 内部类无法访问外部类的成员，因此我发现自己必须在 ViewModel 类中声明公共静态变量才能将数据传递给内部类。这似乎是一个 hackish 和不雅的解决方案。有没有人有更好的方法来做到这一点？

我的视图模型代码：

public class ApplicationViewModel
{
    public ObservableCollection<App> AppCollection { get; set; }
    static string searchString;
    static string emailString;
    public App SelectedApp { get; set; }
    public string AppToSearch
    {
        get
        {
            return searchString;
        }
        set
        {
            searchString = value;
        }
    }
    public string AppToRequest
    {
        get
        {
            get emailString;
        }
        set
        {
            // set static email String here
        }
    }
    private SearchButtonCommand searchButtonCmd;
    private ClearButtonCommand clearButtonCmd;
    private EmailButtonCommand emailButtonCmd;

    public ApplicationViewModel()
    {
        this.AppCollection = ApplicationsModel.Current;
    }

    public ICommand SearchButtonPressed
    {
        get
        {
            if (this.searchButtonCmd == null)
            {
                this.searchButtonCmd = new SearchButtonCommand();
            }
            return this.searchButtonCmd;
        }
    }

    public ICommand ClearButtonPressed
    {
        get
        {
            if (this.clearButtonCmd == null)
            {
                this.clearButtonCmd = new ClearButtonCommand();
            }
            return this.clearButtonCmd;
        }
    }

    public ICommand EmailButtonPressed
    {
        get
        {
            if (this.emailButtonCmd == null)
            {
                this.emailButtonCmd = new EmailButtonCommand();
            }
            return this.emailButtonCmd;
        }
    }

    private class SearchButtonCommand : ICommand
    {
        public event EventHandler CanExecuteChanged;

        public void Execute(object parameter)
        {
            string searchkey = ApplicationViewModel.searchString;
            ApplicationsModel.Current.Search(searchkey);
        }

        public bool CanExecute(object parameter)
        {
            return true;
        }
    }

    private class ClearButtonCommand : ICommand
    {
        public event EventHandler CanExecuteChanged;

        public void Execute(object parameter)
        {
            ApplicationsModel.Current.ClearSearch();
        }

        public bool CanExecute(object parameter)
        {
            return true;
        }
    }

    private class EmailButtonCommand : ICommand
    {
        public event EventHandler CanExecuteChanged;

        public void Execute(object parameter)
        {
            string targetEmail = ApplicationViewModel.emailString;
        }

        public bool CanExecute(object parameter)
        {
            return true;
        }
    }
}

我的 XAML：

<Window.DataContext>
    <vm:ApplicationViewModel />
</Window.DataContext>

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto" />
        <RowDefinition Height="Auto" />
        <RowDefinition Height="*" />
        <RowDefinition Height="Auto" />
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="*" />
    </Grid.ColumnDefinitions>
    <Image Grid.Row="0" Height="84" HorizontalAlignment="Left" Margin="0,5,5,5" Name="imgLogo" Stretch="Fill" VerticalAlignment="Top" Width="600" Source="C:\Images\bannerlong.png" />
    <Grid Grid.Row="1" HorizontalAlignment="Center" Margin="0,5,5,5" VerticalAlignment="Center">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto" />
            <ColumnDefinition Width="Auto" />
            <ColumnDefinition Width="Auto" />
            <ColumnDefinition Width="Auto" />
        </Grid.ColumnDefinitions>
        <Label Grid.Row="0" Grid.Column="0" Content="Search for Application">
            <Label.Foreground>
                <SolidColorBrush Color="LightCyan" />
            </Label.Foreground>
        </Label>
        <TextBox Grid.Row="0" Grid.Column="1" Margin="3" Width="500" Text="{Binding AppToSearch}" />
        <Button Grid.Row="0" Grid.Column="2" HorizontalAlignment="Right" Width="100" Height="20" Margin="3" Background="LightCyan" Content="Search" vm:ButtonBehaviour.SearchCommand="{Binding SearchButtonPressed}" />
        <Button Grid.Row="0" Grid.Column="3" HorizontalAlignment="Right" Width="100" Height="20" Margin="3" Background="LightCyan" Content="Clear Search" vm:ButtonBehaviour.ClearCommand="{Binding ClearButtonPressed}"/>
    </Grid>
    <ListView Grid.Row="2" BorderBrush="Black" HorizontalAlignment="Stretch" ItemsSource="{Binding Path=AppCollection}" SelectedItem="{Binding SelectedApp}">
        <ListView.View>
            <GridView>
                <GridViewColumn Header="Application Name" Width="100" DisplayMemberBinding="{Binding Name}"/>
                <GridViewColumn Header="Application Description" Width="800" DisplayMemberBinding="{Binding Description}"/>
                <GridViewColumn Header="Application Owner" Width="100" DisplayMemberBinding="{Binding Owner}"/>
            </GridView>
        </ListView.View>
    </ListView>
    <Button Grid.Row="3" HorizontalAlignment="Center" Width="200" Height="30" Margin="3" Background="LightCyan" Content="Request Application" vm:ButtonBehaviour.EmailCommand="{Binding EmailButtonPressed}" />
</Grid>

