Car animation rotating wheels

Question

I am working in an app that shows different cars and the user needs to choose one. When you press on next the car moves out of the screen and the new one comes in.

My resources are:

• Car's body
• Car's wheel

(I need them to be separated because when the car moves I need to rotate the wheels)

I wanted to avoid AbsoluteLayout so my CarView extends `RelativeLayout. Here's the code:

public class CarView extends RelativeLayout {

    private ImageView mBody;
    private ImageView mLeftWheel;
    private ImageView mRightWheel;
    private float mScale;

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

    public CarView(Context context) {
        super(context);
    }

    public void initView(Car car) {
        mScale = getContext().getResources().getDisplayMetrics().density;
        Context ctx = getContext();
        RelativeLayout.LayoutParams params;

        params = new RelativeLayout.LayoutParams(LayoutParams.WRAP_CONTENT,
                LayoutParams.WRAP_CONTENT);
        params.addRule(RelativeLayout.CENTER_IN_PARENT);
        mBody = new ImageView(ctx);
        mBody.setLayoutParams(params);
        mBody.setImageResource(R.drawable.car_body);
        addView(mBody);

        params = new RelativeLayout.LayoutParams(LayoutParams.WRAP_CONTENT,
                LayoutParams.WRAP_CONTENT);
        params.addRule(RelativeLayout.CENTER_IN_PARENT);
        mLeftWheel = new ImageView(ctx);
        mLeftWheel.setLayoutParams(params);
        mLeftWheel.setImageResource(R.drawable.car_wheel);
        mLeftWheel.setPadding(0, dpToPx(79), dpToPx(188), 0);
        addView(mLeftWheel);


        params = new RelativeLayout.LayoutParams(LayoutParams.WRAP_CONTENT,
                LayoutParams.WRAP_CONTENT);
        params.addRule(RelativeLayout.CENTER_IN_PARENT);
        mRightWheel = new ImageView(ctx);
        mRightWheel.setLayoutParams(params);
        mRightWheel.setImageResource(R.drawable.car_wheel);
        mRightWheel.setPadding(dpToPx(203), dpToPx(75), 0, 0);
        addView(mRightWheel);
    }

    public void startMoving() {

        RotateAnimation rotateAnimation = new RotateAnimation(0, 360, Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF, 0.5f);
        rotateAnimation.setInterpolator(new LinearInterpolator());
        rotateAnimation.setDuration(900L);
        rotateAnimation.setRepeatCount(Animation.INFINITE);

        mLeftWheel.startAnimation(rotateAnimation);
        mRightWheel.startAnimation(rotateAnimation);
    }

    private int dpToPx(float dp) {
        return (int) (dp * mScale + 0.5f);
    }
}

Basically what I am doing is placing the body of the car and then using padding to place the wheels where they should be.

After reading this android developer's thread I notice that RotateAnimation rotates the whole view including the padding making the wheels to do some strange movement.

How should I fix this? Can you think of a better way to place the wheels ImageView instead of using padding?

Another issue I have is that in a certain point I want the wheels to stop moving, but the method cancel() in Animation is Since: API Level 8 and I need this to work on 1.5. How should I stop the rotation?

Answer 1

Can you think of a better way to place the wheels ImageView instead of using padding?

The "right answer", I think, is to create your own layout manager. Leastways, that's what we've been told. I tried it once and couldn't get it to work.

The not-quite-so-right answer may be margins rather than padding -- I haven't tried animating a View with margins and so I do not know if margins rotate. Padding should rotate, since that is considered "inside" the widget.

The even-less-right answer is to use a transparent View as a shim, rather than margins or padding. Align your ImageView relative to the shim with no margins or padding, with the shim's size set to position your ImageView where you want it.

The well-if-you-know-how answer is to dump the widgets entirely and just draw it all using the Canvas and 2D graphics APIs. Angry Birds, for example, presumably does not use ImageViews.