Question

更新改为我自己的接力命令有帮助。虽然生根Funcs没有

大家好我正在制作一个小型的MVVM应用程序。这应该是一个完整的课程 Func<string>并显示一个按钮列表，每个按钮执行一个包含Func<string>的命令，并在另一个列表中显示它们的返回值。

该程序首先工作正常但按下一个按钮后，它只是停止执行命令。用户界面仍然具有响应性。好像绑定破了。

有太多的课程，所以我将整个项目附加在以下链接

http://www.megafileupload.com/en/file/403770/GenericTester-zip.html

相关代码：

namespace AdapterTester.ViewModel
{
  public class MainViewModel : ViewModelBase
  {
    public ObservableCollection<ViewableRelayCommand> CommandsList { get; set; }
    public ObservableCollection<string> Log { get; set; }

    /// <summary>
    /// Initializes a new instance of the MainViewModel class.
    /// </summary>
    public MainViewModel()
    {
      CommandsList = new ObservableCollection<ViewableRelayCommand>();
      Log = new ObservableCollection<string>();
      MapCommands();
    }

    /// <summary>
    /// adds a ViewableRelayCommand to the CommandsList
    /// </summary>
    public void Add(Func<string> iCommand, string CommandName, Func<bool> CanExecute = null)
    {
      CommandsList.Add(new ViewableRelayCommand()
      {
        Command = new RelayCommand(() => { Log.Insert(0, "-------------\n" + CommandName  + "\n"  + (iCommand.Invoke())); }),
        CommandName = CommandName
      });
    }

    /// <summary>
    /// For Each Func<string> in TestFunctions create a ViewableRelayCommand
    /// </summary>
    private void MapCommands()
    {
      var target = new TestFunctions();
      var methods = target.GetType().GetMethods().Where(m => m.DeclaringType == typeof(TestFunctions));
      foreach (var method in methods)
      {
        if( (method.ReturnType == typeof(string)) && (method.GetParameters().Length ==0))
        {
          Func<string> func = (Func<string>)Delegate.CreateDelegate(typeof(Func<string>), target, method);
          Add(func, method.Name);
        }
      }
    }
  }

  public class ViewableRelayCommand : ViewModelBase
  {
    public RelayCommand Command { get; set; }

    /// <summary>
    /// The <see cref="CommandName" /> property's name.
    /// </summary>
    public const string CommandNamePropertyName = "CommandName";

    private string _CommandName = "Hello";

    /// <summary>
    /// Sets and gets the CommandName property.
    /// Changes to that property's value raise the PropertyChanged event. 
    /// </summary>
    public string CommandName
    {
      get
      {
        return _CommandName;
      }

      set
      {
        if (_CommandName == value)
        {
          return;
        }

        RaisePropertyChanging(CommandNamePropertyName);
        _CommandName = value;
        RaisePropertyChanged(CommandNamePropertyName);
      }
    }
  }
}

XAML：

<Window x:Class="AdapterTester.MainWindow"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
      xmlns:ignore="http://www.ignore.com"
      mc:Ignorable="d ignore"
      Width="500"
      Height="300"
      Title="MVVM Light Application"
      DataContext="{Binding Main, Source={StaticResource Locator}}">

  <Window.Resources>
    <ResourceDictionary>
      <ResourceDictionary.MergedDictionaries>
        <ResourceDictionary Source="Skins/MainSkin.xaml" />
      </ResourceDictionary.MergedDictionaries>
      <DataTemplate x:Key="myButtonTemplate">
        <Button Content="{Binding Path=CommandName}" Command="{Binding Path=Command}" Margin="3"></Button>
      </DataTemplate>
    </ResourceDictionary>
  </Window.Resources>

  <Grid>
    <Grid.ColumnDefinitions>
      <ColumnDefinition Width="*" />
      <ColumnDefinition Width="*" />
    </Grid.ColumnDefinitions>
    <ListBox Name="CommandsListBox" Grid.Column="0" 
             ItemsSource="{Binding CommandsList}"
             ItemTemplate="{StaticResource myButtonTemplate}">
    </ListBox>
     <ListBox Name="LogListBox" Grid.Column="1" 
                ItemsSource="{Binding Log}"
    </ListBox>
  </Grid>
</Window>

更新

答案是改变：

 Command = new RelayCommand(() => { Log.Insert(0, "-------------\n" + CommandName  + "\n"  + (iCommand.Invoke())); }),

这样的事情：

List<Action> actions = new List<Action>();
public void Add(Func<string> iCommand, string CommandName, Func<bool> CanExecute = null)
{
    Action act = () => { Log.Insert(0, "-------------\n" + CommandName + "\n" + (iCommand.Invoke())); };
    actions.Add(act);
    CommandsList.Add(new ViewableRelayCommand()
    {
        Command = new RelayCommand(act)
        ,
        CommandName = CommandName
    });
}

因为添加到中继命令的操作没有生根

Answer 1

是否使用MVVMLight的RelayCommand？

如果是这样，您可能会遇到GC问题。 RelayCommand在内部对其回调使用WeakReference。

如果您传入的是一个未在其他地方生根的匿名函数，那么当GC运行时它可能会被清除。

大多数情况下，这不是问题，因为func是对VM的回调，VM本身植根于DataContext，ViewModelLocator或其他地方。如果您正在创建未经过根植的Func，则可能是一个问题。

根据这些Func的一种方法是在ViewModel中有一个List<Func<string>>，并在创建RelayCommands的同时将它们添加到列表中。

Answer 2

Command = new RelayCommand(() => { Log.Insert(0, "-------------\n" + CommandName  + "\n"  + (Command.Invoke())); })

更改为：

Command = new RelayCommand(() => { Log.Insert(0, "-------------\n"); })

它可以工作，但我不知道为什么不能在Lambda表达式中使用参数（Command和CommandName）？

Answer 3

我是否正确地从命令中调用命令？

 Command = new RelayCommand(() => { Log.Insert(0, "-------------\n" + CommandName  + "\n"  + (Command.Invoke())); })

这不是递归吗？

您可以尝试从表达式中删除调用吗？你为什么要从里面调用它？

命令停止执行

3 个答案: