AndroidSwipeLayout的使用(listview,gridview,view中滑动显示隐藏按钮的使用)

首先感谢类库作者。

这个控件比较强大，强大之处就在于SwipeLayout这个类

SwipeLayout：

里面封装了对拖动事件的处理类ViewDragHelper，以及内嵌了两个参数类，使用了枚举类：

public static enum DragEdge {
Left, Right, Top, Bottom;
};

public static enum ShowMode {
LayDown, PullOut
}

DragEdge类枚举了按钮从上下左右哪个位置出现。ShowMode类枚举了按钮是以被拉出的，还是隐藏在底部显示出来的。

默认是使用DragEdge.Right.ordinal()，ShowMode.PullOut.ordinal()，就是从右边拉出

构造函数：

public SwipeLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
mDragHelper = ViewDragHelper.create(this, mDragHelperCallback);
mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();

TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.SwipeLayout);
int dragEdgeChoices = a.getInt(R.styleable.SwipeLayout_drag_edge, DRAG_RIGHT);
mEdgeSwipesOffset[DragEdge.Left.ordinal()] = a.getDimension(R.styleable.SwipeLayout_leftEdgeSwipeOffset, 0);
mEdgeSwipesOffset[DragEdge.Right.ordinal()] = a.getDimension(R.styleable.SwipeLayout_rightEdgeSwipeOffset, 0);
mEdgeSwipesOffset[DragEdge.Top.ordinal()] = a.getDimension(R.styleable.SwipeLayout_topEdgeSwipeOffset, 0);
mEdgeSwipesOffset[DragEdge.Bottom.ordinal()] = a.getDimension(R.styleable.SwipeLayout_bottomEdgeSwipeOffset, 0);
setClickToClose(a.getBoolean(R.styleable.SwipeLayout_clickToClose, mClickToClose));

if ((dragEdgeChoices & DRAG_LEFT) == DRAG_LEFT) {
mDragEdges.put(DragEdge.Left, null);
}
if ((dragEdgeChoices & DRAG_TOP) == DRAG_TOP) {
mDragEdges.put(DragEdge.Top, null);
}
if ((dragEdgeChoices & DRAG_RIGHT) == DRAG_RIGHT) {
mDragEdges.put(DragEdge.Right, null);
}
if ((dragEdgeChoices & DRAG_BOTTOM) == DRAG_BOTTOM) {
mDragEdges.put(DragEdge.Bottom, null);
}
int ordinal = a.getInt(R.styleable.SwipeLayout_show_mode, ShowMode.PullOut.ordinal());
mShowMode = ShowMode.values()[ordinal];
a.recycle();

}

先获取属性里DragEdge的int值，如果没有就使用默认的 DragEdge.Right.ordinal()的int值，他的int值表示该枚举类在构造器中的position,然后再通过

mDragEdge = DragEdge.values()[ordinal];来获得真正的枚举值。(ShowMode的参数也是同样的方法获得)

1.首先来分析view的初始化过程

如果是xml中的view，在加载布局的时候会调用addView方法，在这个方法中如果view有设置Gravity属性，会将该view添加到mDragEdges的map中，并设置相应的方向的key：

@Override
public void addView(View child, int index, ViewGroup.LayoutParams params) {
if (child == null) return;
int gravity = Gravity.NO_GRAVITY;
try {
gravity = (Integer) params.getClass().getField("gravity").get(params);
} catch (Exception e) {
e.printStackTrace();
}

if (gravity > 0) {
//兼容LTR和RTL
gravity = GravityCompat.getAbsoluteGravity(gravity, ViewCompat.getLayoutDirection(this));
//根据Gravity的值匹配对应的DragEdgekey值，并将view以value值放入到map中
if ((gravity & Gravity.LEFT) == Gravity.LEFT) {
mDragEdges.put(DragEdge.Left, child);
}
if ((gravity & Gravity.RIGHT) == Gravity.RIGHT) {
mDragEdges.put(DragEdge.Right, child);
}
if ((gravity & Gravity.TOP) == Gravity.TOP) {
mDragEdges.put(DragEdge.Top, child);
}
if ((gravity & Gravity.BOTTOM) == Gravity.BOTTOM) {
mDragEdges.put(DragEdge.Bottom, child);
}
} else {
//如果gravity值小于0，就取寻找map中是否只有key没有value的键值，有就把当前的view和没有值的键组合在一起
for (Map.Entry<DragEdge, View> entry : mDragEdges.entrySet()) {
if (entry.getValue() == null) {
//means used the drag_edge attr, the no gravity child should be use set
mDragEdges.put(entry.getKey(), child);
break;
}
}
}
if (child.getParent() == this) {
return;
}
super.addView(child, index, params);
}

