原文链接: http://www.jianshu.com/p/7b0dfd2bf011#

实现Activity滑动退出

很多应用在二级详情页面加入了滑动退出activity的效果，很方便，心血来潮，想着自己也来实现这个效果，就当做练手吧。

实现View的滑动有很多种方法，如自己在onTouchEvent中处理触摸事件，然后滚动View到相应位置，也可以用google V4包为我们提供的ViewDragHelper来处理触摸事件，我们这里选择后者，因为滑动退出操作都是在屏幕的边缘时触发，而ViewDragHelper刚好提供了想要的实现，可以说利用ViewDragHelper来实现我们的需求非常简单。

先定义一个ViewGroup，并做一些必要的变量声明
BaseSwipeLayout

  public class BaseSwipeLayout extends FrameLayout{    private View mDragView;    private ViewDragHelper mViewDragHelper;    private Point mAutoBackOrignalPoint = new Point();    private Point mCurArrivePoint = new Point();    private int mCurEdgeFlag = ViewDragHelper.EDGE_LEFT;    private int mSwipeEdge = ViewDragHelper.EDGE_LEFT;    public BaseSwipeLayout(Context context) {        this(context, null);    }    public BaseSwipeLayout(Context context, AttributeSet attrs) {        this(context, attrs, 0);    }    public BaseSwipeLayout(Context context, AttributeSet attrs, int defStyleAttr) {        super(context, attrs, defStyleAttr);        init();    } }

既然使用ViewDragHelper，我们把触摸事件交给ViewDragHelper处理，ViewDragHelper不熟悉的同学，相关知识，网上一大堆，自行查看

    @Override    public boolean onInterceptTouchEvent(MotionEvent ev) {        return mViewDragHelper.shouldInterceptTouchEvent(ev);    }    @Override    public boolean onTouchEvent(MotionEvent event) {        mViewDragHelper.processTouchEvent(event);        return true;    }

下面对ViewDragHelper的配置，比较简单，大家看代码吧。

private void init() {        mViewDragHelper = ViewDragHelper.create(this, 1.0f, new ViewDragHelper.Callback() {            @Override            public boolean tryCaptureView(View child, int pointerId) {                return false;            }            @Override            public int clampViewPositionHorizontal(View child, int left, int dx) {                mCurArrivePoint.x = left;                //允许左右触发滑动，否则return 0                if (mCurEdgeFlag != ViewDragHelper.EDGE_BOTTOM) {                    return left;                }else return 0;            }            @Override            public int clampViewPositionVertical(View child, int top, int dy) {                mCurArrivePoint.y = top;                //允许底部触发滑动，否则return 0                if (mCurEdgeFlag == ViewDragHelper.EDGE_BOTTOM) {                    return top;                }else return 0;            }            @Override            public void onViewReleased(View releasedChild, float xvel, float yvel) {                super.onViewReleased(releasedChild, xvel, yvel);                switch (mCurEdgeFlag) {                    case ViewDragHelper.EDGE_LEFT:                        //水平滑动超过一半，触发结束                        if (mCurArrivePoint.x > getWidth()/2) {                            mViewDragHelper.settleCapturedViewAt(getWidth(), mAutoBackOrignalPoint.y);                        }else {                            mViewDragHelper.settleCapturedViewAt(mAutoBackOrignalPoint.x, mAutoBackOrignalPoint.y);                        }                        break;                    case ViewDragHelper.EDGE_RIGHT:                        //水平滑动超过一半，触发结束                        if (mCurArrivePoint.x < -getWidth()/2) {                            mViewDragHelper.settleCapturedViewAt(-getWidth(), mAutoBackOrignalPoint.y);                        }else {                            mViewDragHelper.settleCapturedViewAt(mAutoBackOrignalPoint.x, mAutoBackOrignalPoint.y);                        }                        break;                    case ViewDragHelper.EDGE_BOTTOM:                        //垂直滑动超过一半，触发结束                        if (mCurArrivePoint.y < -getHeight()/2) {                            mViewDragHelper.settleCapturedViewAt(mAutoBackOrignalPoint.x, -getHeight());                        }else {                            mViewDragHelper.settleCapturedViewAt(mAutoBackOrignalPoint.x, mAutoBackOrignalPoint.y);                        }                        break;                }                mCurArrivePoint.x = 0;                mCurArrivePoint.y = 0;                invalidate();            }            @Override            public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {                super.onViewPositionChanged(changedView, left, top, dx, dy);                switch (mCurEdgeFlag) {                    case ViewDragHelper.EDGE_LEFT:                        if (left >= getWidth()) {                            if (mFinishScroll != null) {                                mFinishScroll.complete();                            }                        }                        break;                    case ViewDragHelper.EDGE_RIGHT:                        if (left <= -getWidth()) {                            if (mFinishScroll != null) {                                mFinishScroll.complete();                            }                        }                        break;                    case ViewDragHelper.EDGE_BOTTOM:                        if (top <= -getHeight()) {                            if (mFinishScroll != null) {                                mFinishScroll.complete();                            }                        }                        break;                }            }            @Override            public void onEdgeDragStarted(int edgeFlags, int pointerId) {                mCurEdgeFlag = edgeFlags;                if (mDragView == null) mDragView = getChildAt(0);                mViewDragHelper.captureChildView(mDragView, pointerId);            }        });        mViewDragHelper.setEdgeTrackingEnabled(ViewDragHelper.EDGE_LEFT);    }

