前言
Android无需权限显示悬浮窗, 兼谈逆向分析app这篇文章阅读量很大, 这篇文章是通过逆向分析UC浏览器的实现和兼容性处理来得到一个悬浮窗的实现小技巧, 但有很多问题没有弄明白, 比如为什么在API 18及以下TYPE_TOAST的悬浮窗无法接受触摸事件, 为什么使用TYPE_TOAST就不需要权限.
期间@廖祜秋liaohuqiu_秋百万和我有较多探讨, 原文贴的一个demo android-UCToast也是他做的, 他也有写Android 悬浮窗的小结. 这几篇关于悬浮窗的文章, 是我和他共同探索的结果, 非常感谢.
思路
老实说一开始我是想看看整个事件的传播过程, 从EventHub开始, 到View.onTouchEvent, 想看看Android系统内事件分发, 不过由于绝大部分代码在Native层, 我并没有搞清楚.
其实要想知道原因很简单, 只要grep一下TYPE_TOAST, 把每个用到的地方看一看, 自然就知道了, 但是恰好周末我手上没有源码, 只能在grepcode上面一个一个的查, 所以也花了不少时间.
正文
还是从最简单的地方开始, 我们调用了WindowManager.addView, WindowManager是个接口, 我们使用的是他的实现类WindowManagerImpl, 看看它的addView方法:
@Override
public void addView(View view, ViewGroup.LayoutParams params) {
mGlobal.addView(view, params, mDisplay, mParentWindow);
}
mGlobal是WindowManagerGlobal的实例, 再看看WindowManagerGlobal.addView:
public void addView(View view, ViewGroup.LayoutParams params,
Display display, Window parentWindow) {
......
final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams)params;
......
synchronized (mLock) {
......
root = new ViewRootImpl(view.getContext(), display);
view.setLayoutParams(wparams);
......
}
// do this last because it fires off messages to start doing things
try {
root.setView(view, wparams, panelParentView);
} catch (RuntimeException e) {
// BadTokenException or InvalidDisplayException, clean up.
......
}
代码中创建了一个ViewRootImpl, 调用了它的setView, 将我们要添加的view传入. 继续看ViewRootImpl.setView:
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
synchronized (this) {
if (mView == null) {
......
mWindowAttributes.copyFrom(attrs);
if (mWindowAttributes.packageName == null) {
mWindowAttributes.packageName = mBasePackageName;
}
......
try {
......
res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(),
mAttachInfo.mContentInsets, mInputChannel);
} catch (RemoteException e) {
......
throw new RuntimeException("Adding window failed", e);
} finally {
......
}
......
}
}
}
对我们的分析来说最关键的代码是
res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(),
mAttachInfo.mContentInsets, mInputChannel);
mWindowSession的类型是IWindowSession, mWindow的类型是IWindow.Stub, 这句代码就是利用AIDL进行IPC, 实际被调用的是Session.addToDisplay:
@Override
public int addToDisplay(IWindow window, int seq, WindowManager.LayoutParams attrs,
int viewVisibility, int displayId, Rect outContentInsets,
InputChannel outInputChannel) {
return mService.addWindow(this, window, seq, attrs, viewVisibility, displayId,
outContentInsets, outInputChannel);
}
mService是WindowManagerService, 继续往下跟:
public int addWindow(Session session, IWindow client, int seq,
WindowManager.LayoutParams attrs, int viewVisibility, int displayId,
Rect outContentInsets, InputChannel outInputChannel) {
int[] appOp = new int[1];
int res = mPolicy.checkAddPermission(attrs, appOp);
if (res != WindowManagerGlobal.ADD_OKAY) {
return res;
}
......
final int type = attrs.type;
synchronized(mWindowMap) {
......
mPolicy.adjustWindowParamsLw(win.mAttrs);
......
}
......
return res;
}
mPolicy是标记为final的成员变量:
final WindowManagerPolicy mPolicy = PolicyManager.makeNewWindowManager();
继续看PolicyManager.makeNewWindowManager:
public final class PolicyManager {
private static final String POLICY_IMPL_CLASS_NAME =
"com.android.internal.policy.impl.Policy";
private static final IPolicy sPolicy;
static {
// Pull in the actual implementation of the policy at run-time
try {
Class policyClass = Class.forName(POLICY_IMPL_CLASS_NAME);
sPolicy = (IPolicy)policyClass.newInstance();
} catch (ClassNotFoundException ex) {
throw new RuntimeException(
POLICY_IMPL_CLASS_NAME + " could not be loaded", ex);
} catch (InstantiationException ex) {
throw new RuntimeException(
POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
} catch (IllegalAccessException ex) {
throw new RuntimeException(
POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
}
}
// Cannot instantiate this class
private PolicyManager() {}
......
public static WindowManagerPolicy makeNewWindowManager() {
return sPolicy.makeNewWindowManager();
}
......
