ElasticScrollView.java

package cn.scau.scautreasure.widget;

import android.R;
import android.content.Context;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.view.MotionEvent;
import android.view.View;
import android.view.animation.Animation;
import android.view.animation.AnimationUtils;
import android.view.animation.TranslateAnimation;
import android.widget.ScrollView;
import org.androidannotations.annotations.EView;
import org.androidannotations.annotations.RootContext;

/**
 * 仿ios弹性 scrollView;
 *
 * User: special
 * Date: 13-9-3
 * Time: 下午9:30
 * Mail: specialcyci@gmail.com
 */
@EView
public class ElasticScrollView extends ScrollView {

    private View inner;
    private float y;
    private Context ctx;
    private Rect normal = new Rect();
    private boolean animationFinish = true;

    public ElasticScrollView(Context context) {
        super(context);
        this.ctx = context;
    }

    public ElasticScrollView(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.ctx = context;
    }

    public ElasticScrollView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        this.ctx = context;
    }


    @Override
    protected void onFinishInflate() {
        if (getChildCount() > 0) {
            inner = getChildAt(0);
        }
    }

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

    public void commOnTouchEvent(MotionEvent ev) {
        if (animationFinish) {
            int action = ev.getAction();
            switch (action) {
                case MotionEvent.ACTION_DOWN:
                    y = ev.getY();
                    super.onTouchEvent(ev);
                    break;
                case MotionEvent.ACTION_UP:
                    y = 0;
                    if (isNeedAnimation()) {
                        animation();
                    }
                    super.onTouchEvent(ev);
                    break;
                case MotionEvent.ACTION_MOVE:
                    final float preY = y == 0 ? ev.getY() : y;
                    float nowY = ev.getY();
                    int deltaY = (int) (preY - nowY);

                    y = nowY;
                    // 当滚动到最上或者最下时就不会再滚动，这时移动布局
                    if (isNeedMove()) {
                        if (normal.isEmpty()) {
                            // 保存正常的布局位置
                            normal.set(inner.getLeft(), inner.getTop(), inner.getRight(), inner.getBottom());
                        }
                        // 移动布局
                        inner.layout(inner.getLeft(), inner.getTop() - deltaY / 2, inner.getRight(), inner.getBottom() - deltaY / 2);
                    } else {
                        super.onTouchEvent(ev);
                    }
                    break;
                default:
                    break;
            }
        }
    }

    // 开启动画移动

    public void animation() {
        // 开启移动动画
        TranslateAnimation ta = new TranslateAnimation(0, 0, 0, normal.top - inner.getTop());
        ta.setInterpolator(AnimationUtils.loadInterpolator(ctx,
                R.anim.decelerate_interpolator));

        ta.setDuration(200);
        ta.setAnimationListener(new Animation.AnimationListener() {
            @Override
            public void onAnimationStart(Animation animation) {
                animationFinish = false;

            }

            @Override
            public void onAnimationRepeat(Animation animation) {

            }

            @Override
            public void onAnimationEnd(Animation animation) {
                inner.clearAnimation();
                // 设置回到正常的布局位置
                inner.layout(normal.left, normal.top, normal.right, normal.bottom);
                normal.setEmpty();
                animationFinish = true;
            }
        });
        inner.startAnimation(ta);
    }

    // 是否需要开启动画
    public boolean isNeedAnimation() {
        return !normal.isEmpty();
    }

    // 是否需要移动布局
    public boolean isNeedMove() {
        int offset = inner.getMeasuredHeight() - getHeight();
        int scrollY = getScrollY();
        if (scrollY == 0 || scrollY == offset) {
            return true;
        }
        return false;
    }

}