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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