创建抽象 ViewModels wpf

Question

我正在尝试创建一个抽象 ViewModel class，以及几个将继承抽象 ViewModel 并实现它的 ViewModel classes。

到目前为止，我使用的是 RelayCommand，但无法编译。

这样的事情能做吗？

我正在添加我的代码：

中继命令class:

public class RelayCommand : ICommand
{
    private readonly Action<object> m_executeAction;
    private readonly Predicate<object> m_canExecute;

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

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

        m_executeAction = executeAction;
        m_canExecute = canExecute;
    }

    public bool CanExecute(object canExecuteParameter)
    {
        return (m_canExecute == null || m_canExecute(canExecuteParameter));
    }

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

    public void Execute(object canExecuteParameter)
    {
        m_executeAction(canExecuteParameter);
    }
}

ViewModelsBase class:

public abstract class ViewModelBase : INotifyPropertyChanged, IDisposable
{
    public event PropertyChangedEventHandler PropertyChanged;

    public void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged == null) return;
        PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }

    protected virtual void OnDispose() {}

    public void Dispose()
    {
        OnDispose();
    }
}

MainViewModel class:

public class MainWindowViewModel : ViewModelBase
{
    private IViewModel m_testViewModel;
    private bool m_isFirstPlugin = true;

    public MainWindowViewModel()
    {
        TestViewModel = new FirstViewModel();
    }

    public IViewModel TestViewModel
    {
        get { return m_testViewModel; }
        set
        {
            m_testViewModel = value;
            OnPropertyChanged("NewViewModel");
        }
    }

    private ICommand m_changeCommand;

    public ICommand ChangeCommand
    {
        get { return m_changeCommand ?? (m_changeCommand = new RelayCommand(Change)); }
        set { m_changeCommand = value; }
    }

    private void Change(object parameter)
    {
        TestViewModel.Dispose();
        TestViewModel = null;

        if (m_isFirstPlugin)
            TestViewModel = new SecondViewModel();
        else
            TestViewModel = new FirstViewModel();

        m_isFirstPlugin = !m_isFirstPlugin;
    }
}

IViewModel class:

public class IViewModel : ViewModelBase
{
    private ICommand m_testCommand;

    public ICommand TestCommand
    {
        get { return m_testCommand ?? (m_testCommand = new RelayCommand(Test)); }
        set { m_testCommand = value; }
    }

    protected virtual void Test(object parameter) { }
}

FirstViewModel class:

public class FirstViewModel : IViewModel
{
    protected override void Test(object parameter)
    {
        MessageBox.Show("On First Plugin.");
    }
}

SecondViewModel class:

public class SecondViewModel : IViewModel
{
    protected override void Test(object parameter)
    {
        MessageBox.Show("On Second Plugin.");
    }
}

Xaml:

<Window x:Class="MvvmInheritence.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="Testing" Height="100" Width="180"
    xmlns:Local="clr-namespace:MvvmInheritence" WindowStartupLocation="CenterScreen" Background="Transparent">
    <Window.DataContext>
        <Local:MainWindowViewModel />
    </Window.DataContext>
    <Grid x:Name="MainGrid">
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition />
        </Grid.RowDefinitions>
        <Button x:Name="TestButton" Content="Test!" Foreground="DarkRed" Background="LightBlue"  Height="25" Width="100" Command="{Binding TestCommand, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" DataContext="{Binding TestViewModel, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Grid.Row="0"/>
        <Button x:Name="ChangeButton" Content="Change Plugin" Foreground="DarkRed" Background="LightBlue"  Height="25" Width="100" Command="{Binding ChangeCommand, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Grid.Row="1"/>
    </Grid>
</Window>

此代码确实可以编译（我进行了更改以使其工作）但出于某种原因，我总是得到 "On First Plugin" 即使 Change 函数被调用，并且 ViewModel 已正确更改。

我错过了什么？

Answer 1

自定义 MVVM 从创建实现 INotifyPropertyChanged 接口的抽象 ViewModelBase class 开始。

但是，根据您的 RelayCommand 评论，我假设您使用的是 MVVM Light 框架？然后而不是实施 INotifyPropertyChanged 你的抽象 ViewModel 应该继承自 MVVM Lights ViewModelBase class.

RelayCommands 将是您的 ViewModelBase 的属性，而不是您继承自的基础 class。

Answer 2

好的，我找到了故障。

在 MainViewModel class 中，TestViewModel 属性应更改为：

public IViewModel TestViewModel
{
    get { return m_testViewModel; }
    set
    {
        m_testViewModel = value;
        OnPropertyChanged("NewViewModel");
    }
}

收件人：

public IViewModel TestViewModel
{
    get { return m_testViewModel; }
    set
    {
        m_testViewModel = value;
        OnPropertyChanged("TestViewModel");
    }
}

创建抽象 ViewModels wpf

Creating abstract ViewModels wpf

c#

wpf

inheritance

viewmodel

relaycommand