PullToZoomInLayout

package com.myluffy.util.im2;

import android.animation.ValueAnimator;
import android.content.Context;
import android.content.res.TypedArray;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ScrollView;

/**
 * 下拉放大指定{@link PullToZoomInLayout#mZoomInView} View
 */
public class PullToZoomInLayout extends ScrollView {

    private int mDownY;

    // 被放大view原始的高
    private int mZoomInViewInitialHeight;

    // 被放大的view
    private View mZoomInView;

    // 被放大view的ID
    private final int mZoomInID;

    // 被放大view的布局参数
    private ViewGroup.LayoutParams mZoomInViewLP;

    public PullToZoomInLayout(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        TypedArray t = getContext().obtainStyledAttributes(attrs, R.styleable.Pull);
        mZoomInID = t.getResourceId(R.styleable.Pull_pull_id, -1);
        t.recycle();
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        if (mZoomInView == null) {
            return super.onInterceptTouchEvent(ev);
        }

        switch (ev.getAction()) {
            case MotionEvent.ACTION_DOWN:
                mDownY = (int) ev.getY();
                break;
            case MotionEvent.ACTION_MOVE:
                if (getScrollY() == 0) {
                    if (ev.getY() - mDownY > 0) {
                        return true;
                    }
                }
                break;
        }
        return super.onInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        if (mZoomInView == null) {
            return super.onTouchEvent(ev);
        }

        // 超出屏幕.
        if (ev.getY() >= getHeight()) {
            restoreLayout();
            return true;
        }

        switch (ev.getAction()) {
            case MotionEvent.ACTION_MOVE:
                if (getScrollY() == 0) {
                    int offset = (int) ((ev.getY() - mDownY) * 0.5);
                    if (offset > 0) {
                        mZoomInViewLP.height = mZoomInViewInitialHeight + offset;
                        mZoomInView.setLayoutParams(mZoomInViewLP);
                        return true;
                    }
                }
                break;

            case MotionEvent.ACTION_UP:
                restoreLayout();
                break;
        }

        return super.onTouchEvent(ev);
    }

    private void restoreLayout() {
        if (mZoomInViewLP.height > mZoomInViewInitialHeight) {
            ValueAnimator anim = ValueAnimator.ofInt(mZoomInViewLP.height, mZoomInViewInitialHeight)
                    .setDuration(300);
            anim.start();
            anim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {

                @Override
                public void onAnimationUpdate(ValueAnimator animation) {
                    mZoomInViewLP.height = (int) animation.getAnimatedValue();
                    mZoomInView.setLayoutParams(mZoomInViewLP);
                }
            });
        }
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        if (mZoomInID != -1) {
            mZoomInView = findViewById(mZoomInID);
            mZoomInView.post(new Runnable() {
                @Override
                public void run() {
                    mZoomInViewInitialHeight = mZoomInView.getHeight();
                }
            });
        }
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldW, int oldH) {
        if (mZoomInView != null) {
            mZoomInViewLP = mZoomInView.getLayoutParams();
        }
    }
}