Android: custom View with draw + xml layout

create custom View class:

public class MyCanvas extends View {

int x = 0;

public MyCanvas(Context context, AttributeSet attrs) {

super(context, attrs);

// TODO Auto-generated constructor stub

}

Paint paint = new Paint();

Rect rect = new Rect();

protected void onDraw(Canvas canvas){

paint.setColor(0xFF999999);

rect.set(x, 100, 200, 150);

canvas.drawRect(rect, paint);

}

public void move(){

x+=5;

this.invalidate(); // redraw

}

}

xml layout:

<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"

    android:paddingBottom="@dimen/activity_vertical_margin"

    android:paddingLeft="@dimen/activity_horizontal_margin"

    android:paddingRight="@dimen/activity_horizontal_margin"

    android:paddingTop="@dimen/activity_vertical_margin"

    tools:context=".MainActivity" android:id="@+id/layout1">

    <TextView

        android:id="@+id/textView1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="@string/hello_world" />

    <Button

        android:id="@+id/button1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignLeft="@+id/textView1"

        android:layout_below="@+id/textView1"

        android:layout_marginTop="21dp"

        android:text="Button" />

    <com.boon.MyCanvas

        android:id="@+id/myCanvas1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_alignParentLeft="true"

        android:layout_below="@+id/button1"

        android:background="#CCCCCC" />

</RelativeLayout>

MainActivity.java: 

public class MainActivity extends Activity implements View.OnClickListener{

Button b;

MyCanvas c;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

b = (Button)this.findViewById(R.id.button1);

b.setOnClickListener(this);

c = (MyCanvas) this.findViewById(R.id.myCanvas1);

}

@Override

public boolean onCreateOptionsMenu(Menu menu) {

// Inflate the menu; this adds items to the action bar if it is present.

getMenuInflater().inflate(R.menu.main, menu);

return true;

}

@Override

public void onClick(View v) {

// TODO Auto-generated method stub

c.move();

}

}