解析下拉图片放大

原理：

生成一个FrameLayout，然后装载ImageView，在手指按下的时候设置初始值mLastMotionY、mActivePointerId、mMaxScale、mLastScale；在手指移动的时候动态的改变localLayoutParams.height；当手指抬起时，生成一个Runnable，设置缩放动画，更改localLayoutParams.height

public class PullToZoomListView extends ListView implements AbsListView.OnScrollListener {
    private static final int INVALID_VALUE = -1;
    private static final String TAG = "PullToZoomListView";
    private static final Interpolator sInterpolator = new Interpolator() {//缩放减速
        public float getInterpolation(float paramAnonymousFloat) {
            float f = paramAnonymousFloat - 1.0F;//下拉-1 - 0
            Log.e("getInterpolation", "f | " + f);
            return 1.0F + f * (f * (f * (f * f)));
        }
    };
    int mActivePointerId = -1;
    private FrameLayout mHeaderContainer;//头部布局容器
    private int mHeaderHeight;//头部控件的高度
    private ImageView mHeaderImage;
    float mLastMotionY = -1.0F;//监听手指在Y轴的移动
    float mLastScale = -1.0F;//下拉：-1 - 2
    float mMaxScale = -1.0F;//3
    private AbsListView.OnScrollListener mOnScrollListener;
    private ScalingRunnalable mScalingRunnalable;//缩放动画
    private int mScreenHeight;//屏幕高度
    private ImageView mShadow;

    public PullToZoomListView(Context paramContext) {
        super(paramContext);
        init(paramContext);
    }

    public PullToZoomListView(Context paramContext,
                              AttributeSet paramAttributeSet) {
        super(paramContext, paramAttributeSet);
        init(paramContext);
    }

    public PullToZoomListView(Context paramContext, AttributeSet paramAttributeSet, int paramInt) {
        super(paramContext, paramAttributeSet, paramInt);
        init(paramContext);
    }

    //手抬起时，设置缩放动画时间
    private void endScraling() {
        Log.e(TAG, "endScraling");
        if (this.mHeaderContainer.getBottom() >= this.mHeaderHeight)
            this.mScalingRunnalable.startAnimation(200L);
    }

    private void init(Context paramContext) {
        DisplayMetrics localDisplayMetrics = new DisplayMetrics();
        ((Activity) paramContext).getWindowManager().getDefaultDisplay().getMetrics(localDisplayMetrics);
        this.mScreenHeight = localDisplayMetrics.heightPixels;
        this.mHeaderContainer = new FrameLayout(paramContext);//生成一个FrameLayout，装载下面两个ImageView

        this.mHeaderImage = new ImageView(paramContext);
        int i = localDisplayMetrics.widthPixels;//屏幕宽度（像素）
        setHeaderViewSize(i, (int) (9.0F * (i / 16.0F)));
        this.mShadow = new ImageView(paramContext);
        FrameLayout.LayoutParams localLayoutParams = new FrameLayout.LayoutParams(-1, -2);
        localLayoutParams.gravity = 80;
        this.mShadow.setLayoutParams(localLayoutParams);

        this.mHeaderContainer.addView(this.mHeaderImage);
        this.mHeaderContainer.addView(this.mShadow);
        addHeaderView(this.mHeaderContainer);

        this.mScalingRunnalable = new ScalingRunnalable();//生成一个缩放动画
        super.setOnScrollListener(this);
    }


    private void onSecondaryPointerUp(MotionEvent paramMotionEvent) {
        Log.e(TAG, "onSecondaryPointerUp = " + paramMotionEvent.getAction() + "");
        int i = (paramMotionEvent.getAction()) >> 8;
        if (paramMotionEvent.getPointerId(i) == this.mActivePointerId)
            if (i != 0) {
                int j = 1;
                this.mLastMotionY = paramMotionEvent.getY(0);
                this.mActivePointerId = paramMotionEvent.getPointerId(0);
                return;
            }
    }

