Android實現花瓣飄落效果的步驟

效果展示

實現原理

  • 首先需要生成繪制小花的坐標點,坐標點的橫坐標是根據控件的寬度隨機生成的,而縱坐標則設置為小花圖片高度的負值(這樣可以實現小花從屏幕外進入)。
  • 將這些點存儲到集合當中。
  • 遍歷集合根據點的位置繪制小花
  • 繪制完後不斷增加各個點的縱坐標

實現步驟

1.定義變量將變量初始化

    private SurfaceHolder mHolder;
    private boolean mFlag = true;//繪制小花線程的開關標志
    private ArrayList<PointF> mFlowers;//小花點的坐標集合
    private Random mRandom;//負責隨機數生成
    private Bitmap mBitmap;//小花的圖案

    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);
        //設置背景透明
        this.setZOrderOnTop(true);
        mHolder.setFormat(PixelFormat.TRANSLUCENT);

        mFlowers = new ArrayList<>();
        mRandom = new Random();

        mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.ic_hua);

    }

2.實現添加花朵坐標點的方法

/**
     * 添加花朵
     */
    private void addFlower(){
        PointF point = new PointF();
        point.x=mRandom.nextInt(getWidth());//根據控件寬度隨機生成X軸坐標
        point.y=-mBitmap.getHeight();//縱坐標設置為小花圖像的負值(產生從屏幕外進入的效果)
        mFlowers.add(point);//將坐標點添加進集合
    }

3.實現SurfaceHolder.Callback及Runnable接口

public class FlowerView extends SurfaceView implements SurfaceHolder.Callback,Runnable

4.在run方法中實現繪制邏輯

 @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(否則會殘留一些無用圖像)
                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;//修改雨滴線的縱坐標,使其看起來在下雨
                    pointF.y=pointF.y+i;
                }
                mHolder.unlockCanvasAndPost(canvas);
                addFlower();
                //當繪制點的縱坐標大於控件高度時,將該點移除
                if(mFlowers.size()>0&&pointF!=null&&pointF.y>=getHeight()){
                    mFlowers.remove(pointF);
                }

            }catch (Exception e){}
        }
    }

5.在SurfaceHolder.Callback的回調方法中開啟繪制線程

 @Override
    public void surfaceCreated(SurfaceHolder holder) {
        mFlag = true;//surface創建時將線程開關打開
        new Thread(this).start();//開啟線程繪制
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        mFlowers.clear();//當控件發生改變時清除之前的繪制點
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        mFlag = false;//當surface銷毀時關掉繪制線程
    }

完整代碼展示

public class FlowerView extends SurfaceView implements SurfaceHolder.Callback,Runnable{
    private SurfaceHolder mHolder;
    private boolean mFlag = true;//繪制小花線程的開關標志
    private ArrayList<PointF> mFlowers;//小花點的坐標集合
    private Random mRandom;//負責隨機數生成
    private Bitmap mBitmap;//小花的圖案

    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);
        //設置背景透明
        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;//修改雨滴線的縱坐標,使其看起來在下雨
                    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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