Question

我尝试使用单击事件的命令绑定按下按钮来更改画布的颜色，以避免MyView.xaml.cs文件中的任何代码。该命令正在激活，并且消息框在更改之前和之后显示正确的颜色代码值，因此设置了新颜色但画布的颜色不会更改。如果使用单击事件和MyView.xaml.cs中的代码后面的所有工作正常但我想在MyView.xaml.cs文件中使用命令绑定并且没有代码。我怎么能这样做，我做得不对的是什么？

MainWindow.xaml

public class Jdbcdemo {

    public static void main(String[] args) {
       try
       {
           //loading the jdbc driver
            Class.forName("com.mysql.jdbc.Driver").newInstance();
           //get a connection to database
           Connection myConn=DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbctry","your username","your password");
           //create a statement
           Statement stmt=myConn.createStatement();
           //execute sql query
           ResultSet rs=stmt.executeQuery("select * from employee");
           //process the result
           while(rs.next())
           {
               System.out.println(rs.getString("name")+" = "+rs.getString(1));
           }          
       }
       catch(SQLException e)
       {
           System.out.println(e);   
       }
       catch(Exception e)
       {
           System.out.println(e);
       }
    }

}

MyView.xaml文件

<Window x:Class="WpfApp1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:View="clr-namespace:WpfApp1.View"
    xmlns:ViewModel="clr-namespace:WpfApp1.ViewModel"
    mc:Ignorable="d"
    Title="MainWindow" Height="350" Width="525" Background="YellowGreen" 
    WindowStartupLocation="CenterScreen">

  <Window.DataContext>
    <ViewModel:MyClass/>
  </Window.DataContext>

  <View:MyView/>
</Window>

MyClass.cs

<UserControl x:Class="WpfApp1.View.MyView"
         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
         xmlns:ViewModel="clr-namespace:WpfApp1.ViewModel"
         xmlns:View="clr-namespace:WpfApp1.View">

  <Canvas Name="MainCanvas" Height="300" Width="502" Background="#FF148B63">
    <Button Name="ChangeColorButton" Command="{Binding CommandChangeColor}" Content="new color" Height="25" Width="55" Margin="225,268,225,10"/>
  </Canvas> 
</UserControl>

Answer 1

由于您可以拥有许多UserControl实例，MyClass如何知道它应该更新哪个MainCanvas实例？与CommandChangeColor的绑定类似，您还应该将Background绑定到MyClass中的某些属性。类似的东西：

的Xaml：

<Canvas Name="MainCanvas" Height="300" Width="502" Background="{Binding BackGroundColor}">
  <Button Name="ChangeColorButton" Command="{Binding CommandChangeColor}" Content="new color" Height="25" Width="55" Margin="225,268,225,10"/>
</Canvas>

MyClass.cs

public SolidColorBrush BackGroundColor {get;set;}

public void ChangeColor()
{
   MessageBox.Show("Color before: " + MainCanvas.Background.ToString());

   Random rnd = new Random();
   int i = rnd.Next(_listOfColors.Count - 1);
   BackGroundColor = new SolidColorBrush(_listOfColors[i]);

   MessageBox.Show("Color after: " + MainCanvas.Background.ToString());
}

您可能还想实现INotifyPropertyChanged。

从另一个类改变颜色不起作用

1 个答案: