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Android 窗口焦点介绍

背景

我们经常会遇到一种Application does not hava focused window的ANR异常，这种异常一般是没有焦点窗口FocusedWindow导致,且这类异常只会发生在key事件的派发，因为key事件是需要找到一个焦点窗口然后再派发，而触摸事件只需要找到当前显示的窗口即可

焦点窗口设定

WMS只管理窗口，无法确定是否有窗口盖住当前画面。 SurfaceFlinger管理显示，最贴近于用户看到的画面，可以知道是否有窗口盖住当前画面，根据真实的显示窗口设置对应的window信息给InputDispatcher。

关键日志

window

在dumpsys window中查看mCurrentFocus和mFocusedApp

  mCurrentFocus=Window{f96644 u0 NotificationShade}
  mFocusedApp=ActivityRecord{e9566ee u0 com.android.launcher3/.uioverrides.QuickstepLauncher} t12}

mCurrentFocus 指的是当前的焦点窗口
mFocusedApp 指的是当前的焦点Activity

查看有没有LAST ANR

WINDOW MANAGER LAST ANR (dumpsys window lastanr)
  <no ANR has occurred since boot>

这里没有LAST ANR，如果有，mCurrentFocus会显示null

SurfaceFlinger

在dumpsys SurfaceFlinger中查看 HWC layers

Display 4619827259835644672 (active) HWC layers:
---------------------------------------------------------------------------------------------------------------------------------------------------------------
 Layer name
           Z |  Window Type |  Comp Type |  Transform |   Disp Frame (LTRB) |          Source Crop (LTRB) |     Frame Rate (Explicit) (Seamlessness) [Focused]
---------------------------------------------------------------------------------------------------------------------------------------------------------------
 com.example.mysystemdialog/com.example.mysystemdialog.MainActivity#118
  rel      0 |            1 |     CLIENT |          0 |    0    0 1440 2960 |    0.0    0.0 1440.0 2960.0 |                                              [*]
---------------------------------------------------------------------------------------------------------------------------------------------------------------
 StatusBar#75
  rel      0 |         2000 |     CLIENT |          0 |    0    0 1440   84 |    0.0    0.0 1440.0   84.0 |                                              [ ]
---------------------------------------------------------------------------------------------------------------------------------------------------------------
 NavigationBar0#74
  rel      0 |         2019 |     CLIENT |          0 |    0 2792 1440 2960 |    0.0    0.0 1440.0  168.0 |                                              [ ]
---------------------------------------------------------------------------------------------------------------------------------------------------------------

[Focused] 这一列有带[*]号，则说明是焦点窗口

input

在dumpsys input中查看FocusedApplications和FocusedWindows

  FocusedApplications:
    displayId=0, name='ActivityRecord{e9566ee u0 com.android.launcher3/.uioverrides.QuickstepLauncher} t12}', dispatchingTimeout=5000ms
  FocusedWindows:
    displayId=0, name='f96644 NotificationShade'

如果发生ANR，焦点窗口以dumpsys input为主

Input Dispatcher State at time of last ANR:
    ANR:
        Time:......
        Reason:......
        Window:......
    FocusedApplications:......
    FocusedWindows: <none>

event log

05-18 19:22:55.806   580   607 I input_focus: [Focus request f96644 NotificationShade,reason=UpdateInputWindows]
05-18 19:22:55.837   580   675 I input_focus: [Focus leaving e225d94 com.android.launcher3/com.android.launcher3.uioverrides.QuickstepLauncher (server),reason=Waiting for window because NO_WINDOW]
05-18 19:22:55.855   580   675 I input_focus: [Focus entering f96644 NotificationShade (server),reason=Window became focusable. Previous reason: NOT_VISIBLE]

request 和 entering正常情况下是一一对应，打印了entering则表示真正的焦点已经进入到对应的窗口。 发生Application does not hava focused window时，一般request 有打印，我们可以通过是否有entering的打印来分析。 - entering部分有打印，代表焦点已经在input里面，但是仍然有ANR，就需要从input等方面分析。 - entering部分未打印，代表input没有被触发焦点窗口设置到input，需排查SurfaceFlinger或WMS。

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