c# – 命令停止执行

2023年12月16日 140次阅读

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MVVM应用程序.这应该是一个完整的课程
FUNC<串GT;并显示每个执行包含Func< string>的命令的按钮列表.并在另一个列表中显示其返回值.

该程序首先工作正常,但在按下一个按钮后,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.

有太多的类,所以我将整个项目附加在以下链接中

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relay命令的操作没有root

最佳答案 它是否使用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.如果你创建的Func不是root,那可能是个问题.

根这些Func的一种方法是使用List< Func< string>>在ViewModel中,并在创建RelayCommands的同时将它们添加到列表中.

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