A Bouncing Ball - Basic Graphics Animation Demo

martin_nuke · by **martin_nuke** » Sat Dec 15, 2007 6:20 am

A Bouncing Ball - Bacic Graphics Animation Demo

What is this: This is a Basic Graphics Animation demo which uses a Thread and Canvas to display and animate a Drawable.

What it will look like:

Description:
There are two files the BounceActivity.java and the BounceView.java.

"src/your_package_structure/BounceActivity.java":

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package org.anddev.android.bouncingball;
 
import android.app.Activity;
import android.os.Bundle;
import android.view.Window;
import android.os.Handler;
import android.os.Message;
 
public class BounceActivity extends Activity {
 
        // Just a RANDOM ID to recognize a Message later
        protected static final int GUIUPDATEIDENTIFIER = 0x101;
 
        Thread myRefreshThread = null;
 
        /* Our 'ball' is located within this View */
        BounceView myBounceView = null;
 
        Handler myGUIUpdateHandler = new Handler() {
 
                // @Override
                public void handleMessage(Message msg) {
                        switch (msg.what) {
                                case BounceActivity.GUIUPDATEIDENTIFIER:
                                        /* Repaint the BounceView 
                                         * (where the ball is in) */
                                        myBounceView.invalidate();
                                        break;
                        }
                        super.handleMessage(msg);
                }
        };
 
        /** Called when the activity is first created. */
        @Override
        public void onCreate(Bundle icicle) {
                super.onCreate(icicle);
                // Set fullscreen
                this.requestWindowFeature(Window.FEATURE_NO_TITLE);
 
                // Create a
                this.myBounceView = new BounceView(this);
                this.setContentView(this.myBounceView);
 
                /* create a Thread that will 
                 * periodically send messages 
                 * to our Handler */
                new Thread(new RefreshRunner()).start();
        }
 
        class RefreshRunner implements Runnable {
                // @Override
                public void run() {
                        while (!Thread.currentThread().isInterrupted()) {
                                // Send Message to the Handler which will call the invalidate() method of the BOucneView
                                Message message = new Message();
                                message.what = BounceActivity.GUIUPDATEIDENTIFIER;
                                BounceActivity.this.myGUIUpdateHandler.sendMessage(message);
 
                                try {
                                        Thread.sleep(100); // a 10th of a second
                                } catch (InterruptedException e) {
                                        Thread.currentThread().interrupt();
                                }
                        }
                }
        }
}
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"src/your_package_structure/BounceView.java":

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package org.anddev.android.bouncingball;
 
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Point;
import android.graphics.drawable.Drawable;
import android.view.View;
 
public class BounceView extends View {
 
        /* Our Ball together with the location it will be painted*/
        protected Drawable mySprite;
        protected Point mySpritePos = new Point(0,0);
        
        /* Working with a Enum is 10000% 
         * safer than working with int's 
         * to 'remember' the direction. */
        protected enum HorizontalDirection {LEFT, RIGHT}
        protected enum VerticalDirection {UP, DOWN}
        protected HorizontalDirection myXDirection = HorizontalDirection.RIGHT;
        protected VerticalDirection myYDirection = VerticalDirection.UP;
 
 
        public BounceView(Context context) {
                super(context);
                // Set the background
                this.setBackground(this.getResources().getDrawable(R.drawable.icon));
                // Load our "Ball"
                this.mySprite = this.getResources().getDrawable(R.drawable.icon);
        }
 
        @Override
        protected void onDraw(Canvas canvas) {
                /* Check if the Ball started to leave 
                 * the screen on left or right side */
                if (mySpritePos.x >= this.getWidth() - mySprite.getBounds().width()) {
                        this.myXDirection = HorizontalDirection.LEFT;
                } else if (mySpritePos.x <= 0) {
                        this.myXDirection = HorizontalDirection.RIGHT;
                }
 