然后就是view的绘制，接着手动布局之前加入到mDragEdges中的隐藏在底部的view：

@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
updateBottomViews();

if (mOnLayoutListeners != null) for (int i = 0; i < mOnLayoutListeners.size(); i++) {
mOnLayoutListeners.get(i).onLayout(this);
}
}

在updateBottomViews方法中通过getCurrentBottomView方法获得当前隐藏在底部的view，由于默认的mCurrentDragEdge设置是DragEdge.Right，所以初始化阶段，currentBottomView默认就是mDragEdges中设置了right标记的view，并计算得出可以拖动的最大偏移量mDragDistance：

// 布局隐藏在下面的view
private void updateBottomViews() {
//获得当前底部的view，并计算可以拖动的距离
View currentBottomView = getCurrentBottomView();
if (currentBottomView != null) {
if (mCurrentDragEdge == DragEdge.Left || mCurrentDragEdge == DragEdge.Right) {
mDragDistance = currentBottomView.getMeasuredWidth() - dp2px(getCurrentOffset());
} else {
mDragDistance = currentBottomView.getMeasuredHeight() - dp2px(getCurrentOffset());
}
}
//布局两种情况下的view
if (mShowMode == ShowMode.PullOut) {
layoutPullOut();
} else if (mShowMode == ShowMode.LayDown) {
layoutLayDown();
}
safeBottomView();
}

并且只会针对该view（在PullOut和LayDown）的情况下进行layout：

void layoutPullOut() {
Rect rect = computeSurfaceLayoutArea(false);
View surfaceView = getSurfaceView();
//布局显示的view
if (surfaceView != null) {
surfaceView.layout(rect.left, rect.top, rect.right, rect.bottom);
bringChildToFront(surfaceView);
}
//布局隐藏在下面的view
rect = computeBottomLayoutAreaViaSurface(ShowMode.PullOut, rect);
View currentBottomView = getCurrentBottomView();
if (currentBottomView != null) {
currentBottomView.layout(rect.left, rect.top, rect.right, rect.bottom);
}
}

void layoutLayDown() {
Rect rect = computeSurfaceLayoutArea(false);
View surfaceView = getSurfaceView();
if (surfaceView != null) {
surfaceView.layout(rect.left, rect.top, rect.right, rect.bottom);
bringChildToFront(surfaceView);
}
rect = computeBottomLayoutAreaViaSurface(ShowMode.LayDown, rect);
View currentBottomView = getCurrentBottomView();
if (currentBottomView != null) {
currentBottomView.layout(rect.left, rect.top, rect.right, rect.bottom);
}
}

/**
* a helper function to compute the Rect area that surface will hold in.
* 计算显示在前面的view的layout位置
*
* @param open open status or close status.
*/
private Rect computeSurfaceLayoutArea(boolean open) {
int l = getPaddingLeft(), t = getPaddingTop();
if (open) {
if (mCurrentDragEdge == DragEdge.Left)
l = getPaddingLeft() + mDragDistance;
else if (mCurrentDragEdge == DragEdge.Right)
l = getPaddingLeft() - mDragDistance;
else if (mCurrentDragEdge == DragEdge.Top)
t = getPaddingTop() + mDragDistance;
else t = getPaddingTop() - mDragDistance;
}
//        return new Rect(l, t, l + getMeasuredWidth(), t + getMeasuredHeight());
return new Rect(l, t, getMeasuredWidth() - l, getMeasuredHeight() - t);
}

/**
* 通过计算获得当前隐藏的view的布局区域
*
* @param mode
* @param surfaceArea
* @return
*/
private Rect computeBottomLayoutAreaViaSurface(ShowMode mode, Rect surfaceArea) {
Rect rect = surfaceArea;
View bottomView = getCurrentBottomView();

int bl = rect.left, bt = rect.top, br = rect.right, bb = rect.bottom;
if (mode == ShowMode.PullOut) {
if (mCurrentDragEdge == DragEdge.Left)
bl = rect.left - mDragDistance;
else if (mCurrentDragEdge == DragEdge.Right)
bl = rect.right;
else if (mCurrentDragEdge == DragEdge.Top)
bt = rect.top - mDragDistance;
else bt = rect.bottom;

if (mCurrentDragEdge == DragEdge.Left || mCurrentDragEdge == DragEdge.Right) {
bb = rect.bottom;
br = bl + (bottomView == null ? 0 : bottomView.getMeasuredWidth());
} else {
bb = bt + (bottomView == null ? 0 : bottomView.getMeasuredHeight());
br = rect.right;
}
} else if (mode == ShowMode.LayDown) {
if (mCurrentDragEdge == DragEdge.Left)
br = bl + mDragDistance;
else if (mCurrentDragEdge == DragEdge.Right)
bl = br - mDragDistance;
else if (mCurrentDragEdge == DragEdge.Top)
bb = bt + mDragDistance;
else bt = bb - mDragDistance;

