Question

我是MVVM模式的真正初学者。我试图在按钮的点击上更改网格的背景。我有一个包含一个按钮的网格的xaml，以及一个ViewModel .cs，我想在那里更改按钮点击的网格背景。直到那里，当我点击时，我才能成功显示一个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

您应该在ViewModel中实现INotifyPropertyChanged：

ko

然后，将NotifyPropertyChanged（）添加到属性设置器。

确定。接下来，将带有网格背景颜色的新Property添加到ViewModel：

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));
        }
    }
}

将你的网格背景绑定到你的财产：

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

最后，您只需在命令处理程序中更改GridBackground：

<Grid Background="{Binding GridBackground}">

你应该记住，在你的代码中添加像Brush这样的WPF类是不好的做法。更好的方法是在XAML代码中使用IValueConverter，在ViewModel中使用BCL类。例如，您可以在ViewModel中使用枚举，并将其转换为ValueConverter中的画笔。

为ViewModel的属性添加新枚举：

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

更改属性类型：

public enum GridState { Valid, Invalid }

使用值转换器添加新类

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

向控件添加新的静态资源

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
}

更新与您的媒体资源的绑定

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

Answer 2

如果要更改网格背景颜色，则可以使用命令参数。您可以将任何UI控件作为Command参数传递。在您的情况下，传递网格以访问视图模型中的网格。将名称赋给网格并使用该名称作为命令参数。为此，您需要实现如下代码：

<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 Name="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}"
        CommandParameter="{Binding Elementname="grid"}"/>
</Grid>

对.xaml文件进行此更改后。实现参数化中继命令以使用此传递的Grid在Viewmodel文件中使用。实现参数化中继命令尝试实现以下代码：

    private ICommand m_ButtonCommand;
    public ICommand ButtonCommand
    {
        get
        {
            return m_ButtonCommand;
        }
        set
        {
            m_ButtonCommand = value;
        }
    }

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

    public void ChangeBgColor(Grid grid)
    {
        if(grid!=null)
            grid.Background = Brushes.Red; //Any color you want to change.
    }

我希望这会奏效。谢谢。

MVVM在点击时改变网格的背景颜色

2 个答案: