类似ScrollView的写法，可实现子View的拖拽及复位到边界功能
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package com.fqxyi.utils.view;import android.content.Context;import android.support.annotation.Nullable;import android.support.v4.widget.ViewDragHelper;import android.util.AttributeSet;import android.view.MotionEvent;import android.view.View;import android.widget.FrameLayout;/** * 可拖拽ViewGroup，具体的View内容由调用者决定，但只能有一个直接孩子 * 参考文章：https://blog.csdn.net/lmj623565791/article/details/46858663 */public class DragLayout extends FrameLayout { private ViewDragHelper mDragHelper; //true left, false right private boolean leftOrRight; // private View child; public DragLayout(Context context) { super(context); init(); } public DragLayout(Context context, @Nullable AttributeSet attrs) { super(context, attrs); init(); } public DragLayout(Context context, @Nullable AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); init(); } private void init() { /** * @param ViewGroup forParent 必须是一个ViewGroup * @param float sensitivity 灵敏度 * @param Callback cb 回调 */ mDragHelper = ViewDragHelper.create(this, 1.0f, new ViewDragCallback()); } private class ViewDragCallback extends ViewDragHelper.Callback { /** * 尝试捕获子view，一定要返回true * * @param view 尝试捕获的view * @param pointerId 指示器id？ * 这里可以决定哪个子view可以拖动 */ @Override public boolean tryCaptureView(View view, int pointerId) { return view == child; } /** * 处理水平方向上的拖动 * * @param child 被拖动到view * @param left 移动到达的x轴的距离 * @param dx 建议的移动的x距离 */ @Override public int clampViewPositionHorizontal(View child, int left, int dx) { FrameLayout.LayoutParams params = (FrameLayout.LayoutParams) child.getLayoutParams(); // 两个if主要是为了让View在ViewGroup里面滑动 if (params == null) { if (getPaddingLeft() > left) { return getPaddingLeft(); } if (getWidth() - child.getWidth() - getPaddingRight() < left) { return getWidth() - child.getWidth() - getPaddingRight(); } } else { if (getPaddingLeft() + params.leftMargin > left) { return getPaddingLeft() + params.leftMargin; } if (getWidth() - child.getWidth() - getPaddingRight() - params.rightMargin < left) { return getWidth() - child.getWidth() - getPaddingRight() - params.rightMargin; } } return left; } /** * 处理竖直方向上的拖动 * * @param child 被拖动到view * @param top 移动到达的y轴的距离 * @param dy 建议的移动的y距离 */ @Override public int clampViewPositionVertical(View child, int top, int dy) { FrameLayout.LayoutParams params = (FrameLayout.LayoutParams) child.getLayoutParams(); // 两个if主要是为了让View在ViewGroup里面滑动 if (params == null) { if (getPaddingTop() > top) { return getPaddingTop(); } if (getHeight() - child.getHeight() - getPaddingBottom() < top) { return getHeight() - child.getHeight(); } } else { if (getPaddingTop() + params.topMargin > top) { return getPaddingTop() + params.topMargin; } if (getHeight() - child.getHeight() - getPaddingBottom() - params.bottomMargin < top) { return getHeight() - child.getHeight() - getPaddingBottom() - params.bottomMargin; } } return top; } /** * 手指释放的时候回调 */ @Override public void onViewReleased(View releasedChild, float xvel, float yvel) { FrameLayout.LayoutParams params = (FrameLayout.LayoutParams) releasedChild.getLayoutParams(); if (params == null) { if (leftOrRight) { mDragHelper.settleCapturedViewAt(getPaddingLeft(), (int) releasedChild.getY()); } else { mDragHelper.settleCapturedViewAt(getWidth() - releasedChild.getWidth() - getPaddingRight(), (int) releasedChild.getY()); } } else { if (leftOrRight) { mDragHelper.settleCapturedViewAt(getPaddingLeft() + params.leftMargin, (int) releasedChild.getY()); } else { mDragHelper.settleCapturedViewAt(getWidth() - releasedChild.getWidth() - getPaddingRight() - params.rightMargin, (int) releasedChild.getY()); } } invalidate(); } /** * 如果子View不消耗事件，那么整个手势（DOWN-MOVE*-UP）都是直接进入onTouchEvent，在onTouchEvent的DOWN的时候就确定了captureView。 * 如果消耗事件，那么就会先走onInterceptTouchEvent方法，判断是否可以捕获， * 而在判断的过程中会去判断另外两个回调的方法：getViewHorizontalDragRange和getViewVerticalDragRange，只有这两个方法返回大于0的值才能正常的捕获。 */ @Override public int getViewHorizontalDragRange(View child) { return getMeasuredWidth() - child.getMeasuredWidth(); } @Override public int getViewVerticalDragRange(View child) { return getMeasuredHeight() - child.getMeasuredHeight(); } /** * 当拖拽到状态改变时回调 * * @param state 新的状态 */ @Override public void onViewDragStateChanged(int state) { switch (state) { case ViewDragHelper.STATE_DRAGGING: // 正在被拖动 break; case ViewDragHelper.STATE_IDLE: // view没有被拖拽或者 正在进行fling/snap break; case ViewDragHelper.STATE_SETTLING: // fling完毕后被放置到一个位置 break; } super.onViewDragStateChanged(state); } } @Override public void computeScroll() { if (mDragHelper.continueSettling(true)) { invalidate(); } } @Override public boolean onInterceptTouchEvent(MotionEvent ev) { /** * 检查是否可以拦截touch事件 * 如果onInterceptTouchEvent可以return true 则这里return true */ return mDragHelper.shouldInterceptTouchEvent(ev); } @Override public boolean onTouchEvent(MotionEvent event) { switch (event.getAction()) { case MotionEvent.ACTION_DOWN: if (checkNeedIntercept(event)) { return true; } break; case MotionEvent.ACTION_UP: if (event.getX() >= getWidth() / 2) { leftOrRight = false; } else { leftOrRight = true; } break; } /** * 处理拦截到的事件 * 这个方法会在返回前分发事件 */ mDragHelper.processTouchEvent(event); return false; } /** * 如果view不在边上停靠时，触摸view需要拦截，否则会出现无法滑动的情况 */ private boolean checkNeedIntercept(MotionEvent event) { FrameLayout.LayoutParams params = (FrameLayout.LayoutParams) child.getLayoutParams(); if (params == null) { if (child.getX() - getPaddingLeft() != 0 && child.getX() + child.getWidth() + getPaddingRight() != getWidth()) { mDragHelper.processTouchEvent(event); return true; } } else { if (child.getX() - getPaddingLeft() - params.leftMargin != 0 && child.getX() + child.getWidth() + getPaddingRight() + params.rightMargin != getWidth()) { mDragHelper.processTouchEvent(event); return true; } } return false; } @Override protected void onFinishInflate() { super.onFinishInflate(); if (getChildCount() != 1) { throw new IllegalStateException("DragLayout can host only one direct child"); } child = getChildAt(0); child.setClickable(true); }}复制代码