}
return new Rect(bl, bt, br, bb);

}

/**
* prevent bottom view get any touch event. Especially in LayDown mode.
* 把不需要的view设置为INVISIBLE，以避免触摸事件冲突
*/
private void safeBottomView() {
Status status = getOpenStatus();
List<View> bottoms = getBottomViews();

if (status == Status.Close) {
for (View bottom : bottoms) {
if (bottom != null && bottom.getVisibility() != INVISIBLE) {
bottom.setVisibility(INVISIBLE);
}
}
} else {
View currentBottomView = getCurrentBottomView();
if (currentBottomView != null && currentBottomView.getVisibility() != VISIBLE) {
currentBottomView.setVisibility(VISIBLE);
}
}
}

2.接下来分析拖动的过程：

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
if (!isSwipeEnabled()) {
return false;
}
if (mClickToClose && getOpenStatus() == Status.Open && isTouchOnSurface(ev)) {
return true;
}
for (SwipeDenier denier : mSwipeDeniers) {
if (denier != null && denier.shouldDenySwipe(ev)) {
return false;
}
}

switch (ev.getAction()) {
case MotionEvent.ACTION_DOWN:
mDragHelper.processTouchEvent(ev);
mIsBeingDragged = false;
sX = ev.getRawX();
sY = ev.getRawY();
//if the swipe is in middle state(scrolling), should intercept the touch
if (getOpenStatus() == Status.Middle) {
mIsBeingDragged = true;
}
break;
case MotionEvent.ACTION_MOVE:
boolean beforeCheck = mIsBeingDragged;
checkCanDrag(ev);
if (mIsBeingDragged) {
ViewParent parent = getParent();
if (parent != null) {
parent.requestDisallowInterceptTouchEvent(true);
}
}
if (!beforeCheck && mIsBeingDragged) {
//let children has one chance to catch the touch, and request the swipe not intercept
//useful when swipeLayout wrap a swipeLayout or other gestural layout
return false;
}
break;

case MotionEvent.ACTION_CANCEL:
case MotionEvent.ACTION_UP:
mIsBeingDragged = false;
mDragHelper.processTouchEvent(ev);
break;
default://handle other action, such as ACTION_POINTER_DOWN/UP
mDragHelper.processTouchEvent(ev);
}
return mIsBeingDragged;
}

触摸拦截方法中重要的是ACTION_DOWN和ACTION_MOVE，在ACTION_DOWN需要先调用mDragHelper.processTouchEvent(ev);方法在ViewDragHelp中记录点击的位置，其实一般是用mDragHelper.shouldInterceptTouchEvent(ev)方法。在ACTION_MOVE方法中通过局部变量来记录mIsBeingDragged的状态，是为了刚开始拖动的时候，让子的

swipeLayout（就是swipeLayout嵌套swipeLayout的情况）布局可以有机会捕捉到触摸事件，并通过checkCanDrag(ev)：

/**
* 检验当前的拖动动作能否触发拖动
* 如果可以拖动就通过setCurrentDragEdge(dragEdge)设置当前的
* dragEdge
*
* @param ev
*/
private void checkCanDrag(MotionEvent ev) {
if (mIsBeingDragged) return;
if (getOpenStatus() == Status.Middle) {
mIsBeingDragged = true;
return;
}
Status status = getOpenStatus();
float distanceX = ev.getRawX() - sX;
float distanceY = ev.getRawY() - sY;
float angle = Math.abs(distanceY / distanceX);
angle = (float) Math.toDegrees(Math.atan(angle));
if (getOpenStatus() == Status.Close) {
DragEdge dragEdge;
if (angle < 45) {
if (distanceX > 0 && isLeftSwipeEnabled()) {
dragEdge = DragEdge.Left;
} else if (distanceX < 0 && isRightSwipeEnabled()) {
dragEdge = DragEdge.Right;
} else return;

