Android-侧滑返回方案简析

前言

自从iOS提供了侧滑返回上一级页面功能之后，Android很多应用也开始跟风，美其名曰：保证体验上的统一。作为开发者，当然得研究一下如何实现。

方案1-透明activity

将activity背景色设置成透明，滑动时，将activity-content-view跟随侧滑。

优点

原理易懂
实现简单

缺点

会影响activity生命周期（经测试，不会走到上一个activity-onStop，这篇回答微信（Android）左滑 finish activity 这个是怎么实现的?说不会走到onPause是不对的。
对性能有一定影响（Hidden Cost of Transparency ，Android性能优化典范 - 第2季）

实战

我们可以用如下代码实现一个简化版本的侧滑返回：

public class SlideBackActivity extends AppCompatActivity {
    private boolean mFinishAfterAnimate;
    private float mLastDownPointX;
    private boolean mIsSliding;
    private View mContentView;
    private int mScreenWidth;
    private int mTouchSlop;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        Log.e("kkk", "SlideBackActivity-onCreate");
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_slide_back);
        mContentView = findViewById(Window.ID_ANDROID_CONTENT);
        mTouchSlop = ViewConfiguration.get(this).getScaledTouchSlop();
        mScreenWidth = getResources().getDisplayMetrics().widthPixels;
    }
    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        final int action = ev.getAction() & MotionEvent.ACTION_MASK;
        switch (action) {
            case MotionEvent.ACTION_DOWN:
                mLastDownPointX = ev.getRawX();
                mFinishAfterAnimate = false;
                mIsSliding = true;
                break;
            case MotionEvent.ACTION_MOVE:
                final float curPointX = ev.getRawX();
                if (mIsSliding) {
                    if(Math.abs(curPointX - mLastDownPointX) > mTouchSlop) {
                        mContentView.setX(Math.abs(curPointX - mLastDownPointX));
                    }
                }
                break;
            case MotionEvent.ACTION_UP:
                final float currentPointX = ev.getRawX();
                if(Math.abs(currentPointX - mLastDownPointX) > 500) {
                    mFinishAfterAnimate = true;
                    animateContentView(Math.abs(currentPointX - mLastDownPointX), mScreenWidth);
                } else {
                    mFinishAfterAnimate = false;
                    animateContentView(Math.abs(currentPointX - mLastDownPointX), 0);
                }
                mIsSliding = false;
                break;
        }
        return super.dispatchTouchEvent(ev);
    }
    private void animateContentView(float start, float end) {
        ObjectAnimator anim1 = ObjectAnimator.ofFloat(mContentView, "x", start, end);
        AnimatorSet animSet = new AnimatorSet();
        animSet.setInterpolator(new LinearInterpolator());
        animSet.setDuration(100);
        animSet.playTogether(anim1);
        if (mFinishAfterAnimate) {
            animSet.addListener(new Animator.AnimatorListener() {
                @Override
                public void onAnimationStart(Animator animation) {
                }
                @Override
                public void onAnimationEnd(Animator animation) {
                    finish();
                }
                @Override
                public void onAnimationCancel(Animator animation) {
                }
                @Override
                public void onAnimationRepeat(Animator animation) {
                }
            });
        }
        animSet.start();
    }
    @Override
    public void finish() {
        super.finish();
        if (mFinishAfterAnimate) overridePendingTransition(0,0);
    }
    @Override
    protected void onStart() {
        Log.e("kkk", "SlideBackActivity-onStart");
        super.onStart();
    }
    @Override
    protected void onResume() {
        Log.e("kkk", "SlideBackActivity-onResume");
        super.onResume();
    }
    @Override
    protected void onPause() {
        Log.e("kkk", "SlideBackActivity-onPause");
        super.onPause();
    }
    @Override
    protected void onStop() {
        Log.e("kkk", "SlideBackActivity-onStop");
        super.onStop();
    }
    @Override
    protected void onDestroy() {
        Log.e("kkk", "SlideBackActivity-onDestroy");
        super.onDestroy();
    }
}

当然了，前提还是得把activity主题设置成透明

<style name="Transparent" parent="Theme.AppCompat.Light.NoActionBar">
    <item name="android:windowBackground">@android:color/transparent</item>
    <item name="android:windowIsTranslucent">true</item>
</style>

通过下方日志我们可以看到，启动SlideBackAcitvity时，上一个activity(main)-onStop方法没有走到，而退出SlideBackAcitvity后，上一个activity(main)-onStart方法也没有走到。

03-02 15:28:54.790 1531-1531/com.mason.swipebackdemo E/kkk: main-onStart
03-02 15:28:54.799 1531-1531/com.mason.swipebackdemo E/kkk: main-onResume
03-02 15:29:11.439 1531-1531/com.mason.swipebackdemo E/kkk: main-onPause
03-02 15:29:11.447 1531-1531/com.mason.swipebackdemo E/kkk: SlideBackActivity-onCreate
03-02 15:29:11.452 1531-1531/com.mason.swipebackdemo E/kkk: SlideBackActivity-onStart
03-02 15:29:11.453 1531-1531/com.mason.swipebackdemo E/kkk: SlideBackActivity-onResume
03-02 15:29:16.905 1531-1531/com.mason.swipebackdemo E/kkk: SlideBackActivity-onPause
03-02 15:29:16.924 1531-1531/com.mason.swipebackdemo E/kkk: main-onResume
03-02 15:29:16.966 1531-1531/com.mason.swipebackdemo E/kkk: SlideBackActivity-onStop
03-02 15:29:16.966 1531-1531/com.mason.swipebackdemo E/kkk: SlideBackActivity-onDestroy