IWindowManager - call setOverscan via reflection

Question

I'm running a device with android pie and want to programmatically change the overscan from within my app. Therefore I've done following:

• granted my app WRITE_SECURE_SETTINGS via adb

Problem

The code here let's me believe, that there should be a setOverscan method inside the IWindowManager$Stub but there isn't. Am I doing something wrong or is it just not possible to do what I want to do the way I try to do it?

My code shows that hasNavigationBar is working, but the setOverscanMode method isn't and fails with java.lang.NoSuchMethodException: android.view.IWindowManager$Stub$Proxy.setOverscan [int, int, int, int, int]

Code

object WindowTool {

    // WindowManager source code: https://android.googlesource.com/platform/frameworks/base/+/master/core/java/android/view/IWindowManager.aidl

    fun getWindowManagerService(): Any {
        val serviceManager = Class.forName("android.os.ServiceManager")
        val serviceBinder = serviceManager.getMethod("getService", String::class.java).invoke(serviceManager, Context.WINDOW_SERVICE) as IBinder
        val stub = Class.forName("android.view.IWindowManager\$Stub")
        return stub.getMethod("asInterface", IBinder::class.java).invoke(stub, serviceBinder)
    }

    fun setOverscanMode(v1: Int, v2: Int, v3: Int, v4: Int): Boolean {
        try {

            val windowManagerService = getWindowManagerService()
            for (m in windowManagerService.javaClass.methods) {
                L.d { "Method: $m" }
            }
            val setOverscan = windowManagerService.javaClass.getMethod("setOverscan", Integer.TYPE, Integer.TYPE, Integer.TYPE, Integer.TYPE, Integer.TYPE)
            setOverscan.invoke(windowManagerService, 0, v1, v2, v3, v4)
            return true
        } catch (e: Exception) {
            L.e(e)
            return false
        }

    }

    fun hasNavigationBar(): Boolean? {
        try {
            val windowManagerService = getWindowManagerService()
            val hasNavigationBar = windowManagerService.javaClass.getMethod("hasNavigationBar")
            val res = hasNavigationBar.invoke(windowManagerService) as Boolean
            L.d { "hasNavigationBar: $res" }
            return res
        } catch (e: Exception) {
            L.e(e)
            return null
        }

    }
}

Answer 1

The code here let's me believe, that there should be a setOverscan method inside the IWindowManager$Stub but there isn't. Am I doing something wrong or is it just not possible to do what I want to do the way I try to do it?

Calling getMethod won't work in this case. See the following code to get and invoke the setOverscan method:

object WindowManagerHackery {

    @SuppressLint("PrivateApi")
    @Throws(OverscanInvocationError::class)
    fun setOverscan(displayId: Int = Display.DEFAULT_DISPLAY, left: Int = 0, top: Int = 0, right: Int = 0, bottom: Int = 0) {
        try {
            val ServiceManager = Class.forName("android.os.ServiceManager")
            val service = ServiceManager.getMethod("getService", String::class.java)
            val binder = service.invoke(null, "window") as IBinder
            val windowManagerStub = Class.forName("android.view.IWindowManager").classes[0]
            val serviceObj = windowManagerStub.getMethod("asInterface", IBinder::class.java).invoke(null, binder)
            windowManagerStub.methods.first { it.name == "setOverscan" }
                    .invoke(serviceObj, displayId, left, top, right, bottom)
        } catch (e: Exception) {
            throw OverscanInvocationError(e)
        }
    }

    class OverscanInvocationError(e: Exception) : Exception(e)

}

Usage:

WindowManagerHackery.setOverscan(bottom = overscanOffset)

You will need android.permission.WRITE_SECURE_SETTINGS. I would also check out https://github.com/tiann/FreeReflection for support on API 28 but I'm not sure if Google Play has a policy against including this library in an APK if you plan on publishing on the market.