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Control 3G interface with your own application in Android

Filed under Guides

It is well known that we can use our application code to manipulate the WiFi interface (e.g, shutdown, bring up) with the WifiManager Service. For example:

   WifiManager wifiManager = (WifiManager) getSystemService(WIFI_SERVICE);
   wifiManager.setWifiEnabled(True | False);

But manipulating the 3G interface is much harder.  There is no a explicit guide in Android’s developer documentation, and the only method I found is not supported through the standard SDK.

I looked up the source code of Android’s Settings application, in particular Menu –> Setting –> Wireless & networks –> Mobile networks –> Data enabled.

I found that it is implemented by calling ConnectivityManager.setMobileDataEnabled function.  But this function has two problems for normal applications:

1. In the ConnectivityManager implementation, the setMobileDataEnabled is tagged hidden, which means that normal application can not trigger this function.
2. The application needs the system privilege to execute the function. Otherwise, it throws a permission error.

I will demonstrate how to solve these problems to let your code manipulate the 3G interface.

Problem 1: we can use Java reflection method to look the function in the class instance. The code is as follows:

private void setMobileDataEnabled(boolean enable) {
ConnectivityManager cm =
    (ConnectivityManager) context
          .getSystemService(Activity.CONNECTIVITY_SERVICE);
Method m = getMethodFromClass(cm, "setMobileDataEnabled");
runMethodofClass(cm, m, enable);
}

private Method getMethodFromClass(Object obj, String methodName) {
    final String TAG = "getMethodFromClass";
    Class<?> whichClass = null;
    try {
        whichClass = Class.forName(obj.getClass().getName());
     } catch (ClassNotFoundException e2) {
         Log.d(TAG, "class not found");
     }
     Method method = null;
     try {
        //method = whichClass.getDeclaredMethod(methodName);
        Method[] methods = whichClass.getDeclaredMethods();
        for (Method m : methods) {
            if (m.getName().contains(methodName)) {
                method = m;
            }
        }
     } catch (SecurityException e2) {
       Log.d(TAG, "SecurityException for " + methodName);
      }
      return method;
}

private Object runMethodofClass(Object obj, Method method, Object... argv) {
    Object result = null;
    if (method == null) return result;
    method.setAccessible(true);
    try {
       result = method.invoke(obj, argv);
    } catch (IllegalArgumentException e) {
         Log.d(TAG, "IllegalArgumentException for " + method.getName());
    } catch (IllegalAccessException e) {
         Log.d(TAG, "IllegalAccessException for " + method.getName());
    } catch (InvocationTargetException e) {
          Log.d(TAG, "InvocationTargetException for " + method.getName()
            + "; Reason: " + e.getLocalizedMessage());
    }
   return result;
}

Problem2: Add “android:sharedUserId=”android.uid.system” into the <manifest > of the project’s AndroidManifest.xml file.  Then compile the application against the Android source code tree and compilation environment.

The following are steps for compiling my application (project name: InterfaceManager). My Android source code tree is in the /media/MyHardDisk/CyanogenMod directory.

# cd /media/MyHardDisk/CyanogenMod
# cp -r InterfaceManager packages/apps/
# build/environment.sh
# lunch; [and choose 32 (passion)]
# cd package/apps/InterfaceManage

Add an Andrild.mk file like:

 LOCAL_PATH := $(call my-dir)
 include $(CLEAR_VARS)
 LOCAL_SRC_FILES := $(call all-subdir-java-files)
 LOCAL_PACKAGE_NAME := InterfaceManager
 LOCAL_CERTIFICATE := platform
 include $(BUILD_PACKAGE)

Then:

# mm;

The “mm” command will compile the project. If it succeeds, it outputs the InterfaceManager.apk to the out/target/…/ directory. You can then use “adb install InterfaceManager.apk” to install the package manually.

Note:

1. if your project created previously by Eclipse, Eclipse automatically generates gen/R.java file and you need to remove the gen directory when compiling with mm since Android compiler use a global R.java for all its applications.
2. in your layout xml file, all the customized values, for example android:text = “OK”, must be defined in xml file in values directory such as android:text = “@string/ok”