Android实现花瓣飘落效果的步骤

效果展示

实现原理 首先需要生成绘制小花的坐标点，坐标点的横坐标是根据控件的宽度随机生成的，而纵坐标则设置为小花图片高度的负值（这样可以实现小花从屏幕外进入）。 将这些点存储到集合当中。 遍历集合根据点的位置绘制小花 绘制完后不断增加各个点的纵坐标实现步骤

1.定义变量将变量初始化

private SurfaceHolder mHolder; private boolean mFlag = true;//绘制小花线程的开关标志 private ArrayList<PointF> mFlowers;//小花点的坐标集合 private Random mRandom;//负责随机数生成 private Bitmap mBitmap;//小花的图案 public FlowerView(Context context) {super(context);init(); } public FlowerView(Context context, AttributeSet attrs) {super(context, attrs);init(); } public FlowerView(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);init(); } private void init(){mHolder = getHolder();mHolder.addCallback(this);//设置背景透明this.setZOrderOnTop(true);mHolder.setFormat(PixelFormat.TRANSLUCENT);mFlowers = new ArrayList<>();mRandom = new Random();mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.ic_hua); }

2.实现添加花朵坐标点的方法

/** * 添加花朵 */ private void addFlower(){PointF point = new PointF();point.x=mRandom.nextInt(getWidth());//根据控件宽度随机生成X轴坐标point.y=-mBitmap.getHeight();//纵坐标设置为小花图像的负值（产生从屏幕外进入的效果）mFlowers.add(point);//将坐标点添加进集合 }

3.实现SurfaceHolder.Callback及Runnable接口

public class FlowerView extends SurfaceView implements SurfaceHolder.Callback,Runnable

4.在run方法中实现绘制逻辑

@Override public void run() {while (mFlag){ try {Thread.sleep(80);//控制小花的下落速度Canvas canvas = mHolder.lockCanvas();PointF pointF = null;//清屏操作（否则会残留一些无用图像）if(canvas!=null){ canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);}else { continue;}for(PointF point: mFlowers){ pointF = point; canvas.drawBitmap(mBitmap,pointF.x,pointF.y,null); int i = mRandom.nextInt(getHeight()/50)+getHeight()/50;//修改雨滴线的纵坐标，使其看起来在下雨 pointF.y=pointF.y+i;}mHolder.unlockCanvasAndPost(canvas);addFlower();//当绘制点的纵坐标大于控件高度时，将该点移除if(mFlowers.size()>0&&pointF!=null&&pointF.y>=getHeight()){ mFlowers.remove(pointF);} }catch (Exception e){}} }

5.在SurfaceHolder.Callback的回调方法中开启绘制线程

@Override public void surfaceCreated(SurfaceHolder holder) {mFlag = true;//surface创建时将线程开关打开new Thread(this).start();//开启线程绘制 } @Override public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {mFlowers.clear();//当控件发生改变时清除之前的绘制点 } @Override public void surfaceDestroyed(SurfaceHolder holder) {mFlag = false;//当surface销毁时关掉绘制线程 }完整代码展示

public class FlowerView extends SurfaceView implements SurfaceHolder.Callback,Runnable{ private SurfaceHolder mHolder; private boolean mFlag = true;//绘制小花线程的开关标志 private ArrayList<PointF> mFlowers;//小花点的坐标集合 private Random mRandom;//负责随机数生成 private Bitmap mBitmap;//小花的图案 public FlowerView(Context context) {super(context);init(); } public FlowerView(Context context, AttributeSet attrs) {super(context, attrs);init(); } public FlowerView(Context context, AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);init(); } private void init(){mHolder = getHolder();mHolder.addCallback(this);//设置背景透明this.setZOrderOnTop(true);mHolder.setFormat(PixelFormat.TRANSLUCENT);mFlowers = new ArrayList<>();mRandom = new Random();mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.ic_hua); } @Override public void surfaceCreated(SurfaceHolder holder) {mFlag = true;new Thread(this).start(); } @Override public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {mFlowers.clear(); } @Override public void surfaceDestroyed(SurfaceHolder holder) {mFlag = false; } @Override public void run() {while (mFlag){ try {Thread.sleep(80);Canvas canvas = mHolder.lockCanvas();PointF pointF = null;//清屏操作if(canvas!=null){ canvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR);}else { continue;}for(PointF point: mFlowers){ pointF = point; canvas.drawBitmap(mBitmap,pointF.x,pointF.y,null); int i = mRandom.nextInt(getHeight()/50)+getHeight()/50;//修改雨滴线的纵坐标，使其看起来在下雨 pointF.y=pointF.y+i;}mHolder.unlockCanvasAndPost(canvas);addFlower();if(mFlowers.size()>0&&pointF!=null&&pointF.y>=getHeight()){ mFlowers.remove(pointF);} }catch (Exception e){}} } /** * 添加花朵 */ private void addFlower(){PointF point = new PointF();point.x=mRandom.nextInt(getWidth());point.y=-mBitmap.getHeight();mFlowers.add(point); }}

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