通过画图实现动画效果

最近开始看Android的一些动画效果



总结下这两天的心得：



实现方法一 (参考 Asteroids 例子)





View 这个类有 onDraw(Canvas canvas) 方法 里面可以用来画图



onTouchEvent(MotionEvent event) 方法 用来实现触摸屏的事件



onKeyDown(int keyCode, KeyEvent event) 方法 用来实现键盘的事件



基本上就可以用2个方法实现画图



简单例子 触摸屏 event.getAction() == MotionEvent.ACTION_DOWN 时 获得坐标



float tx = event.getX();

float ty = event.getY();



然后调用invalidate() 方法就会刷新屏幕(也就是调用 onDraw(Canvas canvas) )





下面是一个实例(从apidemo 的例子中扒出来的~~~~)

package com.k;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BlurMaskFilter;
import android.graphics.Canvas;
import android.graphics.MaskFilter;
import android.graphics.Paint;
import android.graphics.Path;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;

public class Vi extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(new MyView(this));
}
public class MyView extends View {
private Paint mPaint;
private MaskFilter mBlur;

private Bitmap mBitmap;
private Canvas mCanvas;
private Path mPath;
private Paint mBitmapPaint;

public MyView(Context c) {
super(c);
mPaint = new Paint();
mPaint.setAntiAlias(true);
mPaint.setDither(true);
mPaint.setColor(0xFFFF0000);
mPaint.setStyle(Paint.Style.STROKE);
mPaint.setStrokeJoin(Paint.Join.ROUND);
mPaint.setStrokeCap(Paint.Cap.ROUND);
mPaint.setStrokeWidth(12);
mBlur = new BlurMaskFilter(8, BlurMaskFilter.Blur.NORMAL);
mPaint.setMaskFilter(mBlur);
mBitmap = Bitmap.createBitmap(320, 480, Bitmap.Config.ARGB_8888);
mCanvas = new Canvas(mBitmap);
mPath = new Path();
mBitmapPaint = new Paint(Paint.DITHER_FLAG);
}

@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
}

@Override
protected void onDraw(Canvas canvas) {
canvas.drawColor(0xFFAAAAAA);

canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);

canvas.drawPath(mPath, mPaint);
}

private float mX, mY;
private static final float TOUCH_TOLERANCE = 4;

private void touch_start(float x, float y) {
mPath.reset();
mPath.moveTo(x, y);
mX = x;
mY = y;
}
private void touch_move(float x, float y) {
float dx = Math.abs(x - mX);
float dy = Math.abs(y - mY);
if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
mX = x;
mY = y;
}
}
private void touch_up() {
mPath.lineTo(mX, mY);
// commit the path to our offscreen
mCanvas.drawPath(mPath, mPaint);
// kill this so we don't double draw
mPath.reset();
}

@Override
public boolean onTouchEvent(MotionEvent event) {
float x = event.getX();
float y = event.getY();

switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
touch_start(x, y);
invalidate();
break;
case MotionEvent.ACTION_MOVE:
touch_move(x, y);
invalidate();
break;
case MotionEvent.ACTION_UP:
touch_up();
invalidate();
break;
}
return true;
}
}
}







那么如何自动刷新呢？不可能只有用户操作才去刷新屏幕吧。。。。



那就调用postInvalidate()方法



/**
* Cause an invalidate to happen on a subsequent cycle through the
* event loop. Use this to invalidate the View from a non-UI thread.
* onDraw will be called sometime in the future.
*/



这个是一段解释



在一本书上看的例子就是 用一个TimerTask 去延迟执行postInvalidate 达到 自动刷新屏幕的



可以用TimerTask cancel 方法 取消这个定时



实现方法二 (参考Snake例子)



用Handler实现



具体可以去看APIdemo里面的Snake的例子



刚才把Snake的例子 看了一遍 也自己做了个简单的动画的例子
发现 只用handler 就可以了
可以不用Runnable
postDelayed(runnable , delayMillis)
sendMessageDelayed(msg, delayMillis)

如果调用postDelayed 那就需要 Runnable
如果调用sendMessageDelayed 就不需要 Runnable



暂停handler 只要不在send Message 那就就不会触发handler了









其他的关于动画的实现慢慢补充~~~~~~~~