这里还有个步骤不要忘了，手指离开屏幕或者滑动超过屏幕的时候，我们触发了ViewGroup自行完全滚动出屏幕的调用，所以我们需要在computeScroll中做检查，如果滚动没有结束，刷新View，继续滚动。

    @Override    public void computeScroll() {        if (mViewDragHelper.continueSettling(true)) {            invalidate();        }    }

这样我们自定义的BaseSwipeLayout打造完毕，我们把它设为activity的根布局测试一下

<?xml version="1.0" encoding="utf-8"?><com.aliouswang.swipeback.widget.BaseSwipeLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:orientation="vertical" android:layout_width="match_parent"    android:id="@+id/swipe_layout"    android:layout_height="match_parent">    <ScrollView        android:layout_width="match_parent"        android:layout_height="match_parent">        <LinearLayout            android:orientation="vertical"            android:layout_width="match_parent"            android:layout_height="wrap_content">            <TextView                android:text="Swipe Back Demo"                android:gravity="center"                android:textColor="@android:color/white"                android:background="@android:color/holo_red_light"                android:layout_width="match_parent"                android:layout_height="100dp" />            <TextView                android:text="Swipe Back Demo"                android:gravity="center"                android:textColor="@android:color/white"                android:background="@android:color/holo_blue_light"                android:layout_width="match_parent"                android:layout_height="100dp" />            <TextView                android:text="Swipe Back Demo"                android:gravity="center"                android:textColor="@android:color/white"                android:background="@android:color/holo_green_light"                android:layout_width="match_parent"                android:layout_height="100dp" />            <TextView                android:text="Swipe Back Demo"                android:gravity="center"                android:textColor="@android:color/white"                android:background="@android:color/holo_purple"                android:layout_width="match_parent"                android:layout_height="100dp" />            <TextView                android:text="Swipe Back Demo"                android:gravity="center"                android:textColor="@android:color/white"                android:background="@android:color/holo_green_dark"                android:layout_width="match_parent"                android:layout_height="100dp" />            <TextView                android:text="Swipe Back Demo"                android:gravity="center"                android:textColor="@android:color/white"                android:background="@android:color/holo_red_dark"                android:layout_width="match_parent"                android:layout_height="100dp" />            <TextView                android:text="Swipe Back Demo"                android:gravity="center"                android:textColor="@android:color/white"                android:background="@android:color/holo_blue_dark"                android:layout_width="match_parent"                android:layout_height="100dp" />            <TextView                android:text="Swipe Back Demo"                android:gravity="center"                android:textColor="@android:color/white"                android:background="@android:color/holo_orange_dark"                android:layout_width="match_parent"                android:layout_height="100dp" />        </LinearLayout>    </ScrollView></com.aliouswang.swipeback.widget.BaseSwipeLayout>

