如何使用依赖项属性替换UserControl的构造函数中的参数？ [英] how to use dependency property to replace the parameter in the constructor of a UserControl?

问题描述

我注意到之前曾问过类似的问题，但我没有找到任何详细的示例。

我有一个winform程序，其构造函数有一个参数cn：

  public AddFailure（ProSimConnect cn）// winform中的构造函数
 {
 this.connection = cn; 
 InitializeComponent（）; 
 ... 
} 
  

现在我需要在UserControl中对其进行模拟在WPF中将其放入MainWindow中。

在MainWindow.xaml中：

 <边界...> 
< IOS：Core_System /> 
< / Border> 
  

我想这样做，但我知道不能，因为它不应该有任何参数：

  public Core_System（ProSimConnect cn）// UserControl中的构造函数
 {
 this.cn = connection; 
 InitializeComponent（）; 
 ... 
} 
  

因此，我尝试使用依赖项属性：

 公共局部类Core_System：UserControl 
 {
 ProSimConnect连接； 
 
 //依赖属性
 public ProSimConnect cn 
 {
 get {return（ProSimConnect）GetValue（connectionProperty）; } 
 set {SetValue（connectionProperty，value）; } 
} 
公共静态只读DependencyProperty connectionProperty = 
 DependencyProperty.Register（ cn，typeof（ProSimConnect），typeof（Core_System））; 
 
 // UserControl中的构造函数
 public Core_System（）
 {
 this.connection = cn; 
 InitializeComponent（）; 
 ... 
} 
 ... 
} 
  

它不起作用-报告空异常。我哪里错了？谢谢。

这是需要在UserControl的构造函数中使用参数的函数：

  Failure [] getSelectedFailures（）
 {
 return cn.getFailures（）。Where（failure => failure_name.Contains（failure.name））。ToArray（）; 
} 
  

我称之为的位置是：

 公共部分类Core_System：UserControl 
 {
 ... 
 private void button_Engine_1_On_Fire（对象发送者，RoutedEventArgs e）
 {
 ... 
 ArmedFailure.create（getSelectedFailures（））; 
} 
} 
  

解决方案

A

您可以从构造函数中移动任何使用 ProSimConnect 的代码。 UserControl 到依赖项属性回调：

 公共部分类Core_System ：UserControl 
 {
 ProSimConnect连接； 
 
 //依赖性属性
 public ProSimConnect cn 
 {
 get {return（ProSimConnect）GetValue（connectionProperty）; } 
 set {SetValue（connectionProperty，value）; } 
} 
公共静态只读DependencyProperty connectionProperty = 
 DependencyProperty.Register（ cn，typeof（ProSimConnect），typeof（Core_System），new PropertyMetadata（new PropertyChangedCallback（OnPropertySet））; 
 
私有静态无效OnPropertySet（DependencyObject d，DependencyPropertyChangedEventArgs e）
 {
 Core_System ctrl = d作为Core_System; 
 ctrl.connection = e.NewValue作为ProSimConnect; 
 // ... 
} 
 
 // UserControl中的构造函数
 public Core_System（）
 {
 InitializeComponent（）; 
} 
} 
  

只要将依赖项属性设置为一个值，就会调用该回调。 / p>

I noticed that similar questions have been asked before but I did not find any detailed examples.

I have a winform program, its constructor has a parameter cn:

    public AddFailure(ProSimConnect cn)// constructor in winform
    {
      this.connection = cn;
      InitializeComponent();
      ...
    }

Now I need to simulate it in a UserControl in WPF and put it into MainWindow.

In MainWindow.xaml:

   <Border ...>
   <IOS:Core_System/>
   </Border>

I want to do this but I know I can't because it shouldn't have any parameter:

    public Core_System(ProSimConnect cn)// constructor in UserControl
    {            
        this.cn = connection;
        InitializeComponent();
        ...
    }

Therefore I try to use dependency property:

 public partial class Core_System : UserControl
{
    ProSimConnect connection;

    //dependency property
    public ProSimConnect cn
    {
        get { return (ProSimConnect) GetValue(connectionProperty); }
        set { SetValue(connectionProperty, value); }
    }
    public static readonly DependencyProperty connectionProperty =
        DependencyProperty.Register("cn", typeof(ProSimConnect),typeof(Core_System));

  // constructor in UserControl
  public Core_System()
  {            
      this.connection = cn;
      InitializeComponent();
      ...
  }
      ...
}

It doesn't work - it reports "null" exception. Where am I wrong? Thanks.

This is the function that need to use the parameter in the constructor of the UserControl:

    Failure []getSelectedFailures()
    {
        return cn.getFailures().Where(failure => failure_name.Contains(failure.name)).ToArray();
    }

The location I call it is:

public partial class Core_System : UserControl
{
  ...
    private void button_Engine_1_On_Fire(object sender, RoutedEventArgs e)
    {
       ...
       ArmedFailure.create(getSelectedFailures());
    }
}

解决方案

A dependency property cannot be set before the constructor has returned.

You could move any code that uses ProSimConnect from the constructor of the UserControl to a dependency property callback:

public partial class Core_System : UserControl
{
    ProSimConnect connection;

    //dependency property
    public ProSimConnect cn
    {
        get { return (ProSimConnect)GetValue(connectionProperty); }
        set { SetValue(connectionProperty, value); }
    }
    public static readonly DependencyProperty connectionProperty =
        DependencyProperty.Register("cn", typeof(ProSimConnect), typeof(Core_System), new PropertyMetadata(new PropertyChangedCallback(OnPropertySet));

    private static void OnPropertySet(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        Core_System ctrl = d as Core_System;
        ctrl.connection = e.NewValue as ProSimConnect;
        //...
    }

    // constructor in UserControl
    public Core_System()
    {
        InitializeComponent();
    }
}

The callback will be invoked whenever the dependency property is set to a value.

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