Android - Why does endCall method work but answerRingingCall doesn't work?

问题

I use the following code to handle incoming calls from within a service. It works perfectly when i invode the endCall method (My phone's Android Version is ICS). But when I invoke the answerRingingCall method i get an exception for not having permission to modify phone state. I know that Google revoked this permission at one point but since i can invoke the end call method what is the explanation for not being able to invoke the answer call method as well? I mean..both methods modify the phone's state, so what's up? Is there a way to fix this?

   try {
        TelephonyManager tm = (TelephonyManager)getBaseContext().getSystemService(Context.TELEPHONY_SERVICE);
        Class c = Class.forName(tm.getClass().getName());
        Method m = c.getDeclaredMethod("getITelephony");
        m.setAccessible(true);
        Object telephonyService = m.invoke(tm); // Get the internal ITelephony object
        c = Class.forName(telephonyService.getClass().getName()); // Get its class
        m = c.getDeclaredMethod("endCall"); // Get the "endCall()" method
        m.setAccessible(true); // Make it accessible
        m.invoke(telephonyService); // invoke endCall()
    }
    catch (Exception e) {
        Log.w("exception",e);
    }

回答1:

If I had to guess, I'd say in your OEM version of com.android.phone.PhoneInterfaceManager inside the Phone.apk the endCall function doesn't call enforceCallPermission(); before sending the request to end the call.

Where as in the answerRingingCall function calls enforceCallPermission();

You could try a hack where you get access the the private method, on the ITelephony object, sendRequestAsync set accessible to true, and then call it with 4 as the input param, aka CMD_ANSWER_RINGING_CALL.

This would avoid the permissions check.

来源：https://stackoverflow.com/questions/21584372/android-why-does-endcall-method-work-but-answerringingcall-doesnt-work