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)

图1 最终效果图

思路分析

1. 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
2. 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
3. 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
4. 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frameworksasepackagesSystemUIsrccomandroidsystemuistatusbarpolicyKeyButtonView.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。