}
这里sPolicy是com.android.internal.policy.impl.Policy对象, 再看看它的makeNewWindowManager方法返回的是什么:
public WindowManagerPolicy makeNewWindowManager() {
return new PhoneWindowManager();
}
现在我们知道mPolicy实际上是PhoneWindowManager, 那么
int res = mPolicy.checkAddPermission(attrs, appOp);
实际调用的代码是:
@Override
public int checkAddPermission(WindowManager.LayoutParams attrs, int[] outAppOp) {
int type = attrs.type;
outAppOp[0] = AppOpsManager.OP_NONE;
if (type < WindowManager.LayoutParams.FIRST_SYSTEM_WINDOW
|| type > WindowManager.LayoutParams.LAST_SYSTEM_WINDOW) {
return WindowManagerGlobal.ADD_OKAY;
}
String permission = null;
switch (type) {
case TYPE_TOAST:
// XXX right now the app process has complete control over
// this... should introduce a token to let the system
// monitor/control what they are doing.
break;
case TYPE_DREAM:
case TYPE_INPUT_METHOD:
case TYPE_WALLPAPER:
case TYPE_PRIVATE_PRESENTATION:
// The window manager will check these.
break;
case TYPE_PHONE:
case TYPE_PRIORITY_PHONE:
case TYPE_SYSTEM_ALERT:
case TYPE_SYSTEM_ERROR:
case TYPE_SYSTEM_OVERLAY:
permission = android.Manifest.permission.SYSTEM_ALERT_WINDOW;
outAppOp[0] = AppOpsManager.OP_SYSTEM_ALERT_WINDOW;
break;
default:
permission = android.Manifest.permission.INTERNAL_SYSTEM_WINDOW;
}
if (permission != null) {
if (mContext.checkCallingOrSelfPermission(permission)
!= PackageManager.PERMISSION_GRANTED) {
return WindowManagerGlobal.ADD_PERMISSION_DENIED;
}
}
return WindowManagerGlobal.ADD_OKAY;
}
我截取的是4.4_r1的代码, 我们最关心的部分其实一直没有变, 那就是TYPE_TOAST根本没有做权限检查, 直接break出去了, 最后返回WindowManagerGlobal.ADD_OKAY.
不需要权限显示悬浮窗的原因已经找到了, 接着刚才addWindow方法的分析, 继续看下面一句:
mPolicy.adjustWindowParamsLw(win.mAttrs);
也就是PhoneWindowManager.adjustWindowParamsLw, 注意这里我给出了三个版本的实现, 一个是2.0到2.3.7实现的版本, 一个是4.0.1到4.3.1实现的版本, 一个是4.4实现的版本:
//Android 2.0 - 2.3.7 PhoneWindowManager
public void adjustWindowParamsLw(WindowManager.LayoutParams attrs) {
switch (attrs.type) {
case TYPE_SYSTEM_OVERLAY:
case TYPE_SECURE_SYSTEM_OVERLAY:
case TYPE_TOAST:
// These types of windows can't receive input events.
attrs.flags |= WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
| WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE;
break;
}
}
//Android 4.0.1 - 4.3.1 PhoneWindowManager
public void adjustWindowParamsLw(WindowManager.LayoutParams attrs) {
switch (attrs.type) {
case TYPE_SYSTEM_OVERLAY:
case TYPE_SECURE_SYSTEM_OVERLAY:
case TYPE_TOAST:
// These types of windows can't receive input events.
attrs.flags |= WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
| WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE;
attrs.flags &= ~WindowManager.LayoutParams.FLAG_WATCH_OUTSIDE_TOUCH;
break;
}
}
//Android 4.4 PhoneWindowManager
@Override
public void adjustWindowParamsLw(WindowManager.LayoutParams attrs) {
switch (attrs.type) {
case TYPE_SYSTEM_OVERLAY:
case TYPE_SECURE_SYSTEM_OVERLAY:
// These types of windows can't receive input events.
attrs.flags |= WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
| WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE;
attrs.flags &= ~WindowManager.LayoutParams.FLAG_WATCH_OUTSIDE_TOUCH;
break;
}
}
grepcode上没有3.x的代码, 我也没查具体是什么, 没必要考虑3.x.
可以看到, 在4.0.1以前, 当我们使用TYPE_TOAST, Android会偷偷给我们加上FLAG_NOT_FOCUSABLE和FLAG_NOT_TOUCHABLE, 4.0.1开始, 会额外再去掉FLAG_WATCH_OUTSIDE_TOUCH, 这样真的是什么事件都没了. 而4.4开始, TYPE_TOAST被移除了, 所以从4.4开始, 使用TYPE_TOAST的同时还可以接收触摸事件和按键事件了, 而4.4以前只能显示出来, 不能交互.
API level 18及以下使用TYPE_TOAST无法接收触摸事件的原因也找到了.
尾声
原文发的时候很多事情没搞清楚, 后来文章编辑了十几次, 加上这篇文章, 基本上把所有的疑问都搞明白了. 嗯, 关于这个神奇的悬浮窗的事情应该到这里就结束了.
本人水平有限, 如有错误, 欢迎指正, 以免误导他人
