How to redraw canvas in a view from activity

Question

I have a class that extends View and have the onDraw method implemented in my xml file I have a FrameLayout with my view and a RelativeLayout with a button

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
      android:layout_width="fill_parent"
      android:layout_height="fill_parent">
<canvas.pruebas.MyView
android:layout_width="fill_parent"
  android:layout_height="fill_parent"
/>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
     >
    <Button          
            android:id="@+id/btn"
            android:layout_width="100dp"           
            android:layout_height="wrap_content"
            android:text="hello"
            android:textSize="15sp"

            />
    </RelativeLayout>
</FrameLayout>

in my Activity class I want to implement when I click the button redraw the canvas in MyView class

public class CanvasActivity extends Activity {
    Button btn;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        btn=(Button)findViewById(R.id.btn);
        btn.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                //redraw canvas
            }
        });
    }
}

How Can I do that?

Solution

use invalidate().

First change your xml slightly to add an id:

<canvas.pruebas.MyView   android:id="@+id/mycanvasview"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
/>

then in code,

   ...
   btn.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            // get your view 
            canvas.pruebas.MyView myCanvas = (canvas.pruebas.MyView) findViewById(R.id.mycanvasview);
            //redraw canvas 
            myCanvas.invalidate();
        }
    });