自定义ScrollView实现可拖出边界的效果



我们经常看到这样的效果,一个ListView和GridView亦或者是RecycleView,再上拉或下拉到顶部的时候,还能再拖拽一段距离,这种效果是是非常常见的,因为用的比较多,所以记录一下. 
 
实现思路是自定义一个ScrollView: 
具体代码如下

package fenganoschina.fenganoschina;

import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.animation.TranslateAnimation;
import android.widget.ListView;
import android.widget.ScrollView;

/**
 * 可以拖动的ScrollView
 */
public class CustomerScrollView extends ScrollView {

    private static final int size = 4;//拖动的距离为屏幕的高度的1/4
    private View inner;
    private float y;
    private Rect normal = new Rect();;

    public CustomerScrollView(Context context) {
        super(context);
    }

    public CustomerScrollView(Context context, AttributeSet attrs) {
        super(context, attrs);
        setOverScrollMode(ListView.OVER_SCROLL_NEVER);
    }

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

    @SuppressLint("ClickableViewAccessibility")
    @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) {
        int action = ev.getAction();
        switch (action) {
        case MotionEvent.ACTION_DOWN:
            y = ev.getY();
            break;
        case MotionEvent.ACTION_UP:
            if (isNeedAnimation()) {
                // Log.v("mlguitar", "will up and animation");
                animation();
            }
            break;
        case MotionEvent.ACTION_MOVE:
            final float preY = y;
            float nowY = ev.getY();
            /**
             * size=4 表示 拖动的距离为屏幕的高度的1/4
             */
            int deltaY = (int) (preY - nowY) / size;
            // 滚动
            // scrollBy(0, deltaY);

            y = nowY;
            if (isNeedMove()) {
                if (normal.isEmpty()) {
                    normal.set(inner.getLeft(), inner.getTop(),
                            inner.getRight(), inner.getBottom());
                    return;
                }
                int yy = inner.getTop() - deltaY;

                // 移动布局
                inner.layout(inner.getLeft(), yy, inner.getRight(),
                        inner.getBottom() - deltaY);
            }
            break;
        default:
            break;
        }
    }

    public void animation() {
        TranslateAnimation ta = new TranslateAnimation(0, 0, inner.getTop(),
                normal.top);
        ta.setDuration(200);
        inner.startAnimation(ta);
        inner.layout(normal.left, normal.top, normal.right, normal.bottom);
        normal.setEmpty();
    }

    public boolean isNeedAnimation() {
        return !normal.isEmpty();
    }

    public boolean isNeedMove() {
        int offset = inner.getMeasuredHeight() - getHeight();
        int scrollY = getScrollY();
        if (scrollY == 0 || scrollY == offset) {
            return true;
        }
        return false;
    }

}

 

布局文件

 

需要注意的是:因为涉及到ScrollView和ListView的嵌套,会导致ListView上显示数据不完全 
可以简单的自定义ListView代码: 
代码如下:

import android.content.Context;
import android.util.AttributeSet;
import android.widget.ListView;
/**
 * Created by cl
 */
public class ListViewForSc extends ListView{
    public ListViewForSc(Context context) {
        super(context);
    }

    public ListViewForSc(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    public ListViewForSc(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

        heightMeasureSpec = MeasureSpec.makeMeasureSpec(Integer.MAX_VALUE>>2, MeasureSpec.AT_MOST);
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }
}