MVVM在点击时更改网格的背景颜色

Question

我是MVVM模式的真正初学者.我正试图在按钮的点击上更改网格的背景.我有一个包含按钮的网格的xaml,以及一个ViewModel .cs,我希望在按钮点击时更改网格的背景.直到我点击时才能成功显示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*/
        }
    }
}

对不起,我的英语不好.

最好的祝福.

Answer 1

最重要的是，您应该在 ViewModel 中实现INotifyPropertyChanged ：

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() 添加到属性设置器中。

好的。接下来，将带有网格背景颜色的新属性添加到 ViewModel 中：

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

并将网格的背景绑定到您的属性：

<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 Brush 等 WPF 类添加到代码中是一种不好的做法。更好的方法是在 XAML 代码中使用IValueConverter并在 ViewModel 中使用 BCL 类。例如，您可以在ViewModel中使用枚举，并在ValueConverter中将其转换为画笔。

1. 为您的 ViewModel 属性添加新的枚举：

   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. 使用值转换器添加新类

   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. 将新的静态资源添加到您的控件中

   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));
           }
       }
   }
   

5. 更新对您的属性的绑定

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