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~~~~~~~~