} else {
if (distanceY > 0 && isTopSwipeEnabled()) {
dragEdge = DragEdge.Top;
} else if (distanceY < 0 && isBottomSwipeEnabled()) {
dragEdge = DragEdge.Bottom;
} else return;
}
setCurrentDragEdge(dragEdge);
}

boolean doNothing = false;
if (mCurrentDragEdge == DragEdge.Right) {
boolean suitable = (status == Status.Open && distanceX > mTouchSlop)
|| (status == Status.Close && distanceX < -mTouchSlop);
suitable = suitable || (status == Status.Middle);

if (angle > 30 || !suitable) {
doNothing = true;
}
}

if (mCurrentDragEdge == DragEdge.Left) {
boolean suitable = (status == Status.Open && distanceX < -mTouchSlop)
|| (status == Status.Close && distanceX > mTouchSlop);
suitable = suitable || status == Status.Middle;

if (angle > 30 || !suitable) {
doNothing = true;
}
}

if (mCurrentDragEdge == DragEdge.Top) {
boolean suitable = (status == Status.Open && distanceY < -mTouchSlop)
|| (status == Status.Close && distanceY > mTouchSlop);
suitable = suitable || status == Status.Middle;

if (angle < 60 || !suitable) {
doNothing = true;
}
}

if (mCurrentDragEdge == DragEdge.Bottom) {
boolean suitable = (status == Status.Open && distanceY > mTouchSlop)
|| (status == Status.Close && distanceY < -mTouchSlop);
suitable = suitable || status == Status.Middle;

if (angle < 60 || !suitable) {
doNothing = true;
}
}
mIsBeingDragged = !doNothing;
}

来判断底部是否有隐藏的view，是否有可以拖动的行为，如果可以，就通过如下代码来请求父布局不打断触摸事件，这样以后的移动事件都将由子swipeLayout布局的onTouchEvent方法来处理（如果不是为了这个用途，就不用自己记录mIsBeingDragged的标记，因为在ViewDragHelper中可以通过getViewDragState()来获得拖动的状态）：

if (mIsBeingDragged) {
ViewParent parent = getParent();
if (parent != null) {
parent.requestDisallowInterceptTouchEvent(true);
}
}

然后真正处理事件是放在onTouchEvent方法中进行的：

@Override
public boolean onTouchEvent(MotionEvent event) {
if (!isSwipeEnabled()) return super.onTouchEvent(event);

int action = event.getActionMasked();
gestureDetector.onTouchEvent(event);
switch (action) {
case MotionEvent.ACTION_DOWN:
mDragHelper.processTouchEvent(event);
sX = event.getRawX();
sY = event.getRawY();

case MotionEvent.ACTION_MOVE: {
//the drag state and the direction are already judged at onInterceptTouchEvent
checkCanDrag(event);
if (mIsBeingDragged) {
getParent().requestDisallowInterceptTouchEvent(true);
mDragHelper.processTouchEvent(event);
}
break;
}
case MotionEvent.ACTION_UP:
case MotionEvent.ACTION_CANCEL:
mIsBeingDragged = false;
mDragHelper.processTouchEvent(event);
break;

default://handle other action, such as ACTION_POINTER_DOWN/UP
mDragHelper.processTouchEvent(event);
}

return super.onTouchEvent(event) || mIsBeingDragged || action == MotionEvent.ACTION_DOWN;
}

重点就是调用了mDragHelper.processTouchEvent(event);方法，这个方法会在ViewDragHelper中帮我们处理很多东西，并通过回调类mDragHelperCallback的各种方法来将需要的参数回调给我们。

接下来看mDragHelperCallback对象：

private ViewDragHelper.Callback mDragHelperCallback = new ViewDragHelper.Callback() {

@Override
public int clampViewPositionHorizontal(View child, int left, int dx) {
if (child == getSurfaceView()) {
//在拖动显示在前面的view的情况
switch (mCurrentDragEdge) {
//上下拖动的时候，设置左右不滑动
case Top:
case Bottom:
return getPaddingLeft();
//隐藏在左边，可以向右拖动，
case Left:
//向右再往回拉的时候最多只能拉到PaddingLeft的位置
if (left < getPaddingLeft()) return getPaddingLeft();
//向右可以拉倒PaddingLeft加上mDragDistance的位置
if (left > getPaddingLeft() + mDragDistance)
return getPaddingLeft() + mDragDistance;
break;
case Right:
if (left > getPaddingLeft()) return getPaddingLeft();
if (left < getPaddingLeft() - mDragDistance)
return getPaddingLeft() - mDragDistance;
break;
}
} else if (getCurrentBottomView() == child) {
//在拖动显示隐藏的view的情况
switch (mCurrentDragEdge) {
case Top:
case Bottom:
return getPaddingLeft();
case Left:
//左边隐藏的view在向右边拖动的时候最多只能拖到PaddingLeft位置
if (mShowMode == ShowMode.PullOut) {
if (left > getPaddingLeft()) return getPaddingLeft();
}
break;
case Right:
if (mShowMode == ShowMode.PullOut) {
if (left < getMeasuredWidth() - mDragDistance) {
return getMeasuredWidth() - mDragDistance;
}
}
break;
}
}
return left;
}

