How to draw using an xml layout in android

I am trying to work through an android example given on the developers' page. It gives 2 ways of drawing on a canvas. The first way is to use a class called CustomDrawableView, which looks like this:

public class CustomDrawableView extends View {
private ShapeDrawable mDrawable;

public CustomDrawableView(Context context) {
super(context);

int x = 10;
int y = 10;
int width = 300;
int height = 50;

mDrawable = new ShapeDrawable(new OvalShape());
mDrawable.getPaint().setColor(0xff74AC23);
mDrawable.setBounds(x, y, x + width, y + height);
}

protected void onDraw(Canvas canvas) {
mDrawable.draw(canvas);
}
}

This is then called by the main class:

CustomDrawableView mCustomDrawableView;
protected void onCreate(Bundle savedInstanceState) {    
super.onCreate(savedInstanceState);    
mCustomDrawableView = new CustomDrawableView(this);        
setContentView(mCusto开发者_如何学编程mDrawableView);
}

But then the tutorial says:

If you'd like to draw this custom drawable from the XML layout instead of from the Activity, then the CustomDrawable class must override the View(Context, AttributeSet) constructor, which is called when instantiating a View via inflation from XML. Then add a CustomDrawable element to the XML, like so:

<com.example.shapedrawable.CustomDrawableView
   android:layout_width="fill_parent"     
android:layout_height="wrap_content"     
/>

I have successfully got the first example to run but I do not know what my code should look like if I want to adopt the second option. Presumably, I start with @Override View but then I am stuck.

The reason I want to do this is because I want to create a canvas that covers only part of the screen so I can fit buttons and text in the other part.

If the tutorial is correct then the only change you make is to add that constructor. You probably want to move the drawable init code to a separate method.

public CustomDrawableView(Context context, AttributeSet attrs) {
    super(context, attrs);
    initDrawable();
}

The xml

<com.example.shapedrawable.CustomDrawableView
   android:id="+id/custom_drawable_view"
   android:layout_width="fill_parent"     
    android:layout_height="wrap_content"     
/>

And you can obtain the view like this.

CustomDrawableView mCustomDrawableView;

protected void onCreate(Bundle savedInstanceState) {    
    super.onCreate(savedInstanceState);          
    setContentView(R.layout.main); // assuming your layout is named main.xml
    mCustomDrawableView = (CustomDrawableView) findViewById(R.id.custom_drawable_view);
}

public CustomDrawableView(Context v,AttributeSet as){ super(v,as); drawShape(as); } public void drawShape(AttributeSet ast) {
int x =0; int y=0 ; int width=0; int height=0 ;

            x=Integer.parseInt(ast.getAttributeValue(null, "x"));       
    y=Integer.parseInt(ast.getAttributeValue(null, "y"));
    width=Integer.parseInt(ast.getAttributeValue(null, "width"));
    height= Integer.parseInt(ast.getAttributeValue(null, "height"));

    mDrawable = new ShapeDrawable(new OvalShape());
    mDrawable.getPaint().setColor(0xff74AC23);
    mDrawable.setBounds(x, y, x + width, y + height);

} }

MainActivity.java{ CustomDrawableView mCustomDrawableView;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
 }
public View.OnClickListener cc = (new View.OnClickListener() {
    public void onClick(View view) {
                    setContentView(R.id.myid);}
       });       

} This works fine..(Not so sure whether this is the best way to do it...)