Bitmaps Example

This example shows how to display a bitmap stored as a resource in the application package.

A screenshot of the application.

We begin by declaring a unique namespace for the package we are creating. This is typically based on the reversed form of a domain name and should be unique to this package.

__package__ = "com.example.bitmaps"

We import the classes and modules needed by our application. The most relevant to this example are the BitmapFactory, Canvas and Paint classes from the module which handle bitmap loading and painting. The Resources class from the android.content.res module is used to access the resources packaged with the application.

from android.content import Context
from android.content.res import Resources
from import BitmapFactory, Canvas, Paint
import android.os
import android.view

We import a class from the special app_resources module that is created when the application is built. This allows us to refer to the application resources.

from app_resources import R

The BitmapsActivity is derived from the standard Activity class and represents the application. Android will create an instance of this class when the user runs it.

The initialisation method simply calls the corresponding method in the base class.

class BitmapsActivity(

    def __init__(self):

The onCreate method is called when the activity is run. We call the corresponding method in the base class to help set up the activity before creating a custom view that we set as the activity's content view. The DrawView class is defined below.

    def onCreate(self, bundle):
   , bundle)
        view = DrawView(self, self.getResources())

The DrawView class is a custom view that is derived from the standard View class that simply draws a bitmap on a single colour background and responds to touches.

The initialisation method accepts the usual Context object as its first parameter. The second parameter is a Resources object that refers to the application's resources.

class DrawView(android.view.View):

    @args(void, [Context, Resources])
    def __init__(self, context, resources):

We initialise the view by calling the corresponding method in the base class, and we initialise some instance attributes to describe how the view will appear.

        android.view.View.__init__(self, context)
        self.paint = Paint()
        self.paint.setARGB(255, 40, 80, 160)
        self.x = 0
        self.y = 0
        self.bitmap = BitmapFactory.decodeResource(resources,

The bitmap is decoded from the data in the application's resources using a static method of the BitmapFactory class. This is stored as an instance attribute.

We reimplement the standard onDraw method to draw the custom content in the view. As usual, we call the corresponding method in the base class before painting the background and bitmap.

    def onDraw(self, canvas):
        android.view.View.onDraw(self, canvas)
        canvas.drawBitmap(self.bitmap, self.x, self.y, self.paint)

The onSizeChanged method is called when the size of the view has changed. We only take note of the size the first time this method is called - for this call the oldWidth and oldHeight values are zero.

    def onSizeChanged(self, width, height, oldWidth, oldHeight):
        if oldWidth == 0:
            self.x = width/2 - self.bitmap.getWidth()/2
            self.y = height/2 - self.bitmap.getHeight()/2

The onTouchEvent method is called when the user touches the screen. We respond to this by changing the position of the bitmap, redraw the view by calling the standard invalidate method and return True to indicate that we handled the event.

    def onTouchEvent(self, event):
        self.x = int(event.getX()) - self.bitmap.getWidth()/2
        self.y = int(event.getY()) - self.bitmap.getHeight()/2
        return True