本博客原地址:http://www.jianshu.com/p/92b884d8471c
（1）引言
SwipeBackActivity 顾名思义，滑动返回的activity。
swipeBackActivity示意图
这里参考 ikew0ng/ SwipeBackLayout 的github地址。
自己平时学习也有一个习惯，就是将别人的项目，一点一点copy过来，并在原来的代码上做出一些修改。通过这种方式来学习别人的开源代码。所以这里有了我的一个项目地址： 我的 SwipeBackActivity github地址
写这篇文章是因为在接下来的博客中将会利用SwipeBackActivity来搭建整个activity的体系。让所有的activity都能够实现滑动返回。这年头屏幕这么大，又取消了实体键。返回键在左上角真的是难得按。
（2）源码分析
2.1 使用swipebackActivitity ，如图，只需要继承SwipeBackActivity
demoActivity继承自SwipeBackActivity来使用此功能
并且注意在manifest文件中定义theme，添加如下属性：
使用SwipeBackActivity 的activity添加theme属性
2.2 来看看swipeBackActivity是怎么实现的:
package nsu.edu.com.library;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
/**
* all the subClass extends from this class to use swipe-back function
*/
public class SwipeBackActivity extends AppCompatActivity implements SwipeBackActivityBase {
private SwipeBackActivityHelper mHelper;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mHelper = new SwipeBackActivityHelper(this);
mHelper.onActivityCreate();
}
@Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
mHelper.onPostCreate();
}
@Override
public View findViewById(int id) {
View v = super.findViewById(id);
if (v == null && mHelper != null)
return mHelper.findViewById(id);
return v;
}
@Override
public SwipeBackLayout getSwipeBackLayout() {
return mHelper.getSwipeBackLayout();
}
@Override
public void setSwipeBackEnable(boolean enable) {
getSwipeBackLayout().setEnableGesture(enable);
}
@Override
public void scrollToFinishActivity() {
Utils.convertActivityToTranslucent(this);
getSwipeBackLayout().scrollToFinishActivity();
}
}
可以看到只需要对SwipeBackActivityBase 进行实现，其实主要的操作是由SwipeBackActivityHelper 的对象完成的。它主要完成了SwipeBackActivity在onCreate，onPostCreate，以及findViewById，都将操作传递给了SwipeBackActivityHelper 的对象。那么接下来看看它是怎么实现的.
2.3 来看看SwipeBackActivityHelper 是怎么实现的。
package nsu.edu.com.library;
import android.app.Activity;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.view.LayoutInflater;
import android.view.View;
/**
*
*/
public class SwipeBackActivityHelper {
private Activity mActivity;
private SwipeBackLayout mSwipeBackLayout;
public SwipeBackActivityHelper(Activity activity) {
mActivity = activity;
}
@SuppressWarnings("deprecation")
public void onActivityCreate() {
mActivity.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
mActivity.getWindow().getDecorView().setBackgroundDrawable(null);
mSwipeBackLayout = (SwipeBackLayout) LayoutInflater.from(mActivity).inflate(
R.layout.swipeback_layout, null);
mSwipeBackLayout.addSwipeListener(new SwipeBackLayout.SwipeListener() {
@Override
public void onScrollStateChange(int state, float scrollPercent) {
}
@Override
public void onEdgeTouch(int edgeFlag) {
Utils.convertActivityToTranslucent(mActivity);
}
@Override
public void onScrollOverThreshold() {
}
});
}
public void onPostCreate() {
mSwipeBackLayout.attachToActivity(mActivity);
}
public View findViewById(int id) {
if (mSwipeBackLayout != null) {
return mSwipeBackLayout.findViewById(id);
}
return null;
}
public SwipeBackLayout getSwipeBackLayout() {
return mSwipeBackLayout;
}
}
其中进行的操作： 在activity调用onCreate之后会调用这的onActivityCreated,里面主要进行的操作是初始化SwipeBackLayout，并且将window的背景置为透明，然后设置SwipeBackLayout的滑动监听； 在activity的onPostCreate中也会调用这里的onPostCreate，将activity设置给SwipeBackLayout对象的attachToActivity; findViewById方法也是将操作进一步传递给SwipeBackLayout的对象。
2.4 下面就来看看SwipeBackLayout的实现，也是整个项目的重点：
package nsu.edu.com.library;
import android.app.Activity;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.support.v4.view.ViewCompat;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.FrameLayout;
import java.util.ArrayList;
import java.util.List;
public class SwipeBackLayout extends FrameLayout {
/**
* Minimum velocity that will be detected as a fling
*/
private static final int MIN_FLING_VELOCITY = 400; // dips per second
private static final int DEFAULT_SCRIM_COLOR = 0x99000000;
private static final int FULL_ALPHA = 255;
/**
* Edge flag indicating that the left edge should be affected.