                /* Check if the Ball started to leave 
                 * the screen on bottom or upper side */
                if (mySpritePos.y >= this.getHeight() - mySprite.getBounds().height()) {
                        this.myYDirection = VerticalDirection.UP;
                } else if (mySpritePos.y <= 0) {
                        this.myYDirection = VerticalDirection.DOWN;
                }
 
                /* Move the ball left or right */
                if (this.myXDirection == HorizontalDirection.RIGHT) {
                        this.mySpritePos.x += 10;
                } else {
                        this.mySpritePos.x -= 10;
                }
                /* Move the ball up or down */
                if (this.myYDirection == VerticalDirection.DOWN) {
                        this.mySpritePos.y += 10;
                } else {
                        this.mySpritePos.y -= 10;
                }
 
                /* Set the location, where the sprite
                 * will draw itself to the canvas */
                this.mySprite.setBounds(this.mySpritePos.x, this.mySpritePos.y, 
                                this.mySpritePos.x + 50, this.mySpritePos.y + 50);
                
                /* Make the sprite draw itself to the canvas */
                this.mySprite.draw(canvas);
        }
}
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plusminus · by **plusminus** » Sat Dec 15, 2007 3:42 pm

Thx martin_nuke for posting that tutorial

I allowed myself to add some comments and some minor code-changes for improved understanding.

Best Regards,
plusminus

rock_win · by **rock_win** » Mon Jan 21, 2008 4:26 pm

What is the basic difference between sending a message to the handler and posting to a handler.

I'm unable to run my animation with the above code, however when i post it , it works fine.

plusminus · by **plusminus** » Mon Jan 21, 2008 4:52 pm

Hello rock_win,

you mean the difference between sendMessage(Message) and post(Runnable) :?:

Besides the parameters I would say none!

post(Runnable)
Causes the Runnable r to be added to the message queue. (The runnable will be run on the thread to which this handler is attached.)

vs.

sendMessage(Message)
Pushes a message onto the end of the message queue after all pending messages before the current time. It will be received in handleMessage(Message), in the thread attached to this handler.

Regards,
plusminus

tdi · by **tdi** » Sat Dec 27, 2008 1:57 pm

Im trying to base on this application to implement simple Life game. Ive got a problem with passing width and height of the canvas to my external LideEngine class.

I can see in bouncing ball that this.getWidth() and this.getHeight() is used. In my application im an trying to use it too but in the constructor but it returns 0. How can i pass width and hejgth to some external class?
this is my view (MyView.java) constructor:

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        public MyView(Context context) {
 
                super(context);
 
                alive.setColor(0xffffffff);
 
                le = new LifeEngine(this.getWidth(),this.getHeight());
 
        }
 
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Please note that im just strting with android this is my first draft application just to feel the sdk

tdi · by **tdi** » Sat Dec 27, 2008 5:12 pm

Ok I found solution myself:

The fact that width and height are 0 in constructor is normal, as these variables are visible after onSizeChanged is called. So for one to have proper values it has to Override the onSizeChanged method like that:

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        @Override
 
        protected void onSizeChanged(int w, int h, int oldw, int oldh) {
 
                super.onSizeChanged(w, h, oldw, oldh);
 
        }
 
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Timmeah · by **Timmeah** » Thu Feb 12, 2009 2:26 pm

I'm quite a n00b, so I'm sorry if this question is very stupid.

But it says the method is undefined. How and where can I define this?

Timmeah · by **Timmeah** » Thu Feb 12, 2009 3:00 pm

And this n00b has learned something.

this.setBackground should be changed to this.setBackgroundDrawable

Didn't know this

isaackearl · by **isaackearl** » Sun Mar 08, 2009 1:32 am

Hey,

great tutorial, I just have a simple quesiton. I have made a similiar program while learning to program in java for android... and I didn't use a seperate thread. I'm just wondering what the advantages are to using threads? fps?

thanks,
Isaac

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A Bouncing Ball - Basic Graphics Animation Demo

A Bouncing Ball - Basic Graphics Animation Demo

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