@Override
public int clampViewPositionVertical(View child, int top, int dy) {
if (child == getSurfaceView()) {
switch (mCurrentDragEdge) {
case Left:
case Right:
return getPaddingTop();
case Top:
if (top < getPaddingTop()) return getPaddingTop();
if (top > getPaddingTop() + mDragDistance)
return getPaddingTop() + mDragDistance;
break;
case Bottom:
if (top < getPaddingTop() - mDragDistance) {
return getPaddingTop() - mDragDistance;
}
if (top > getPaddingTop()) {
return getPaddingTop();
}
}
} else {
View surfaceView = getSurfaceView();
int surfaceViewTop = surfaceView == null ? 0 : surfaceView.getTop();
switch (mCurrentDragEdge) {
case Left:
case Right:
return getPaddingTop();
case Top:
if (mShowMode == ShowMode.PullOut) {
if (top > getPaddingTop()) return getPaddingTop();
} else {
if (surfaceViewTop + dy < getPaddingTop())
return getPaddingTop();
if (surfaceViewTop + dy > getPaddingTop() + mDragDistance)
return getPaddingTop() + mDragDistance;
}
break;
case Bottom:
if (mShowMode == ShowMode.PullOut) {
if (top < getMeasuredHeight() - mDragDistance)
return getMeasuredHeight() - mDragDistance;
} else {
if (surfaceViewTop + dy >= getPaddingTop())
return getPaddingTop();
if (surfaceViewTop + dy <= getPaddingTop() - mDragDistance)
return getPaddingTop() - mDragDistance;
}
}
}
return top;
}

@Override
public boolean tryCaptureView(View child, int pointerId) {
// 如果显示是前面的view或者是集合中隐藏的view
boolean result = child == getSurfaceView() || getBottomViews().contains(child);
if (result) {
isCloseBeforeDrag = getOpenStatus() == Status.Close;
}
return result;
}

@Override
public int getViewHorizontalDragRange(View child) {
return mDragDistance;
}

@Override
public int getViewVerticalDragRange(View child) {
return mDragDistance;
}

boolean isCloseBeforeDrag = true;

@Override
public void onViewReleased(View releasedChild, float xvel, float yvel) {
super.onViewReleased(releasedChild, xvel, yvel);
processHandRelease(xvel, yvel, isCloseBeforeDrag);
for (SwipeListener l : mSwipeListeners) {
l.onHandRelease(SwipeLayout.this, xvel, yvel);
}
invalidate();
}

@Override
public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
View surfaceView = getSurfaceView();
if (surfaceView == null) return;
View currentBottomView = getCurrentBottomView();
int evLeft = surfaceView.getLeft(), evRight = surfaceView.getRight(), evTop = surfaceView.getTop(), evBottom = surfaceView.getBottom();
//如果移动的是上面的view
if (changedView == surfaceView) {
//如果是PullOut模式且存在隐藏的view
if (mShowMode == ShowMode.PullOut && currentBottomView != null) {
//设置隐藏的view跟随移动
if (mCurrentDragEdge == DragEdge.Left || mCurrentDragEdge == DragEdge.Right) {
currentBottomView.offsetLeftAndRight(dx);
} else {
currentBottomView.offsetTopAndBottom(dy);
}
}
} else if (getBottomViews().contains(changedView)) {
//如果移动的是隐藏的view
if (mShowMode == ShowMode.PullOut) {
//设置PullOut模式下的上面的view跟随移动
surfaceView.offsetLeftAndRight(dx);
surfaceView.offsetTopAndBottom(dy);
} else {
//需要控制底部的view始终保持不动
Rect rect = computeBottomLayDown(mCurrentDragEdge);
if (currentBottomView != null) {
currentBottomView.layout(rect.left, rect.top, rect.right, rect.bottom);
}
//而surfaceView则需要向拖动的方向移动
surfaceView.offsetLeftAndRight(dx);
surfaceView.offsetTopAndBottom(dy);
//
//                    int newLeft = surfaceView.getLeft() + dx, newTop = surfaceView.getTop() + dy;
//
//                    if (mCurrentDragEdge == DragEdge.Left && newLeft < getPaddingLeft())
//                        newLeft = getPaddingLeft();
//                    else if (mCurrentDragEdge == DragEdge.Right && newLeft > getPaddingLeft())
//                        newLeft = getPaddingLeft();
//                    else if (mCurrentDragEdge == DragEdge.Top && newTop < getPaddingTop())
//                        newTop = getPaddingTop();
//                    else if (mCurrentDragEdge == DragEdge.Bottom && newTop > getPaddingTop())
//                        newTop = getPaddingTop();
//
//                    surfaceView.layout(newLeft, newTop, newLeft + getMeasuredWidth(), newTop + getMeasuredHeight());
}
}

dispatchRevealEvent(evLeft, evTop, evRight, evBottom);

dispatchSwipeEvent(evLeft, evTop, dx, dy);

invalidate();
}
};

tryCaptureView：

由于拖动的可能是显示的view，也可能是子view，所以只要是这两种view，都会返回true.

