仿二手车之家的竖直拖动栏自定义View

大家好，本篇博客带来的一个效果是仿二手车之家的竖直拖动蓝的一个效果，具体如下:

为什么会选择写一个这样的效果呢？是因为这里牵涉到了两个知识点，一个是最近正在学习的事件分发，还有一个是ViewDragHelper这个拖拽的工具类。

首先 我们先实现这个一个拖拽的效果:

下面的红色的区域块，可以在竖直方向上拖动，当区域仅限于后面颜色的高度，话不多说，直接上代码:

/*** Created by DELL on 2017/9/12.* Description :*/public class VerticalDragView extends FrameLayout {private ViewDragHelper mDragHelper;private View mFirstView;private View mDragView;private int mFirstViewHeight;public VerticalDragView(@NonNull Context context) {this(context,null);}public VerticalDragView(@NonNull Context context, @Nullable AttributeSet attrs) {this(context, attrs,0);}public VerticalDragView(@NonNull Context context, @Nullable AttributeSet attrs, @AttrRes int defStyleAttr) {super(context, attrs, defStyleAttr);mDragHelper = ViewDragHelper.create(this,mCallback);}@Overrideprotected void onFinishInflate() {super.onFinishInflate();int childCount = getChildCount();if(childCount != 2){throw new RuntimeException("子Vview必须为两个view");}mFirstView = getChildAt(0);mDragView = getChildAt(1);}@Overrideprotected void onLayout(boolean changed, int left, int top, int right, int bottom) {super.onLayout(changed, left, top, right, bottom);//获取第一个子View的高度   方便后面判断只能在搞高度范围内被拖动mFirstViewHeight = mFirstView.getMeasuredHeight();Log.i("JUSTH","firstViewHeight=="+mFirstViewHeight);}//创建ViewDragHelper的callBack对象private ViewDragHelper.Callback mCallback = new ViewDragHelper.Callback() {/*** 返回true 代表能拖到   返回false  代表不能拖动* @param child* @param pointerId* @return*/@Overridepublic boolean tryCaptureView(View child, int pointerId) {//代表只有在拖动的view是第二个view的时候，才允许拖动return child == mDragView;}//当触摸释放时  会执行该方法/*** 当拖动距离大于firstView的一半高度是  打开  否则  关闭* @param releasedChild* @param xvel* @param yvel*/@Overridepublic void onViewReleased(View releasedChild, float xvel, float yvel) {if(mDragView.getTop() > mFirstViewHeight/2){mDragHelper.settleCapturedViewAt(0,mFirstViewHeight);}else if(mDragView.getTop() <= mFirstViewHeight/2){mDragHelper.settleCapturedViewAt(0,0);}invalidate();}//管理竖直方向上是否能被拖动 以及被拖动的范围@Overridepublic int clampViewPositionVertical(View child, int top, int dy) {if(top < 0){top = 0;}if(top>mFirstViewHeight){top = mFirstViewHeight;}return top;}};//相应drawerHelper中的释放滚动事件@Overridepublic void computeScroll() {if(mDragHelper.continueSettling(true)){invalidate();}}@Overridepublic boolean onTouchEvent(MotionEvent event) {mDragHelper.processTouchEvent(event);return true;}
}

好了，到这里，拖拽的效果就已经写完了!

下面，我们接着看，看二手车之家的效果，可以拖拽的部分，应该是一个类似ListView，RecycleView这样的一个效果，那我们们这里就有listView来代替吧，只要实现了事件的拦截与分发，不管使用哪种控件，都是一样的:

/*** Created by DELL on 2017/9/12.* Description :*/public class VerticalDragView extends FrameLayout {private ViewDragHelper mDragHelper;private View mFirstView;private View mDragView;private int mFirstViewHeight;private boolean isFirstViewOpen = false;public VerticalDragView(@NonNull Context context) {this(context,null);}public VerticalDragView(@NonNull Context context, @Nullable AttributeSet attrs) {this(context, attrs,0);}public VerticalDragView(@NonNull Context context, @Nullable AttributeSet attrs, @AttrRes int defStyleAttr) {super(context, attrs, defStyleAttr);mDragHelper = ViewDragHelper.create(this,mCallback);}@Overrideprotected void onFinishInflate() {super.onFinishInflate();int childCount = getChildCount();if(childCount != 2){throw new RuntimeException("子Vview必须为两个view");}mFirstView = getChildAt(0);mDragView = getChildAt(1);}@Overrideprotected void onLayout(boolean changed, int left, int top, int right, int bottom) {super.onLayout(changed, left, top, right, bottom);//获取第一个子View的高度   方便后面判断只能在搞高度范围内被拖动mFirstViewHeight = mFirstView.getMeasuredHeight();Log.i("JUSTH","firstViewHeight=="+mFirstViewHeight);}//创建ViewDragHelper的callBack对象private ViewDragHelper.Callback mCallback = new ViewDragHelper.Callback() {/*** 返回true 代表能拖到   返回false  代表不能拖动* @param child* @param pointerId* @return*/@Overridepublic boolean tryCaptureView(View child, int pointerId) {//代表只有在拖动的view是第二个view的时候，才允许拖动return child == mDragView;}//当触摸释放时  会执行该方法/*** 当拖动距离大于firstView的一半高度是  打开  否则  关闭* @param releasedChild* @param xvel* @param yvel*/@Overridepublic void onViewReleased(View releasedChild, float xvel, float yvel) {if(mDragView.getTop() > mFirstViewHeight/2){mDragHelper.settleCapturedViewAt(0,mFirstViewHeight);isFirstViewOpen = true;}else if(mDragView.getTop() <= mFirstViewHeight/2){mDragHelper.settleCapturedViewAt(0,0);isFirstViewOpen = false;}invalidate();}//管理竖直方向上是否能被拖动 以及被拖动的范围@Overridepublic int clampViewPositionVertical(View child, int top, int dy) {if(top < 0){top = 0;}if(top>mFirstViewHeight){top = mFirstViewHeight;}return top;}};//相应drawerHelper中的释放滚动事件@Overridepublic void computeScroll() {if(mDragHelper.continueSettling(true)){invalidate();}}@Overridepublic boolean onTouchEvent(MotionEvent event) {mDragHelper.processTouchEvent(event);return true;}int downY;@Overridepublic boolean onInterceptTouchEvent(MotionEvent ev) {//当第一个view打开的时候  拦截事件if(isFirstViewOpen){return true;}//当listView下拉的时候，当其可见的最上面一个条目是第一条 且该listview在最上端的时候 拦截事件switch (ev.getAction()){case MotionEvent.ACTION_DOWN:downY = (int) ev.getY();mDragHelper.processTouchEvent(ev);break;case MotionEvent.ACTION_MOVE:if((ev.getY() - downY)>0 && !canChildScrollUp()){return true;}break;}return super.onInterceptTouchEvent(ev);}private boolean isFirst(){ListView listView = (ListView) mDragView;return listView.getFirstVisiblePosition() == 0;}public boolean canChildScrollUp() {if (android.os.Build.VERSION.SDK_INT < 14) {if (mDragView instanceof AbsListView) {final AbsListView absListView = (AbsListView) mDragView;return absListView.getChildCount() > 0&& (absListView.getFirstVisiblePosition() > 0 || absListView.getChildAt(0).getTop() < absListView.getPaddingTop());} else {return ViewCompat.canScrollVertically(mDragView, -1) || mDragView.getScrollY() > 0;}} else {return ViewCompat.canScrollVertically(mDragView, -1);}}
}

效果如下:（虽然可能是丑了点，但毕竟效果是有了）

好了，今天就到这里吧!