*/
public static final int EDGE_LEFT = ViewDragHelper.EDGE_LEFT;
/**
* Edge flag indicating that the right edge should be affected.
*/
public static final int EDGE_RIGHT = ViewDragHelper.EDGE_RIGHT;
/**
* Edge flag indicating that the bottom edge should be affected.
*/
public static final int EDGE_BOTTOM = ViewDragHelper.EDGE_BOTTOM;
/**
* Edge flag set indicating all edges should be affected.
*/
public static final int EDGE_ALL = EDGE_LEFT | EDGE_RIGHT | EDGE_BOTTOM;
/**
* A view is not currently being dragged or animating as a result of a
* fling/snap.
*/
public static final int STATE_IDLE = ViewDragHelper.STATE_IDLE;
/**
* A view is currently being dragged. The position is currently changing as
* a result of user input or simulated user input.
*/
public static final int STATE_DRAGGING = ViewDragHelper.STATE_DRAGGING;
/**
* A view is currently settling into place as a result of a fling or
* predefined non-interactive motion.
*/
public static final int STATE_SETTLING = ViewDragHelper.STATE_SETTLING;
/**
* Default threshold of scroll
*/
private static final float DEFAULT_SCROLL_THRESHOLD = 0.3f;
private static final int OVERSCROLL_DISTANCE = 10;
private static final int[] EDGE_FLAGS = {
EDGE_LEFT, EDGE_RIGHT, EDGE_BOTTOM, EDGE_ALL
};
private int mEdgeFlag;
/**
* Threshold of scroll, we will close the activity, when scrollPercent over
* this value;
*/
private float mScrollThreshold = DEFAULT_SCROLL_THRESHOLD;
private Activity mActivity;
private boolean mEnable = true;
private View mContentView;
private ViewDragHelper mDragHelper;
private float mScrollPercent;
private int mContentLeft;
private int mContentTop;
/**
* The set of listeners to be sent events through.
*/
private List mListeners;
private Drawable mShadowLeft;
private Drawable mShadowRight;
private Drawable mShadowBottom;
private float mScrimOpacity;
private int mScrimColor = DEFAULT_SCRIM_COLOR;
private boolean mInLayout;
private Rect mTmpRect = new Rect();
/**
* Edge being dragged
*/
private int mTrackingEdge;
public SwipeBackLayout(Context context) {
this(context, null);
}
public SwipeBackLayout(Context context, AttributeSet attrs) {
this(context, attrs, R.attr.SwipeBackLayoutStyle);
}
public SwipeBackLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs);
mDragHelper = ViewDragHelper.create(this, new ViewDragCallback());
TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.SwipeBackLayout, defStyle,
R.style.SwipeBackLayout);
int edgeSize = a.getDimensionPixelSize(R.styleable.SwipeBackLayout_edge_size, -1);
if (edgeSize > 0)
setEdgeSize(edgeSize);
int mode = EDGE_FLAGS[a.getInt(R.styleable.SwipeBackLayout_edge_flag, 0)];
setEdgeTrackingEnabled(mode);
int shadowLeft = a.getResourceId(R.styleable.SwipeBackLayout_shadow_left,
R.drawable.shadow_left);
int shadowRight = a.getResourceId(R.styleable.SwipeBackLayout_shadow_right,
R.drawable.shadow_right);
int shadowBottom = a.getResourceId(R.styleable.SwipeBackLayout_shadow_bottom,
R.drawable.shadow_bottom);
setShadow(shadowLeft, EDGE_LEFT);
setShadow(shadowRight, EDGE_RIGHT);
setShadow(shadowBottom, EDGE_BOTTOM);
a.recycle();
final float density = getResources().getDisplayMetrics().density;
final float minVel = MIN_FLING_VELOCITY * density;
mDragHelper.setMinVelocity(minVel);
mDragHelper.setMaxVelocity(minVel * 2f);
}
/**
* Sets the sensitivity of the NavigationLayout.
