Android6.0 源码修改之 仿IOS添加全屏可拖拽浮窗返回按钮
前言
之前写过屏蔽系统导航栏功能的文章，具体可看Android6.0 源码修改之屏蔽导航栏虚拟按键（Home和RecentAPP）/动态显示和隐藏NavigationBar

在某些特殊定制的版本中要求完全去掉导航栏，那么当用户点进一些系统自带的应用界面如设置、联系人等，就没法退出了，虽然可以在actionBar中添加back按钮，但总不能每一个app都去添加吧。所以灵机一动我们就给系统添加一个全屏可拖拽的浮窗按钮，点击的时候处理返回键的逻辑。它大概长这样(审美可能丑了点，你们可以自由发挥)

在这里插入图片描述
图1 最终效果图

思路分析
通过分析之前的NavigationBar代码，发现系统是通过WindowManager添加View的方式来实现，此处我们也可以模拟这种方法来添加
添加悬浮窗以后监听触摸事件，跟随手指移动重新修改view的layoutParam
松手后获取当前X坐标，小于屏幕width的一半则平移归位至屏幕左边
添加系统的返回按键功能
一、添加悬浮窗
private void showFloatingWindow() {

DisplayMetrics outMetrics = new DisplayMetrics();
mWindowManager.getDefaultDisplay().getMetrics(outMetrics);
screenWidth = outMetrics.widthPixels;
screenHeight = outMetrics.heightPixels;

layoutParams = new WindowManager.LayoutParams();
layoutParams.type = WindowManager.LayoutParams.TYPE_PHONE;
layoutParams.format = PixelFormat.RGBA_8888;
layoutParams.gravity = Gravity.LEFT | Gravity.TOP;
layoutParams.flags = WindowManager.LayoutParams.FLAG_NOT_TOUCH_MODAL | WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;
layoutParams.width = 100;
layoutParams.height = 100;
layoutParams.x = 200;
layoutParams.y = 200;

button = new ImageButton(mContext);
button.setBackground(mContext.getResources().getDrawable(R.drawable.fab_background));//系统通讯录里的蓝色圆形图标
button.setImageResource(R.drawable.ic_sysbar_back);//系统本身的back图标
mWindowManager.addView(button, layoutParams);
isShowFloatingView = true;

}
代码很简单，就是通过windowManager添加一个ImageButton，宽高都是100的，位置在屏幕左上角为原点的200,200。需要注意的是因为我们是在源码里添加，而且是M的版本，所以type为WindowManager.LayoutParams.TYPE_PHONE。如果是在普通的app里注意事项可参考这篇

二、添加触摸事件监听
button.setOnTouchListener(new FloatingOnTouchListener());

private class FloatingOnTouchListener implements View.OnTouchListener {

private int lastX;
private int lastY;

@Override
public boolean onTouch(View view, MotionEvent event) {
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            isDrag = false;
            lastX = (int) event.getRawX();
            lastY = (int) event.getRawY();
            break;

        case MotionEvent.ACTION_MOVE:
            isDrag = true;
            int nowX = (int) event.getRawX();
            int nowY = (int) event.getRawY();
            int movedX = nowX - lastX;
            int movedY = nowY - lastY;
            lastX = nowX;
            lastY = nowY;
            layoutParams.x = layoutParams.x + movedX;
            layoutParams.y = layoutParams.y + movedY;
            //获取当前手指移动的x和y，通过updateViewLayout方法将改变后的x和y设置给button
            mWindowManager.updateViewLayout(view, layoutParams);
            break;

        case MotionEvent.ACTION_UP:
            if (isDrag) {
                log("lastX=" + lastX + "  screenWidth=" + screenWidth);
                //手指抬起时，判断是需要滑动到屏幕左边还是屏幕右边
                if (lastX >= screenWidth / 2) {
                    setAnimation(view, lastX, screenWidth);
                } else {
                    setAnimation(view, -lastX, 0);
                }
            }
            break;
    }
    //返回true则消费事件，返回false则传递事件，此处特殊处理是为了和点击事件区分
    return isDrag || view.onTouchEvent(event);
}

三、添加抬起滑动归位动画
private void setAnimation(final View view, int fromX, int toX) {

    final ValueAnimator animator = ValueAnimator.ofInt(fromX, toX);
    if (Math.abs(fromX) < screenWidth / 4 || fromX > screenWidth * 3 / 4)
        animator.setDuration(300);
    else
        animator.setDuration(600);

    animator.setInterpolator(new LinearInterpolator());
    animator.addListener(new Animator.AnimatorListener() {
        @Override
        public void onAnimationStart(Animator animation) {}
        @Override
        public void onAnimationEnd(Animator animation) {
            log("onAnimationEnd=");
            savePreValue(layoutParams.x, layoutParams.y);
        }
        @Override
        public void onAnimationCancel(Animator animation) {}
        @Override
        public void onAnimationRepeat(Animator animation) {}
    });
    animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
        @Override
        public void onAnimationUpdate(ValueAnimator animation) {
            int current = (int) animator.getAnimatedValue();
            log("current=" + current);

            layoutParams.x = Math.abs(current);
            mWindowManager.updateViewLayout(view, layoutParams);
        }
    });
    animator.start();
}