    //重置参数
    private void reset() {
        this.mActivePointerId = -1;
        this.mLastMotionY = -1.0F;
        this.mMaxScale = -1.0F;
        this.mLastScale = -1.0F;
    }

    public ImageView getHeaderView() {
        return this.mHeaderImage;
    }

    public boolean onInterceptTouchEvent(MotionEvent paramMotionEvent) {
        return super.onInterceptTouchEvent(paramMotionEvent);
    }

    //
    protected void onLayout(boolean paramBoolean, int paramInt1, int paramInt2, int paramInt3, int paramInt4) {
        super.onLayout(paramBoolean, paramInt1, paramInt2, paramInt3, paramInt4);
        Log.e(TAG, "onLayout " + " mHeaderHeight == " + this.mHeaderContainer.getHeight());
        if (this.mHeaderHeight == 0)
            this.mHeaderHeight = this.mHeaderContainer.getHeight();
    }

    //正在滚动 ; 上滑启动
    @Override
    public void onScroll(AbsListView paramAbsListView, int paramInt1, int paramInt2, int paramInt3) {
        Log.e(TAG, "onScroll");
        float f = this.mHeaderHeight - this.mHeaderContainer.getBottom();
        Log.e(TAG, "f|" + f + " mHeaderContainer.getBottom()|" + this.mHeaderContainer.getBottom());
        if ((f > 0.0F) && (f < this.mHeaderHeight)) {
            Log.e(TAG, "1");
            int i = (int) (0.65D * f);
            this.mHeaderImage.scrollTo(0, -i);
        } else if (this.mHeaderImage.getScrollY() != 0) {
            Log.e(TAG, "2");
            this.mHeaderImage.scrollTo(0, 0);
        }
        if (this.mOnScrollListener != null) {
            this.mOnScrollListener.onScroll(paramAbsListView, paramInt1, paramInt2, paramInt3);
        }
    }

    //滚动状态完成后
    public void onScrollStateChanged(AbsListView paramAbsListView, int paramInt) {
        if (this.mOnScrollListener != null)
            this.mOnScrollListener.onScrollStateChanged(paramAbsListView, paramInt);
    }

    public boolean onTouchEvent(MotionEvent ev) {
        Log.e(TAG, "MotionEvent == " + (0xFF & ev.getAction()));

        switch (ev.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_OUTSIDE:
            case MotionEvent.ACTION_DOWN:
                if (!this.mScalingRunnalable.mIsFinished) {
                    this.mScalingRunnalable.abortAnimation();
                }
                this.mLastMotionY = ev.getY();//触摸时y轴的点
                this.mActivePointerId = ev.getPointerId(0);//0
                this.mMaxScale = (this.mScreenHeight / this.mHeaderHeight);//屏幕高度/头部控件的高度
                this.mLastScale = (this.mHeaderContainer.getBottom() / this.mHeaderHeight);//504/504
                break;
            case MotionEvent.ACTION_MOVE:
                int j = ev.findPointerIndex(this.mActivePointerId);//id永远为0
                if (j == -1) {
                    Log.e(TAG, "Invalid pointerId=" + this.mActivePointerId + " in onTouchEvent");
                } else {
                    if (this.mLastMotionY == -1.0F)
                        this.mLastMotionY = ev.getY(j);

                    if (this.mHeaderContainer.getBottom() >= this.mHeaderHeight) {//mHeaderHeight = 405
                        ViewGroup.LayoutParams localLayoutParams = this.mHeaderContainer.getLayoutParams();
                        float f = ((ev.getY(j) - this.mLastMotionY + this.mHeaderContainer.getBottom()) / this.mHeaderHeight - this.mLastScale) / 2.0F + this.mLastScale;
                        //下拉：f从1.0 - 2.0
                        Log.e(TAG, "localLayoutParams.height = " + localLayoutParams.height + " localLayoutParams.width = " + localLayoutParams.width + " f = " + f);