clampViewPositionHorizontal(View child, int left, int dx)：

参数中view就是当前拖动的view，返回的left就是当前view的最左边将要移动到的位置，所以在该方法中是为了防止view被拖出边界即可。

clampViewPositionVertical(View child, int top, int dy):

如上

onViewPositionChanged(View changedView, int left, int top, int dx, int dy)：

如果在拖动view的时候会引起另一些view的相应移动，就要在此方法中作相应的操作，如果拖动的view是surfaceView，那么当前隐藏在下面的view就要通过

currentBottomView.offsetLeftAndRight(dx)

方法来设置相应的跟随移动；那如果拖动的view是bottomView:在PullOut模式下还是通过

//设置PullOut模式下的上面的view跟随移动
surfaceView.offsetLeftAndRight(dx);
surfaceView.offsetTopAndBottom(dy);

来移动，但假如是LayDown模式，假设在左边现在有一个隐藏的view，这时候通过拖动bottomView使其恢复到原来的位置，但是拖动的时候会发现bottomView往左边移动了，而实际需要的效果是bottomView不动，surfaceView向左边移动。所以需要通过

//需要控制底部的view始终保持不动
Rect rect = computeBottomLayDown(mCurrentDragEdge);
if (currentBottomView != null) {
currentBottomView.layout(rect.left, rect.top, rect.right, rect.bottom);
}

设置底部的view的位置不变，而surfaceView则需要作相应的移动：

//而surfaceView则需要向拖动的方向移动
surfaceView.offsetLeftAndRight(dx);
surfaceView.offsetTopAndBottom(dy);

然后在拖动的过程中会调用这三个方法：

dispatchRevealEvent(evLeft, evTop, evRight, evBottom);

dispatchSwipeEvent(evLeft, evTop, dx, dy);

invalidate();

onViewReleased(View releasedChild, float xvel, float yvel)：

如果在拖动的过程中，手指移开了，拖动的view会自动回到对应的位置，这是通过processHandRelease方法来执行的，他里面通过判断手指拖动的时候的速度值xvel和获取的最小速度150.0作比较，如果速度是在-150和150两边的速度，会相应的调用open()或者close()方法，如果速度是在这两个数值中间的，就通过移动的距离来判断应该open()还是close()：

/**
* Process the surface release event.
*
* @param xvel                 xVelocity
* @param yvel                 yVelocity
* @param isCloseBeforeDragged the open state before drag
*/
protected void processHandRelease(float xvel, float yvel, boolean isCloseBeforeDragged) {
//获得最小速度,150.0
float minVelocity = mDragHelper.getMinVelocity();
Log.i("llj","minVelocity:"+minVelocity+"xvel:"+xvel);
View surfaceView = getSurfaceView();
DragEdge currentDragEdge = mCurrentDragEdge;
if (currentDragEdge == null || surfaceView == null) {
return;
}
//如果在拖动前是关着的，设置临界值是0.25，否则是0.75
float willOpenPercent = (isCloseBeforeDragged ? .25f : .75f);
if (currentDragEdge == DragEdge.Left) {
//如果速度比150大
if (xvel > minVelocity) open();
//如果速度比-150小
else if (xvel < -minVelocity) close();
else {
//速度在-150到150之间的，通过移动的距离判断是否open()或者close()
float openPercent = 1f * getSurfaceView().getLeft() / mDragDistance;
if (openPercent > willOpenPercent) open();
else close();
}
} else if (currentDragEdge == DragEdge.Right) {
if (xvel > minVelocity) close();
else if (xvel < -minVelocity) open();
else {
float openPercent = 1f * (-getSurfaceView().getLeft()) / mDragDistance;
if (openPercent > willOpenPercent) open();
else close();
}
} else if (currentDragEdge == DragEdge.Top) {
if (yvel > minVelocity) open();
else if (yvel < -minVelocity) close();
else {
float openPercent = 1f * getSurfaceView().getTop() / mDragDistance;
if (openPercent > willOpenPercent) open();
else close();
}
} else if (currentDragEdge == DragEdge.Bottom) {
if (yvel > minVelocity) close();
else if (yvel < -minVelocity) open();
else {
float openPercent = 1f * (-getSurfaceView().getTop()) / mDragDistance;
if (openPercent > willOpenPercent) open();
else close();
}
}
}