}
同样是通过改变button的x和y值来达到滑动效果，只不过我只需要x平移，y为0，需要斜着滑的你们可自由发挥，为了使滑动看上去平滑，给动画添加了一个线性插值器，设置滑动时间，监听返回插值进度，这样动态设置给button。为了保存button的最终位置，添加了一个动画完成监听，并将x和y写入到SharedPreferences中保存。

四、添加点击返回功能
通过打印日志分析，系统导航栏的返回按键，发现其原理是通过KeyButtonView的触摸事件发送一个KeyEvent事件给系统来实现返回功能

源码位置frameworksbasepackagesSystemUIsrccomandroidsystemuistatusbarpolicyKeyButtonView.java

public boolean onTouchEvent(MotionEvent ev) {

final int action = ev.getAction();
int x, y;
if (action == MotionEvent.ACTION_DOWN) {
    mGestureAborted = false;
}
if (mGestureAborted) {
    return false;
}

switch (action) {
    case MotionEvent.ACTION_DOWN:
        //按下的时间
        mDownTime = SystemClock.uptimeMillis();
        setPressed(true);
        if (mCode != 0) {//按下事件
            sendEvent(KeyEvent.ACTION_DOWN, 0, mDownTime);
        } else {
            // Provide the same haptic feedback that the system offers for virtual keys.
            performHapticFeedback(HapticFeedbackConstants.VIRTUAL_KEY);
        }
        removeCallbacks(mCheckLongPress);
        postDelayed(mCheckLongPress, ViewConfiguration.getLongPressTimeout());
        break;
    case MotionEvent.ACTION_MOVE:
        x = (int)ev.getX();
        y = (int)ev.getY();
        setPressed(x >= -mTouchSlop
                && x < getWidth() + mTouchSlop
                && y >= -mTouchSlop
                && y < getHeight() + mTouchSlop);
        break;
    case MotionEvent.ACTION_CANCEL:
        setPressed(false);
        if (mCode != 0) {
            sendEvent(KeyEvent.ACTION_UP, KeyEvent.FLAG_CANCELED);
        }
        removeCallbacks(mCheckLongPress);
        break;
    case MotionEvent.ACTION_UP:
        final boolean doIt = isPressed();
        setPressed(false);
        if (mCode != 0) {
            if (doIt) {//抬起事件
                sendEvent(KeyEvent.ACTION_UP, 0);
                sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
                playSoundEffect(SoundEffectConstants.CLICK);
            } else {
                sendEvent(KeyEvent.ACTION_UP, KeyEvent.FLAG_CANCELED);
            }
        } else {
            // no key code, just a regular ImageView
            if (doIt) {
                performClick();
            }
        }
        removeCallbacks(mCheckLongPress);
        break;
}

return true;

}

//以下为我们给button添加的点击事件
private void sendEvent(int action, int flags, long when) {

int mCode = 4;
Log.e(TAG, "mCode="+mCode + "  flags="+flags);
final int repeatCount = (flags & KeyEvent.FLAG_LONG_PRESS) != 0 ? 1 : 0;
final KeyEvent ev = new KeyEvent(when - 100, when, action, mCode, repeatCount,
        0, KeyCharacterMap.VIRTUAL_KEYBOARD, 0,
        flags | KeyEvent.FLAG_FROM_SYSTEM | KeyEvent.FLAG_VIRTUAL_HARD_KEY,
        InputDevice.SOURCE_KEYBOARD);
InputManager.getInstance().injectInputEvent(ev,
        InputManager.INJECT_INPUT_EVENT_MODE_ASYNC);

}

button.setOnClickListener(new View.OnClickListener() {

    @Override
    public void onClick(View v) {
        Log.e(TAG,"click dragButton ...");
        final long mDownTime = SystemClock.uptimeMillis();
        //onBackPressed();
        sendEvent(KeyEvent.ACTION_DOWN, 0, mDownTime);

        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                sendEvent(KeyEvent.ACTION_UP, 0, SystemClock.uptimeMillis());
            }
        }, 300);
    }
});

需要注意的地方，系统返回键对应的code为4，所以mCode=4，KeyButtonView的触摸事件包含按下和抬起，所以我们只需模拟发送按下和抬起事件，可以看到抬起事件加了300ms的延时发送，这是关键不然系统不会处理。
原文地址https://www.cnblogs.com/cczheng-666/p/10741082.html