How do I pass the Button as CommandParameter from XAML in a Xamarin.Forms Page?

问题

I would like to pass a Xamarin.Forms.Button in it's own Command as the CommandParameter to my ViewModel. I know how to achieve this from the code behind e.g. ...

XAML (with most properties missed out for brevity)

<Button x:Name="myButton"
    Text="My Button"
    Command="{Binding ButtonClickCommand}"/>

XAML.cs

public partial class MyTestPage
{
    public MyTestPage()
    {
        InitializeComponent();

        myButton.CommandParameter = myButton;
    }
}

ViewModel

public class MyViewModel : ViewModelBase
{
    public MyViewModel()
    {
        ButtonClickCommand = new Command(
            (parameter) =>
            {
                var view = parameter as Xamarin.Forms.Button;
                if (view != null)
                {
                    // Do Stuff
                }
            });
    }

    public ICommand ButtonClickCommand { get; private set; }
}

... BUT is it possible to declare the CommandParameter in the XAML itself? Or in other words what is the binding syntax to set the parameter to the button itself?

<Button x:Name="myButton"
        Text="My Button"
        Command="{Binding ButtonClickCommand}"
        CommandParameter="{[WHAT WOULD GO HERE]}"/>

btw I've already tried CommandParameter="{Binding RelativeSource={RelativeSource Self}}" and that didn't work.

Thanks,

回答1:

Xamarin.Forms has a Reference markup extension that does just that:

<Button x:Name="myButton"
    Text="My Button"
    Command="{Binding ButtonClickCommand}"
    CommandParameter="{x:Reference myButton}"/>

Although, this is the first time I'm seeing this need, and you probably can better separate your Views from your ViewModels and solve this by using a cleaner pattern, or by not sharing a command across buttons.

回答2:

 <Button x:Name="myButton"
        Text="My Button"
        Command="{Binding ButtonClickCommand}"
        CommandParameter="{x:Reference myButton}"/>

In your ViewModel

public YourViewModel()
{
    ButtonClickCommand= new Command(ButtonClicked);
}

private async void ButtonClicked(object sender)
{
    var view = sender as Xamarin.Forms.Button;
}

回答3:

<Button x:Name="myButton"
    Text="My Button"
    Command="{Binding ButtonClickCommand}"
    CommandParameter={Binding RelativeSource=
                               {RelativeSource
                                Mode=FindAncestor,
                                AncestorType={x:Type Button}}/>

Should work, but im still at a loss why you need the button? The point of MVVM is to seperate Data and UI. everything you should need todo to the button can be done via DataBindings.

If the above doesnt work, the only other thing to try is to give the button an x:Key and CommandParamter = {StaticResource 'x:Key'}

来源：https://stackoverflow.com/questions/25912091/how-do-i-pass-the-button-as-commandparameter-from-xaml-in-a-xamarin-forms-page

标签

xaml

xamarin.forms

commandparameter