自定义Viw之使用ViewDragHelper做条目的侧滑菜单

public class DragHelperView extends ViewGroup {

private static final String TAG = "DragHelperView";
private View mChildLeft;
private View mChildRight;
private ViewDragHelper mHelper;

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

public DragHelperView(Context context, AttributeSet attrs) {
super(context, attrs);
mHelper = ViewDragHelper.create(this , mCallback);

}

ViewDragHelper.Callback mCallback = new ViewDragHelper.Callback() {
/**
* @param child 点击到的孩子
* @param pointerId
* @return  false:不孩子允许拖动 true：允许孩子拖动
*/
@Override
public boolean tryCaptureView(View child, int pointerId) {
return true;
}

/**
* 在action_move的时候调用
* @param child 拖动的孩子
* @param left 拖动孩子左边位置的参考值
* @param dx
* @return 孩子最终左边的位置
*/
@Override
public int clampViewPositionHorizontal(View child, int left, int dx) {

int minLeft = 0 ;
int maxLeft = 0;
if (child == mChildLeft){
minLeft = -mChildRight.getWidth();
maxLeft = 0;
}else if (child == mChildRight){
minLeft = mChildLeft.getWidth() - mChildRight.getWidth();
maxLeft = mChildLeft.getWidth();
}

if (left < minLeft){
left = minLeft;
}else if (left > maxLeft){
left = maxLeft;
}

return left;
}

/**
* 在view位置发生变化的时候调用
* @param dx 孩子x轴移动的偏移量
* @param dy 孩子y轴移动的偏移量
*/
@Override
public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
if (changedView == mChildLeft){
mChildRight.layout(mChildRight.getLeft() + dx , 0 , mChildRight.getRight() + dx , mChildRight.getHeight());
}else if (changedView == mChildRight){
mChildLeft.layout(mChildLeft.getLeft() + dx , 0 , mChildLeft.getRight() + dx , mChildLeft.getHeight());
}
}

/**
* 在action_up是调用
* @param releasedChild
* @param xvel
* @param yvel
*/
@Override
public void onViewReleased(View releasedChild, float xvel, float yvel) {
//临界点
int middle = mChildLeft.getWidth() - mChildRight.getWidth()/2;

int finalLeft = 0;
if (mChildRight.getLeft() > middle){
finalLeft = mChildLeft.getWidth();
//                mHelper.smoothSlideViewTo(mChildLeft , 0 , 0);
isOpen = false;
}else {
finalLeft = mChildLeft.getWidth() - mChildRight.getWidth();
//                mHelper.smoothSlideViewTo(mChildLeft , -mChildRight.getWidth() , 0);
isOpen = true;
}

mHelper.smoothSlideViewTo(mChildRight , finalLeft , 0);
invalidate();//触发重新绘制

}
};

boolean isOpen = false;

public boolean isOpen(){
return isOpen;
}

@Override
public void computeScroll() {
super.computeScroll();
//continueSettling(true):返回值为true，表示滚动动画还没有结束
if (mHelper.continueSettling(true)){
//触发重新绘制
//            invalidate();
postInvalidate(); //在虚拟机上选中了Use Host GPU
//            ViewCompat.postInvalidateOnAnimation(this);//兼容各大厂商
}
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
mChildLeft = getChildAt(0);
mChildRight = getChildAt(1);

LayoutParams leftParams = mChildLeft.getLayoutParams();
int leftHeight = MeasureSpec.makeMeasureSpec(leftParams.height , MeasureSpec.EXACTLY);
mChildLeft.measure(widthMeasureSpec , leftHeight);

LayoutParams rightParams = mChildRight.getLayoutParams();
int rightWidth = MeasureSpec.makeMeasureSpec(rightParams.width , MeasureSpec.EXACTLY);

4000
int rightHeight = MeasureSpec.makeMeasureSpec(rightParams.height , MeasureSpec.EXACTLY);
mChildRight.measure(rightWidth , rightHeight);

//拆分大小
int measureWidth = MeasureSpec.getSize(widthMeasureSpec);
int measureHeight = MeasureSpec.getSize(heightMeasureSpec);
setMeasuredDimension(measureWidth , measureHeight);
}

@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
mChildLeft.layout(0 , 0, mChildLeft.getMeasuredWidth() , mChildLeft.getMeasuredHeight());
mChildRight.layout(mChildLeft.getWidth() , 0 , mChildLeft.getWidth() +
mChildRight.getMeasuredWidth() , mChildRight.getMeasuredHeight());

}

@Override
public boolean onTouchEvent(MotionEvent event) {
//触摸事件交给ViewDragHelper
mHelper.processTouchEvent(event);
return true;
}
}

<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent">

<com.myself.viewdraghelper.DragHelperView
android:layout_width="match_parent"
android:layout_height="80dp"
android:id="@+id/dh_container">

<include layout="@layout/child_left"/>

<include layout="@layout/child_right"/>

</com.myself.viewdraghelper.DragHelperView>
</LinearLayout>