                        if ((this.mLastScale <= 1.0D) && (f < this.mLastScale)) {
                            localLayoutParams.height = this.mHeaderHeight;
                            this.mHeaderContainer.setLayoutParams(localLayoutParams);
                            return super.onTouchEvent(ev);
                        }
                        this.mLastScale = Math.min(Math.max(f, 1.0F), this.mMaxScale);
                        localLayoutParams.height = ((int) (this.mHeaderHeight * this.mLastScale));
                        if (localLayoutParams.height < this.mScreenHeight)
                            this.mHeaderContainer.setLayoutParams(localLayoutParams);
                        this.mLastMotionY = ev.getY(j);
                        return true;
                    }
                    this.mLastMotionY = ev.getY(j);
                }
                break;
            case MotionEvent.ACTION_UP:
                reset();
                endScraling();
                break;
            case MotionEvent.ACTION_CANCEL:
                int i = ev.getActionIndex();
                this.mLastMotionY = ev.getY(i);
                this.mActivePointerId = ev.getPointerId(i);
                break;
            case MotionEvent.ACTION_POINTER_DOWN://设置多点触控
                onSecondaryPointerUp(ev);
                this.mLastMotionY = ev.getY(ev.findPointerIndex(this.mActivePointerId));
                break;
            case MotionEvent.ACTION_POINTER_UP:
        }
        return super.onTouchEvent(ev);
    }

    //初始化头部控件的布局
    public void setHeaderViewSize(int paramInt1, int paramInt2) {
        Object localObject = this.mHeaderContainer.getLayoutParams();
        if (localObject == null)
            localObject = new AbsListView.LayoutParams(paramInt1, paramInt2);
        ((ViewGroup.LayoutParams) localObject).width = paramInt1;
        ((ViewGroup.LayoutParams) localObject).height = paramInt2;
        this.mHeaderContainer.setLayoutParams((ViewGroup.LayoutParams) localObject);
        this.mHeaderHeight = paramInt2;
    }

    //设置接收通知的侦听器，监听列表每次滚动。
    public void setOnScrollListener(
            AbsListView.OnScrollListener paramOnScrollListener) {
        this.mOnScrollListener = paramOnScrollListener;
    }


    //用线程缩放
    class ScalingRunnalable implements Runnable {
        long mDuration;//持续时间
        boolean mIsFinished = true;//动画是否结束
        float mScale;//缩放比例
        long mStartTime;//开始时间

        ScalingRunnalable() {
        }

        //终止动画
        public void abortAnimation() {
            this.mIsFinished = true;
        }

        //开始缩放
        public void run() {
            float f2;
            ViewGroup.LayoutParams localLayoutParams;
            if ((!this.mIsFinished) && (this.mScale > 1.0D)) {
                float f1 = ((float) SystemClock.currentThreadTimeMillis() - (float) this.mStartTime) / (float) this.mDuration;
                Log.e(TAG, "mTime" + " mStartTime = " + mStartTime + " ---- SystemClock.currentThreadTimeMillis() = " + SystemClock.currentThreadTimeMillis());
                f2 = this.mScale - (this.mScale - 1.0F) * PullToZoomListView.sInterpolator.getInterpolation(f1);
                localLayoutParams = PullToZoomListView.this.mHeaderContainer.getLayoutParams();
                if (f2 > 1.0F) {//下拉：f2==2 - 1   f1==0 - 1
                    Log.e(TAG, "f2>1.0" + " f2 = " + f2 + " ---- f1 = " + f1);
                    localLayoutParams.height = ((int) (f2 * PullToZoomListView.this.mHeaderHeight));//动态的控制这个参数，改变图片的变化
                    PullToZoomListView.this.mHeaderContainer.setLayoutParams(localLayoutParams);
                    PullToZoomListView.this.post(this);
                    return;
                }
                this.mIsFinished = true;
            }
        }

        //记录抬起手指的坐标，设置动画属性
        public void startAnimation(long paramLong) {
            this.mStartTime = SystemClock.currentThreadTimeMillis();
            this.mDuration = paramLong;
            this.mScale = ((float) (PullToZoomListView.this.mHeaderContainer.getBottom()) / PullToZoomListView.this.mHeaderHeight);
            Log.e("startAnimation", "--------------->mScale + " + mScale + "\nBottom = " + PullToZoomListView.this.mHeaderContainer.getBottom() + "\nmHeaderHeight = " + PullToZoomListView.this.mHeaderHeight);
            this.mIsFinished = false;
            PullToZoomListView.this.post(this);
        }
    }
}