*
* @param context The application context.
* @param sensitivity value between 0 and 1, the final value for touchSlop =
* ViewConfiguration.getScaledTouchSlop * (1 / s);
*/
public void setSensitivity(Context context, float sensitivity) {
mDragHelper.setSensitivity(context, sensitivity);
}
/**
* Set up contentView which will be moved by user gesture
*
* @param view
*/
private void setContentView(View view) {
mContentView = view;
}
public void setEnableGesture(boolean enable) {
mEnable = enable;
}
/**
* Enable edge tracking for the selected edges of the parent view. The
* callback's
* {@link ViewDragHelper.Callback#onEdgeTouched(int, int)}
* and
* {@link ViewDragHelper.Callback#onEdgeDragStarted(int, int)}
* methods will only be invoked for edges for which edge tracking has been
* enabled.
*
* @param edgeFlags Combination of edge flags describing the edges to watch
* @see #EDGE_LEFT
* @see #EDGE_RIGHT
* @see #EDGE_BOTTOM
*/
public void setEdgeTrackingEnabled(int edgeFlags) {
mEdgeFlag = edgeFlags;
mDragHelper.setEdgeTrackingEnabled(mEdgeFlag);
}
/**
* Set a color to use for the scrim that obscures primary content while a
* drawer is open.
*
* @param color Color to use in 0xAARRGGBB format.
*/
public void setScrimColor(int color) {
mScrimColor = color;
invalidate();
}
/**
* Set the size of an edge. This is the range in pixels along the edges of
* this view that will actively detect edge touches or drags if edge
* tracking is enabled.
*
* @param size The size of an edge in pixels
*/
public void setEdgeSize(int size) {
mDragHelper.setEdgeSize(size);
}
/**
* Register a callback to be invoked when a swipe event is sent to this
* view.
*
* @param listener the swipe listener to attach to this view
* @deprecated use {@link #addSwipeListener} instead
*/
@Deprecated
public void setSwipeListener(SwipeListener listener) {
addSwipeListener(listener);
}
/**
* Add a callback to be invoked when a swipe event is sent to this view.
*
* @param listener the swipe listener to attach to this view
*/
public void addSwipeListener(SwipeListener listener) {
if (mListeners == null) {
mListeners = new ArrayList();
}
mListeners.add(listener);
}
/**
* Removes a listener from the set of listeners
*
* @param listener
*/
public void removeSwipeListener(SwipeListener listener) {
if (mListeners == null) {
return;
}
mListeners.remove(listener);
}
public static interface SwipeListener {
/**
* Invoke when state change
*
* @param state flag to describe scroll state
* @param scrollPercent scroll percent of this view
* @see #STATE_IDLE
* @see #STATE_DRAGGING
* @see #STATE_SETTLING
*/
public void onScrollStateChange(int state, float scrollPercent);
/**
* Invoke when edge touched
*
* @param edgeFlag edge flag describing the edge being touched
* @see #EDGE_LEFT
* @see #EDGE_RIGHT
* @see #EDGE_BOTTOM
*/
public void onEdgeTouch(int edgeFlag);
/**
* Invoke when scroll percent over the threshold for the first time
*/
public void onScrollOverThreshold();
}
/**
* Set scroll threshold, we will close the activity, when scrollPercent over
* this value
*
* @param threshold
*/
public void setScrollThresHold(float threshold) {
if (threshold >= 1.0f || threshold <= 0) {
throw new IllegalArgumentException("Threshold value should be between 0 and 1.0");
}
mScrollThreshold = threshold;
}
/**
* Set a drawable used for edge shadow.
*
* @param shadow Drawable to use
* @param edgeFlag Combination of edge flags describing the edge to set
* @see #EDGE_LEFT
* @see #EDGE_RIGHT
* @see #EDGE_BOTTOM
*/
public void setShadow(Drawable shadow, int edgeFlag) {
if ((edgeFlag & EDGE_LEFT) != 0) {
mShadowLeft = shadow;
} else if ((edgeFlag & EDGE_RIGHT) != 0) {
mShadowRight = shadow;
} else if ((edgeFlag & EDGE_BOTTOM) != 0) {
mShadowBottom = shadow;
}
invalidate();
}
/**
* Set a drawable used for edge shadow.
