wpf 带参数的 ICommand
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StackOverFlow
ICommand with Parameter
提问by Paul Gibson
I found this: Close Window from ViewModelwhich gets me started down the path of modifying my DelegateCommand class to handle parameters. But I am not able to get the syntax worked out.
我发现了这个：Close Window from ViewModel这让我开始修改我的 DelegateCommand 类来处理参数。但我无法解决语法问题。
Here is my DelegateCommand class, and the DelegateCommand class that I'm trying to create with little success:
这是我的 DelegateCommand 类，以及我尝试创建但收效甚微的 DelegateCommand 类：
public class DelegateCommand : ICommand
{
private readonly Action _action;
public DelegateCommand(Action action)
{
_action = action;
}
public void Execute(object parameter)
{
_action();
}
public bool CanExecute(object parameter)
{
return true;
}
#pragma warning disable 67
public event EventHandler CanExecuteChanged { add { } remove { } }
#pragma warning restore 67
}
public class DelegateCommand<T> : ICommand
{
private readonly Action _action;
public DelegateCommand(Action action)
{
_action = action;
}
public void Execute(object parameter)
{
_action();
}
public bool CanExecute(object parameter)
{
return true;
}
#pragma warning disable 67
public event EventHandler CanExecuteChanged { add { } remove { } }
#pragma warning restore 67
}
And here is what I do in the viewmodel:
这是我在视图模型中所做的：
public ICommand RowEditEndingAction
{
get { return new DelegateCommand(RowEditEnding); }
}
public ICommand UpdateDatabaseClick
{
get { return new DelegateCommand<object>(UpdateDatabase); } //THIS LINE HAS THE ERROR
}
And the actual method that will get called:
以及将被调用的实际方法：
public void UpdateDatabase(object parameter)
{
Window w = (Window)parameter;
// A bunch of stuff that works is removed for brevity
w.Close();
}
The compiler does not like my UpdateDatabaseClick, specifically saying there is something wrong with the arguments to DelegateCommand, but I am at a loss as to what I am doing wrong (though I am thinking it is syntax . . . ). What do I need to change? This all worked before I added the parameter to UpdateDatabase, and just had the DelegateCommand (no template class). But in that case I could not close the window.
编译器不喜欢我的 UpdateDatabaseClick，特别是说 DelegateCommand 的参数有问题，但我不知道我做错了什么（尽管我认为这是语法......）。我需要改变什么？在我将参数添加到 UpdateDatabase 之前，这一切都有效，并且只有 DelegateCommand（没有模板类）。但在那种情况下，我无法关闭窗户。
回答by O. R. Mapper
Here's the constructor of your DelegateCommand<T>class that you are calling:
这DelegateCommand<T>是您正在调用的类的构造函数：
public DelegateCommand(Action action)
And here is how you call it:
这是你如何称呼它的：
new DelegateCommand<object>(UpdateDatabase)
In there, UpdateDatabaseis declared as follows:
在那里，UpdateDatabase声明如下：
public void UpdateDatabase(object parameter)
Now, the constructor you are invoking expects an Action. That is a parameterlessmethod without a return value.
现在，您正在调用的构造函数需要一个Action. 这是一个没有返回值的无参数方法。
However, you are passing in a method with one parameter. That is what the compiler complains about.
但是，您传入的是一个带有一个参数的方法。这就是编译器所抱怨的。
What you actually probably want to do is to accept any method with one parameter- for that, you can use the type Action<T>. As your parameter should presumeably have the same type that is passed as a type argument to your DelegateCommand<T>class, you can declare your constructor like this:
您实际上可能想要做的是接受任何带有一个参数的方法- 为此，您可以使用 type Action<T>。由于您的参数大概应该具有作为类型参数传递给您的DelegateCommand<T>类的相同类型，您可以像这样声明您的构造函数：
public DelegateCommand(Action<T> action)
Now, you also need to update the type of your backing field where you store the action:
现在，您还需要更新存储操作的支持字段的类型：
private readonly Action<T> _action;
Lastly, as _actionnow expects an argument, you need to pass that argument when invoking _actionin DelegateCommand<T>.Execute. Normally, you want to hand over the parameterobject you receive as an argument to the Executemethod. However, that value is always typed to object, whereas you want to work with a strongly-typed value of type Tin your method. Therefore, you will also have to add an additional cast:
最后，正如_action现在期望的参数一样，您需要在调用_actionin时传递该参数DelegateCommand<T>.Execute。通常，您希望将parameter收到的对象作为Execute方法的参数传递。但是，该值始终键入为object，而您希望T在方法中使用类型为强类型的值。因此，您还必须添加额外的演员表：
public void Execute(object parameter)
{
_action((T)parameter);
}
回答by Thai Anh Duc
I suggest you try Prism framework. It has all the component, tools, you need to work with WPF application with MVVM model.
我建议你试试 Prism 框架。它拥有使用 MVVM 模型处理 WPF 应用程序所需的所有组件、工具。