当然，我们已经实现了整个功能，但是有一点很不爽的是，我们必须将BaseSwipeLayout作为布局的根，这样实现还不够优雅，我们能不能不改变我们原有的布局文件，却依然能加入滑动退出功能。
这里我们要介绍一个DecorView，它是Window的最顶层View，它含有一个子LinearLayout，代表整个Window，包括通知栏，状态栏，内容显示区域，所以我们activity页面是DecorView的子View的子View，那么我们能不能直接给DecorView的子View添加到我们的BaseSwipeLayout，再将BaseSwipeLayout添加到DecorView，当然是可以的，而且这种方式，我们不需要改变原来的布局文件，更加优雅。

我们定义一个SwipeHelper类，辅助我们进行BaseSwipeLayout插入操作。

public class SwipeHelper {    private Activity mActivity;    private BaseSwipeLayout mBaseSwipeLayout;    public SwipeHelper(Activity activity) {        this.mActivity = activity;    }    public void onActivityCreate() {        mBaseSwipeLayout = (BaseSwipeLayout) LayoutInflater.from(mActivity)                .inflate(R.layout.swipe_layout, null);        mBaseSwipeLayout.setOnFinishScroll(new BaseSwipeLayout.OnFinishScroll() {            @Override            public void complete() {                mActivity.finish();            }        });    }    public void onPostCreate() {        mBaseSwipeLayout.attachToActivity(mActivity);    }    public void setSwipeEdge(int edgeFlag) {        mBaseSwipeLayout.setSwipeEdge(edgeFlag);    }}

BaseSwipeLayout

//核心代码，绑定到相应activity    public void attachToActivity(Activity activity) {        this.mActivity = activity;        TypedArray a = activity.getTheme().obtainStyledAttributes(new int[]{                android.R.attr.windowBackground        });        int background = a.getResourceId(0, 0);        a.recycle();        ViewGroup decorView = (ViewGroup) activity.getWindow().getDecorView();        ViewGroup decorChild = (ViewGroup) decorView.getChildAt(0);        decorChild.setBackgroundResource(background);        decorView.removeView(decorChild);        addView(decorChild);        decorView.addView(this);    }

需要添加滑动退出的activity，添加想要代码

    private SwipeHelper mSwipeHelper;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.view_drag_helper_act_layout);        mSwipeHelper = new SwipeHelper(this);        mSwipeHelper.onActivityCreate();        mSwipeHelper.setSwipeEdge(ViewDragHelper.EDGE_RIGHT);    }    @Override    protected void onPostCreate(Bundle savedInstanceState) {        super.onPostCreate(savedInstanceState);        mSwipeHelper.onPostCreate();    }

2016-02-23 15_17_01.gif

到此我们的代码基本完成，源码我放到了BaseSwipe，欢迎指教！

参考：https://github.com/ikew0ng/SwipeBackLayout

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下面为我遇见的问题及我的解决方案:

问题:滑动退出时的背景是白色的，而不是下层的页面.

答: 首先看你的activity是继承于Activity还是AppCompatActivity.
1.是Activity,在清单文件中你这个Activity标签里写下:android:theme="@android:style/Theme.Translucent.NoTitleBar".
2.是AppCompatActivity,用自定义透明背景.在style.xml里定义

<style name="NoTitleTranslucentTheme" parent="AppTheme"><item name="android:windowNoTitle">true</item><!-- 看你要不要title决定加不加这行 --><item name="android:windowBackground">@android:color/transparent</item><item name="android:windowIsTranslucent">true</item></style>

然后同上,在清单文件声明这个activity的标签里引用就好了.
<activity android:name=".ui.activity.xxxActivity" android:theme="@style/NoTitleTranslucentTheme"/>