*
* @param resId Resource of drawable to use
* @param edgeFlag Combination of edge flags describing the edge to set
* @see #EDGE_LEFT
* @see #EDGE_RIGHT
* @see #EDGE_BOTTOM
*/
public void setShadow(int resId, int edgeFlag) {
setShadow(getResources().getDrawable(resId), edgeFlag);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
if (!mEnable) {
return false;
}
try {
return mDragHelper.shouldInterceptTouchEvent(event);
} catch (ArrayIndexOutOfBoundsException e) {
// FIXME: handle exception
// issues #9
return false;
}
}
@Override
public boolean onTouchEvent(MotionEvent event) {
if (!mEnable) {
return false;
}
mDragHelper.processTouchEvent(event);
return true;
}
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
mInLayout = true;
if (mContentView != null)
mContentView.layout(mContentLeft, mContentTop,
mContentLeft + mContentView.getMeasuredWidth(),
mContentTop + mContentView.getMeasuredHeight());
mInLayout = false;
}
@Override
public void requestLayout() {
if (!mInLayout) {
super.requestLayout();
}
}
@Override
protected boolean drawChild(Canvas canvas, View child, long drawingTime) {
final boolean drawContent = child == mContentView;
boolean ret = super.drawChild(canvas, child, drawingTime);
if (mScrimOpacity > 0 && drawContent
&& mDragHelper.getViewDragState() != ViewDragHelper.STATE_IDLE) {
drawShadow(canvas, child);
drawScrim(canvas, child);
}
return ret;
}
private void drawScrim(Canvas canvas, View child) {
final int baseAlpha = (mScrimColor & 0xff000000) >>> 24;
final int alpha = (int) (baseAlpha * mScrimOpacity);
final int color = alpha << 24 | (mScrimColor & 0xffffff);
if ((mTrackingEdge & EDGE_LEFT) != 0) {
canvas.clipRect(0, 0, child.getLeft(), getHeight());
} else if ((mTrackingEdge & EDGE_RIGHT) != 0) {
canvas.clipRect(child.getRight(), 0, getRight(), getHeight());
} else if ((mTrackingEdge & EDGE_BOTTOM) != 0) {
canvas.clipRect(child.getLeft(), child.getBottom(), getRight(), getHeight());
}
canvas.drawColor(color);
}
private void drawShadow(Canvas canvas, View child) {
final Rect childRect = mTmpRect;
child.getHitRect(childRect);
if ((mEdgeFlag & EDGE_LEFT) != 0) {
mShadowLeft.setBounds(childRect.left - mShadowLeft.getIntrinsicWidth(), childRect.top,
childRect.left, childRect.bottom);
mShadowLeft.setAlpha((int) (mScrimOpacity * FULL_ALPHA));
mShadowLeft.draw(canvas);
}
if ((mEdgeFlag & EDGE_RIGHT) != 0) {
mShadowRight.setBounds(childRect.right, childRect.top,
childRect.right + mShadowRight.getIntrinsicWidth(), childRect.bottom);
mShadowRight.setAlpha((int) (mScrimOpacity * FULL_ALPHA));
mShadowRight.draw(canvas);
}
if ((mEdgeFlag & EDGE_BOTTOM) != 0) {
mShadowBottom.setBounds(childRect.left, childRect.bottom, childRect.right,
childRect.bottom + mShadowBottom.getIntrinsicHeight());
mShadowBottom.setAlpha((int) (mScrimOpacity * FULL_ALPHA));
mShadowBottom.draw(canvas);
}
}
/**
* Scroll out contentView and finish the activity
*/
public void scrollToFinishActivity() {
final int childWidth = mContentView.getWidth();
final int childHeight = mContentView.getHeight();
int left = 0, top = 0;
if ((mEdgeFlag & EDGE_LEFT) != 0) {
left = childWidth + mShadowLeft.getIntrinsicWidth() + OVERSCROLL_DISTANCE;