open()方法有两种移动的方式，一种是平滑的，一种是瞬移的，平滑的就先通过computeSurfaceLayoutArea方法获取打开后surfaceView应该处于的位置，然后通过smoothSlideViewTo滑到相应的位置，不用管bottomView，因为他会在onViewPositionChanged中作相应的跟随移动；而如果是非平滑的分别通过computeSurfaceLayoutArea和computeBottomLayoutAreaViaSurface方法获取surfaceView和bottomView的最终位置，并通过layout来设置位置，invalidate方法来执行重绘:

public void open(boolean smooth, boolean notify) {
View surface = getSurfaceView(), bottom = getCurrentBottomView();
if (surface == null) {
return;
}
int dx, dy;
//获取surfaceView的相应的位置
Rect rect = computeSurfaceLayoutArea(true);
//如果是平滑移动
if (smooth) {
mDragHelper.smoothSlideViewTo(surface, rect.left, rect.top);
} else {
dx = rect.left - surface.getLeft();
dy = rect.top - surface.getTop();
surface.layout(rect.left, rect.top, rect.right, rect.bottom);
//如果是PullOut模式，也需要设置bottomView的重新layout
//获取的位置应该是比rect.left往左边偏移mDragDistance的距离
if (getShowMode() == ShowMode.PullOut) {
Rect bRect = computeBottomLayoutAreaViaSurface(ShowMode.PullOut, rect);
if (bottom != null) {
bottom.layout(bRect.left, bRect.top, bRect.right, bRect.bottom);
}
}
if (notify) {
dispatchRevealEvent(rect.left, rect.top, rect.right, rect.bottom);
dispatchSwipeEvent(rect.left, rect.top, dx, dy);
} else {
safeBottomView();
}
}
invalidate();
}

close()方法的过程和上面的open()类似：

/**
* close surface
*
* @param smooth smoothly or not.
* @param notify if notify all the listeners.
*/
public void close(boolean smooth, boolean notify) {
View surface = getSurfaceView();
if (surface == null) {
return;
}
int dx, dy;
if (smooth)
//如果是平滑移动，调用如下方法，然后bottomView会在onViewPositionChanged滑到对应的位置
mDragHelper.smoothSlideViewTo(getSurfaceView(), getPaddingLeft(), getPaddingTop());
else {
//如果是瞬回到初始化位置，直接通过layout设置，
// 不用管底部隐藏的view，因为在重新拖动的时候底部的view会重新layout位置
Rect rect = computeSurfaceLayoutArea(false);
dx = rect.left - surface.getLeft();
dy = rect.top - surface.getTop();
surface.layout(rect.left, rect.top, rect.right, rect.bottom);
if (notify) {
dispatchRevealEvent(rect.left, rect.top, rect.right, rect.bottom);
dispatchSwipeEvent(rect.left, rect.top, dx, dy);
} else {
safeBottomView();
}
}
invalidate();
}

3.接下来分析两个事件的分发过程：

dispatchRevealEvent(evLeft, evTop, evRight, evBottom)：

首先通过getRelativePosition(child)来计算出拖动过程中指定的view应该出现的位置，因为拖动的view可以是一个layout，而指定的view可能只是其中的子view，所以通过此方法得出子view在拖动过程中的对应位置，然后通过isViewShowing方法来判断当前子view是否被用户所看见。假设是left得到隐藏布局，就是通过子view右边的边界和paddingLeft这个临界点来作对比（if (childRight >= getPaddingLeft() && childLeft
< getPaddingLeft()) return true;),如果是可见的就通过计算得出参数distance(移动的距离)和fraction(移动的距离占子view宽度的比重)的值，然后通过(l.onReveal(child, mCurrentDragEdge, Math.abs(fraction), distance);)方法回调给监听器；如果fraction比重的绝对值为1，说明该子view已经完全显示出来，接着就加到mShowEntirely的一个map中：