非常感谢！

4

2 回答 2

1

你可以在你的视图模型中有一个委托或事件，你的命令类用来获取数据

.. 或者您可以通过命令参数将数据从视图传递到命令。

Button Command="{Binding SaveCommand}" 
        CommandParameter="{Binding SelectedItem, Element=listBox}" />
于 2013-02-14T20:18:37.930 回答
1

您可以定义一个RelayCommand允许您调用委托的类。使用这种方法，您不需要为每个命令声明一个类。

public class RelayCommand : ICommand
{
    #region Miembros

    readonly Action<object> _execute;
    readonly Predicate<object> _canExecute;

    #endregion

    #region Constructor

    public RelayCommand(Action<object> execute)
        : this(execute, null)
    {
    }

    public RelayCommand(Action<object> execute, Predicate<object> canExecute)
    {
        if (execute == null)
        {
            throw new ArgumentNullException("execute");
        }

        _execute = execute;
        _canExecute = canExecute;
    }

    #endregion

    #region Miembros de ICommand

    public bool CanExecute(object parameter)
    {
        return _canExecute == null || _canExecute(parameter);
    }

    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }

    public void Execute(object parameter)
    {
        _execute(parameter);
    }

    #endregion
}

然后您的 ViewModel 类将类似于：

public class ApplicationViewModel
{
    public ObservableCollection<App> AppCollection { get; set; }
    private string searchString;
    private string emailString;
    public App SelectedApp { get; set; }
    public string AppToSearch
    {
        get
        {
            return searchString;
        }
        set
        {
            searchString = value;
        }
    }
    public string AppToRequest
    {
        get
        {
            return emailString;
        }
        set { emailString = value; }
    }

    private ICommand searchButtonCmd;
    private ICommand clearButtonCmd;
    private ICommand emailButtonCmd;

    public ApplicationViewModel()
    {
        this.AppCollection = ApplicationsModel.Current;
    }

    public ICommand SearchButtonPressed
    {
        get
        {
            if (this.searchButtonCmd == null)
            {
                this.searchButtonCmd = new RelayCommand(SearchButtonPressedExecute, c=>CanSearch);
            }
            return this.searchButtonCmd;
        }
    }

    private void SearchButtonPressedExecute(object parameter)
    {
        ApplicationsModel.Current.Search(searchString);
    }

    public bool CanSearch
    {
        get { return true; }
    }

    // TODO: You can figure out the rest of the code
}

不要忘记更新 Button 的 XAML，例如：

<Button Grid.Row="0" Grid.Column="2" HorizontalAlignment="Right" Width="100" Height="20" Margin="3" Background="LightCyan" Content="Search" Command="{Binding SearchButtonPressed}" />

其他按钮也是如此。

希望这可以帮助！

于 2013-02-14T20:33:26.143 回答