mTrackingEdge = EDGE_LEFT;
} else if ((mEdgeFlag & EDGE_RIGHT) != 0) {
left = -childWidth - mShadowRight.getIntrinsicWidth() - OVERSCROLL_DISTANCE;
mTrackingEdge = EDGE_RIGHT;
} else if ((mEdgeFlag & EDGE_BOTTOM) != 0) {
top = -childHeight - mShadowBottom.getIntrinsicHeight() - OVERSCROLL_DISTANCE;
mTrackingEdge = EDGE_BOTTOM;
}
mDragHelper.smoothSlideViewTo(mContentView, left, top);
invalidate();
}
public void attachToActivity(Activity activity) {
mActivity = activity;
TypedArray a = activity.getTheme().obtainStyledAttributes(new int[]{
android.R.attr.windowBackground
});
int background = a.getResourceId(0, 0);
a.recycle();
ViewGroup decor = (ViewGroup) activity.getWindow().getDecorView();
ViewGroup decorChild = (ViewGroup) decor.getChildAt(0);
decorChild.setBackgroundResource(background);
decor.removeView(decorChild);
addView(decorChild);
setContentView(decorChild);
decor.addView(this);
}
@Override
public void computeScroll() {
mScrimOpacity = 1 - mScrollPercent;
if (mDragHelper.continueSettling(true)) {
ViewCompat.postInvalidateOnAnimation(this);
}
}
private class ViewDragCallback extends ViewDragHelper.Callback {
private boolean mIsScrollOverValid;
@Override
public boolean tryCaptureView(View view, int i) {
boolean ret = mDragHelper.isEdgeTouched(mEdgeFlag, i);
if (ret) {
if (mDragHelper.isEdgeTouched(EDGE_LEFT, i)) {
mTrackingEdge = EDGE_LEFT;
} else if (mDragHelper.isEdgeTouched(EDGE_RIGHT, i)) {
mTrackingEdge = EDGE_RIGHT;
} else if (mDragHelper.isEdgeTouched(EDGE_BOTTOM, i)) {
mTrackingEdge = EDGE_BOTTOM;
}
if (mListeners != null && !mListeners.isEmpty()) {
for (SwipeListener listener : mListeners) {
listener.onEdgeTouch(mTrackingEdge);
}
}
mIsScrollOverValid = true;
}
boolean directionCheck = false;
if (mEdgeFlag == EDGE_LEFT || mEdgeFlag == EDGE_RIGHT) {
directionCheck = !mDragHelper.checkTouchSlop(ViewDragHelper.DIRECTION_VERTICAL, i);
} else if (mEdgeFlag == EDGE_BOTTOM) {
directionCheck = !mDragHelper
.checkTouchSlop(ViewDragHelper.DIRECTION_HORIZONTAL, i);
} else if (mEdgeFlag == EDGE_ALL) {
directionCheck = true;
}
return ret & directionCheck;
}
@Override
public int getViewHorizontalDragRange(View child) {
return mEdgeFlag & (EDGE_LEFT | EDGE_RIGHT);
}
@Override
public int getViewVerticalDragRange(View child) {
return mEdgeFlag & EDGE_BOTTOM;
}
@Override
public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
super.onViewPositionChanged(changedView, left, top, dx, dy);
if ((mTrackingEdge & EDGE_LEFT) != 0) {
mScrollPercent = Math.abs((float) left
/ (mContentView.getWidth() + mShadowLeft.getIntrinsicWidth()));
} else if ((mTrackingEdge & EDGE_RIGHT) != 0) {
mScrollPercent = Math.abs((float) left
/ (mContentView.getWidth() + mShadowRight.getIntrinsicWidth()));
} else if ((mTrackingEdge & EDGE_BOTTOM) != 0) {
mScrollPercent = Math.abs((float) top
/ (mContentView.getHeight() + mShadowBottom.getIntrinsicHeight()));
}
mContentLeft = left;
mContentTop = top;
invalidate();
if (mScrollPercent < mScrollThreshold && !mIsScrollOverValid) {
mIsScrollOverValid = true;
}
if (mListeners != null && !mListeners.isEmpty()
&& mDragHelper.getViewDragState() == STATE_DRAGGING