//分发揭示事件
protected void dispatchRevealEvent(final int surfaceLeft, final int surfaceTop, final int surfaceRight, final int surfaceBottom) {
if (mRevealListeners.isEmpty()) return;
for (Map.Entry<View, ArrayList<OnRevealListener>> entry : mRevealListeners.entrySet()) {
View child = entry.getKey();
//通过计算得出此时该view应该出现的位置
Rect rect = getRelativePosition(child);
if (isViewShowing(child, rect, mCurrentDragEdge, surfaceLeft, surfaceTop, surfaceRight, surfaceBottom)) {
//如果指定的view显示在外面
mShowEntirely.put(child, false);
int distance = 0;
float fraction = 0f;
if (getShowMode() == ShowMode.LayDown) {
switch (mCurrentDragEdge) {
case Left:
//                            Log.i("llj", "rect.left:" + rect.left + "surfaceLeft：" + surfaceLeft);
distance = rect.left - surfaceLeft;
fraction = distance / (float) child.getWidth();
break;
case Right:
distance = rect.right - surfaceRight;
fraction = distance / (float) child.getWidth();
break;
case Top:
distance = rect.top - surfaceTop;
fraction = distance / (float) child.getHeight();
break;
case Bottom:
distance = rect.bottom - surfaceBottom;
fraction = distance / (float) child.getHeight();
break;
}
} else if (getShowMode() == ShowMode.PullOut) {
switch (mCurrentDragEdge) {
case Left:
//计算向右移动了多少距离
distance = rect.right - getPaddingLeft();
//计算向右移动的距离占了指定view的宽度的比重
fraction = distance / (float) child.getWidth();
break;
case Right:
distance = rect.left - getWidth();
fraction = distance / (float) child.getWidth();
break;
case Top:
distance = rect.bottom - getPaddingTop();
fraction = distance / (float) child.getHeight();
break;
case Bottom:
distance = rect.top - getHeight();
fraction = distance / (float) child.getHeight();
break;
}
}
//遍历分发监听器，如果已经完全打开就把view添加到map中
for (OnRevealListener l : entry.getValue()) {
l.onReveal(child, mCurrentDragEdge, Math.abs(fraction), distance);
if (Math.abs(fraction) == 1) {
mShowEntirely.put(child, true);
}
}
}
//如果已经完全打开就回调监听器
if (isViewTotallyFirstShowed(child, rect, mCurrentDragEdge, surfaceLeft, surfaceTop, surfaceRight, surfaceBottom)) {
mShowEntirely.put(child, true);
for (OnRevealListener l : entry.getValue()) {
if (mCurrentDragEdge == DragEdge.Left || mCurrentDragEdge == DragEdge.Right)
l.onReveal(child, mCurrentDragEdge, 1, child.getWidth());
else
l.onReveal(child, mCurrentDragEdge, 1, child.getHeight());
}
}

}
}

dispatchSwipeEvent(evLeft, evTop, dx, dy)：

首先通过dx和dy来判断当前的拖动的view是正在打开还是正在关闭的状态：

//分发SwipeListener监听器,判断正在打开还是正在关闭
protected void dispatchSwipeEvent(int surfaceLeft, int surfaceTop, int dx, int dy) {
DragEdge edge = getDragEdge();
boolean open = true;
if (edge == DragEdge.Left) {
if (dx < 0) open = false;
} else if (edge == DragEdge.Right) {
if (dx > 0) open = false;
} else if (edge == DragEdge.Top) {
if (dy < 0) open = false;
} else if (edge == DragEdge.Bottom) {
if (dy > 0) open = false;
}
dispatchSwipeEvent(surfaceLeft, surfaceTop, open);
}

然后在刚开始打开，打开的过程中，完全打开,刚开始关闭，关闭的过程，完全关闭的几个情况下都做了相应的回调：

//分发SwipeListener监听器
protected void dispatchSwipeEvent(int surfaceLeft, int surfaceTop, boolean open) {
//        Log.i("llj", "surfaceLeft - getPaddingLeft():" + (surfaceLeft - getPaddingLeft()));
safeBottomView();
Status status = getOpenStatus();

if (!mSwipeListeners.isEmpty()) {
mEventCounter++;
for (SwipeListener l : mSwipeListeners) {
//将要打开或者关闭，只回调一次
if (mEventCounter == 1) {
if (open) {
l.onStartOpen(this);
} else {
l.onStartClose(this);
}
}
//打开或者关闭的中间过程
l.onUpdate(SwipeLayout.this, surfaceLeft - getPaddingLeft(), surfaceTop - getPaddingTop());
}
//完全关闭
if (status == Status.Close) {
for (SwipeListener l : mSwipeListeners) {
l.onClose(SwipeLayout.this);
}
mEventCounter = 0;
}
// 完全打开
if (status == Status.Open) {
View currentBottomView = getCurrentBottomView();
if (currentBottomView != null) {
currentBottomView.setEnabled(true);
}
for (SwipeListener l : mSwipeListeners) {
l.onOpen(SwipeLayout.this);
}
mEventCounter = 0;
}
}
}

我们简单的通过拆分成三块来分析了该类库核心类的作用。