DampView阻尼效果

阻尼效果即是图片向下拉动时会放大，松开会回弹

1.自定义一个DampView类，继承ScrollView

2.布局最外层必须是DampView,且DampView和要拉动的图片之间只能有一层layout（切记）

3.Activity中调用

import android.content.Context;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.widget.ImageView;
import android.widget.ScrollView;
import android.widget.Scroller;

/**
 * 阻尼效果的scrollview
 */
public class DampView extends ScrollView {
    /** 该属性具体参数 怎么控制  未解！！！！*/
    private static final int LEN = 0xc8;
    /** 回弹时所用的时间 */
    private static final int DURATION = 200;
    // private static final int MAX_DY = 200;
    /** 最大Y坐标 其值一般设定为Scroller对应控件的高度 */
    private static final int MAX_DY = 200;
    private Scroller mScroller;
    TouchTool tool;
    int left, top;
    float startX, startY, currentX, currentY;
    int imageViewH;
    int rootW, rootH;
    ImageView imageView;
    boolean scrollerType;

    public DampView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

    }

    public DampView(Context context, AttributeSet attrs) {
        super(context, attrs);
        mScroller = new Scroller(context);
    }

    public DampView(Context context) {
        super(context);

    }

    public void setImageView(ImageView imageView) {
        this.imageView = imageView;
    }

    float curY;
    @Override
    public boolean dispatchTouchEvent(MotionEvent event) {
        int action = event.getAction();
        if (!mScroller.isFinished()) {
            return super.onTouchEvent(event);
        }
        currentX = event.getX();
        currentY = event.getY();
        imageView.getTop();
        switch (action) {
            case MotionEvent.ACTION_DOWN:// 变量赋初始值
                left = imageView.getLeft();
                top = imageView.getBottom();
                rootW = getWidth();
                rootH = getHeight();

                imageViewH = imageView.getHeight();
                startX = currentX;
                startY = currentY;
                tool = new TouchTool(imageView.getLeft(), imageView.getBottom(),
                        imageView.getLeft(), imageView.getBottom() + LEN);
                break;
            case MotionEvent.ACTION_MOVE:
                if (imageView.isShown() && imageView.getTop() >= 0) {
                    if (tool != null) {
                        int t = tool.getScrollY(currentY - startY);
                        if (t >= top && t <= imageView.getBottom() + LEN) {
                            android.view.ViewGroup.LayoutParams params = imageView
                                    .getLayoutParams();
                            params.height = t;// 改变高度
                            imageView.setLayoutParams(params);
                        }

                    }
                    scrollerType = false;
                }
                break;
            case MotionEvent.ACTION_UP:
                scrollerType = true;

                // 松手后 回弹
                // 开始一个动画控制，由(startX , startY)在duration时间内前进(dx,dy)个单位
                // ，即到达坐标为(startX+dx , startY+dy)处
                mScroller.startScroll(imageView.getLeft(), imageView.getBottom(),
                        0 - imageView.getLeft(),
                        imageViewH - imageView.getBottom(), DURATION);
                invalidate();
                break;
        }

        return super.dispatchTouchEvent(event);
    }

    // //该mScroller针对于imageView的变化
    // 被父视图调用，用于必要时候对其子视图的值（mScrollX和mScrollY）
    // 进行更新。典型的情况如：父视图中某个子视图使用一个Scroller对象来实现滚动操作，会使得此方法被调用。
    @Override
    public void computeScroll() {
        if (mScroller.computeScrollOffset()) {
            int x = mScroller.getCurrX();
            int y = mScroller.getCurrY();// ImageView的当前Y坐标
            imageView.layout(0, 0, x + imageView.getWidth(), y);//使imageView本身做相应变化
            invalidate();

            // 滑动还未完成时，手指抬起时，当前y坐标大于其实imageView的高度时
            //设定imageView的布局参数  作用：使除imageView之外的控件做相应变化
            if (!mScroller.isFinished() && scrollerType && y > MAX_DY) {
                android.view.ViewGroup.LayoutParams params = imageView
                        .getLayoutParams();
                params.height = y;
                imageView.setLayoutParams(params);
            }
//                invalidate();
        }
    }

    public class TouchTool {

        private int startX, startY;

        public TouchTool(int startX, int startY, int endX, int endY) {
            super();
            this.startX = startX;
            this.startY = startY;
        }

        public int getScrollX(float dx) {
            int xx = (int) (startX + dx / 2.5F);
            return xx;
        }

        public int getScrollY(float dy) {
            int yy = (int) (startY + dy / 2.5F);//手势滑动距离/2.5 才是屏幕滑动的距离  此内部类主要做此用
            return yy;
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<de.hdodenhof.damp.DampView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/dampview"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical" >

        <!--此处必须设置imageview的scaleType为centerCrop,当然在代码中设置也可以-->
        <ImageView
            android:id="@+id/img"
            android:layout_width="match_parent"
            android:layout_height="200dp"
            android:scaleType="centerCrop"
            android:src="@drawable/bg_geren" />

    </LinearLayout>

</de.hdodenhof.damp.DampView>

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {

    private ImageView img;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        setupView();
    }

    public void setupView() {
        img = (ImageView) findViewById(R.id.img);
        DampView view = (DampView) findViewById(R.id.dampview);
        view.setImageView(img);
    }
}