How to use Xamarin Forms Custom Button Renderer's Touch event to change the Buttons Image

问题

I figured it out. For anyone needing this. Please see the following. After Watching Xamarin Evolve a million times I caught on.

class LoginButtonCustomRenderer : ButtonRenderer
{
    protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.Button> e)
    {
        base.OnElementChanged(e);

        Android.Widget.Button thisButton = Control as Android.Widget.Button;

        thisButton.Touch += (object sender, TouchEventArgs e2) =>
        {
            if (e2.Event.Action == MotionEventActions.Down)
            {

                System.Diagnostics.Debug.WriteLine("TouchDownEvent");

                // Had to use the e.NewElement
                e.NewElement.Image = "pressed.png";
            }
            else if (e2.Event.Action == MotionEventActions.Up)
            {
                System.Diagnostics.Debug.WriteLine("TouchUpEvent");
            }
        };

    }

}

回答1:

you need call

Control.CallOnClick();

回答2:

Here is a sample how to implement a two state ImageButton in Xamarin Forms:

PCL:

public class FancyButton : Button
{
    public void SendClickedCommand()
    {
        ICommand command = this.Command;
        if (command != null)
        {
            command.Execute(this.CommandParameter);
        }
    }
}

Android render:

public class FancyButtonAndroid : ButtonRenderer
{
    Android.Widget.Button thisButton;

    protected override void OnElementChanged(ElementChangedEventArgs<Xamarin.Forms.Button> e)
    {
        base.OnElementChanged(e);
        thisButton = Control as Android.Widget.Button;
        thisButton.SetBackgroundResource(Resource.Drawable.btn_unpress);
        thisButton.Touch += ThisButton_Touch;
        thisButton.Click += HandleButtonClicked;
    }

    private void ThisButton_Touch(object sender, TouchEventArgs e)
    {
        e.Handled = false;
        if (e.Event.Action == MotionEventActions.Down)
        {
            System.Diagnostics.Debug.WriteLine("TouchDownEvent");
            thisButton.SetBackgroundResource(Resource.Drawable.btn_press);
        }
        else if (e.Event.Action == MotionEventActions.Up)
        {
            System.Diagnostics.Debug.WriteLine("TouchUpEvent");
            thisButton.SetBackgroundResource(Resource.Drawable.btn_unpress);
        }
    }

    private void HandleButtonClicked(object sender, EventArgs e)
    {
        if (Element != null && Element is FancyButton)
        {
            (Element as FancyButton).SendClickedCommand();
        }
    }

    protected override void Dispose(bool disposing)
    {
        if (thisButton != null)
        {
            thisButton.Touch -= ThisButton_Touch;
            thisButton.Click -= HandleButtonClicked;
        }
        base.Dispose(disposing);
    }
}

Note: in the Touch event set: e.Handled = false; to cause the Click event to rise.

来源：https://stackoverflow.com/questions/37255469/how-to-use-xamarin-forms-custom-button-renderers-touch-event-to-change-the-butt

标签

xaml

Xamarin

custom-controls