&& mScrollPercent >= mScrollThreshold && mIsScrollOverValid) {
mIsScrollOverValid = false;
for (SwipeListener listener : mListeners) {
listener.onScrollOverThreshold();
}
}
if (mScrollPercent >= 1) {
if (!mActivity.isFinishing()) {
mActivity.finish();
mActivity.overridePendingTransition(0, 0);
}
}
}
@Override
public void onViewReleased(View releasedChild, float xvel, float yvel) {
final int childWidth = releasedChild.getWidth();
final int childHeight = releasedChild.getHeight();
int left = 0, top = 0;
if ((mTrackingEdge & EDGE_LEFT) != 0) {
left = xvel > 0 || xvel == 0 && mScrollPercent > mScrollThreshold ? childWidth
+ mShadowLeft.getIntrinsicWidth() + OVERSCROLL_DISTANCE : 0;
} else if ((mTrackingEdge & EDGE_RIGHT) != 0) {
left = xvel < 0 || xvel == 0 && mScrollPercent > mScrollThreshold ? -(childWidth
+ mShadowLeft.getIntrinsicWidth() + OVERSCROLL_DISTANCE) : 0;
} else if ((mTrackingEdge & EDGE_BOTTOM) != 0) {
top = yvel < 0 || yvel == 0 && mScrollPercent > mScrollThreshold ? -(childHeight
+ mShadowBottom.getIntrinsicHeight() + OVERSCROLL_DISTANCE) : 0;
}
mDragHelper.settleCapturedViewAt(left, top);
invalidate();
}
@Override
public int clampViewPositionHorizontal(View child, int left, int dx) {
int ret = 0;
if ((mTrackingEdge & EDGE_LEFT) != 0) {
ret = Math.min(child.getWidth(), Math.max(left, 0));
} else if ((mTrackingEdge & EDGE_RIGHT) != 0) {
ret = Math.min(0, Math.max(left, -child.getWidth()));
}
return ret;
}
@Override
public int clampViewPositionVertical(View child, int top, int dy) {
int ret = 0;
if ((mTrackingEdge & EDGE_BOTTOM) != 0) {
ret = Math.min(0, Math.max(top, -child.getHeight()));
}
return ret;
}
@Override
public void onViewDragStateChanged(int state) {
super.onViewDragStateChanged(state);
if (mListeners != null && !mListeners.isEmpty()) {
for (SwipeListener listener : mListeners) {
listener.onScrollStateChange(state, mScrollPercent);
}
}
}
}
}
swipeBackLayout作为自定义布局继承自FrameLayout，我们需要滑动操作activity和layout，所以和侧滑菜单一样，我们需要去处理滑动中的事件等操作，这里直接使用的是ViewDragHelper来进行view 的滑动操作。对ViewDragHelper 的了解和认识，推荐这篇文章： Android ViewDragHelper完全解析 自定义ViewGroup神器
下面跳到（3）分步骤分析
（3）整个项目的重点SwipeBackLayout的结构分析
3.1 在构造函数中进行初始化，包含ViewDragHelper的初始化，SwipeBackLayout可以设置左右下三个滑动方向，这里也对它三个方向的阴影部分进行初始化。
3.2 自定义滑动的监听SwipeListener接口，使用SwipeBackLayout对象的时候可以通过addSwipeListener增加监听，并且调用其中的三个方法，onScrollStateChange，onEdgeTouch，onScrollOverThreshold。分别对应滑动状态改变，触摸边际，和第一次滑动的比例超出了设置的阀值的时候调用。
3.3 重写触摸的相关方法，这也是使用ViewDragHelper必须实现的步骤，将onInterceptTouchEvent和onTouchEvent交给ViewDragHelper的实例进行处理。
3.4 继承的是FrameLayout所以这里需要重写onLayout和drawChild方法。这里在drawchild方法中也主要是添加了绘制阴影，以及透明背景的操作（当滑动退出activity的时候背景的纱罩效果）。
3.5 scrollToFinishActivity方法，在SwipeBackActivity调用去滑动删除当前activity
3.6 attachToActivity方法，在SwipeBackActivityHelper中调用，完成获取当前的decorView并且将SwipeBackLayout添加到decorView上面，从而实现滑动的时候是对当前整个界面的操作。
3.7 完成步骤1中的ViewDragHelper的CallBack的继承操作，在这里里面根据不同的状态来调用步骤2中的方法。
到这里就对整个的swipeBackLayout进行了解析。
（4）推荐文章：
4.1 返回键最佳继承者：SwipeBack 滑动返回
4.2 Android SwipeBack pattern
4.3 Dragging With ViewDragHelper
4.4 Each Navigation Drawer Hides a ViewDragHelper
4.5 sockeqwe/SwipeBack
4.6 ikew0ng/SwipeBackLayout
4.7 How to Implement a Floating Activity in an Android App