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*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

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*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frameworks\base\packages\systemui\src\com\android\systemui\statusbar\policy\keybuttonview.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。