c# - MVVM 在单击时更改网格的背景颜色

Question

我是 MVVM 模式的真正初学者。我试图在单击按钮时更改网格的背景。我有一个带有包含按钮的网格的 xaml，以及我想在单击按钮时更改网格背景的 ViewModel .cs。直到我点击时才成功显示一个 MessageBox ...

.xaml代码:

<Window x:Class="WpfSimple.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:WpfSimple"
    Title="MainWindow" Height="150" Width="370">
<Window.DataContext>
    <local:MainWindowViewModel/>
</Window.DataContext>
    <Grid>
    <Button Content="Click" 
            Height="23" 
            HorizontalAlignment="Left"
            Background="Gray"
            Margin="75.944,47.465,0,0" 
            Name="btnClick" 
            VerticalAlignment="Top" 
            Width="203"
            Command="{Binding ButtonCommand}"/>
        <!--What is necessary to add for changing grid color ? Commandparameter ?-->
</Grid>

MainWindowViewModel.cs代码:

namespace WpfSimple
{
    class MainWindowViewModel
    {
        private ICommand m_ButtonCommand;
        public ICommand ButtonCommand
        {
            get
            {
                return m_ButtonCommand;
            }
            set
            {
                m_ButtonCommand = value;
            }
        }

        public MainWindowViewModel()
        {
            ButtonCommand=new RelayCommand(new Action<object>(ChangeBgColor));
        }

        public void ChangeBgColor(object obj)
        {
            /*HERE I WANT TO CHANGE GRID COLOR*/
        }
    }
}

抱歉我的英语不好。

最好的问候。

Answer 1

最适合你应该实现 INotifyPropertyChanged在你的 ViewModel 中:

public class MainWindowViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    // This method is called by the Set accessor of each property.
    // The CallerMemberName attribute that is applied to the optional propertyName
    // parameter causes the property name of the caller to be substituted as an argument.
    private void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

然后，将 NotifyPropertyChanged() 添加到您的属性 setter 中。

好的。接下来，将带有网格背景颜色的新属性添加到 ViewModel:

private Brush _gridBackground;
public Brush GridBackground
{ 
    get { return _gridBackground; }
    set
    {
        _gridBackground = value;
        NotifyPropertyChanged();
    }
}

并将您的网格背景绑定(bind)到您的属性:

<Grid Background="{Binding GridBackground}">

最后，您可以在命令处理程序中更改 GridBackground:

public void ChangeBgColor(object obj)
{
    GridBackground = Brushes.Blue;
}

您应该记住，将 WPF 类(如 Brush)添加到您的代码中是一种不好的做法。更好的方法是使用 IValueConverter在您的 ViewModel 中的 XAML 代码和 BCL 类中。例如，您可以在 ViewModel 中使用枚举，然后在 ValueConverter 中将其转换为画笔。

1. 为 ViewModel 的属性添加新枚举:

   public enum GridState { Valid, Invalid }
   

2. 更改属性类型:

   private GridState _gridBackground;
   public GridState GridBackground
   { 
       get { return _gridBackground; }
       set
       {
           _gridBackground = value;
           NotifyPropertyChanged();
       }
   }
   

3. 添加带有值转换器的新类

   public class GridStateToBackgroundColorConverter : IValueConverter
   {
       #region IValueConverter Members
   
       public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
       {
           GridState val = (GridState) value;
           if(val == GridState.Valid)
               return Brushes.Green;
           return Brushes.Red;
       }
   
       public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
       {
           throw new NotSupportedException();
       }
   
       #endregion
   }
   

4. 向您的控件添加新的静态资源

    <UserControl.Resources>
        <converters:GridStateToBackgroundColorConverter x:Key="gridStateToBackgroundColorConverter" />
    </UserControl.Resources>
   

5. 更新绑定(bind)到您的属性

   <Grid Background="{Binding GridBackground, Converter={StaticResource gridStateToBackgroundColorConverter}">