WPF和MVVM：动态将UserControl绑定到XAML

Question

seems like a trivial task: i am building a wpf application, using MVVM pattern. what i want is dynamically change part of a view, using different UserControls, dependent on user input.

let's say, i have got 2 UserControls, one with a button, and another with a label. in main view i have a container for that. following XAML "works":

<GroupBox Header="container" >
    <local:UserControlButton />
</GroupBox>

and a UserControl element with buttons pops up. if i change it to another one, it works too. question is how to feed that groupbox dynamically. if i put something like that in my model view:

private UserControl _myControl;
public UserControl MyControl
{
    get
    {
        return _myControl;
    }
    set
    {
        _myControl= value;
        InvokePropertyChanged("MyControl");
    }
}

and change my view XAML to something like:

<GroupBox Header="container" >
    <ItemsControl ItemsSource="{Binding MyControl}" />
</GroupBox>

and feed it from command with usercontrol for button or for label: nothing happens, although "MyControl" variable is set and is "invoke property changed"..

Answer 1

Obviously there are many ways to skin this particular cat - but to answer the question of why it doesn't work you need to look into the ItemsSource property of ItemsControl on MSDN .

The items control is designed to show multiple items, provided through an IEnumerable passed to the ItemsSource property. You are passing a UserControl, so the binding will fail.

For your example, I would change the ItemsControl to a ContentControl and bind the content to your MyControl property. This should then work.

<GroupBox Header="container" >
    <ContentControl Content="{Binding MyControl}" />
</GroupBox>

However, I would strongly recommend looking into other ways of doing this - having a control in your VM breaks MVVM to my mind. Depending on what you are doing look at data templates - @Sheridan's link in the comments provides an great description of a way to do it.

Answer 2

Couldn't post this as a comment so adding as answer..

Have a look at this: Implementing an own "Factory" for reusing Views in WPF

It uses DataTemplates but doesn't require the DataTemplate section for each view. If you potentially have a lot of user controls/views you wish to display or you are reusing through multiple views or you are intending to actually dynamically generate a view (versus just loading an existing user control) then this might suite your needs.