No active admin owned … - locking a screen in Android

Question

I want to simply lock the screen. Here's what I did:

public class MainActivity : ActionBarActivity() {
    var dpm: DevicePolicyManager? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        dpm = getSystemService(Context.DEVICE_POLICY_SERVICE) as DevicePolicyManager
    }

    override fun onCreateOptionsMenu(menu: Menu?): Boolean {
        getMenuInflater()?.inflate(R.menu.menu_main, menu)
        dpm?.lockNow()
        return true
    }
}

It's in Kotlin but those who Java will understand it.

And manifest:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="android.me.com.app123" >
    <uses-permission
        android:name="android.permission.USES_POLICY_FORCE_LOCK">
    </uses-permission>

    <application
        android:allowBackup="true"

The error is:

android.me.com.app123 E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: android.me.com.app123, PID: 22964
    java.lang.SecurityException: No active admin owned by uid 10121 for policy #3
            at android.os.Parcel.readException(Parcel.java:1472)

Haven't I gotten enough permissions when I said "android.permission.USES_POLICY_FORCE_LOCK"? If not how to fix it?

Answer 1

In order to be able to lock the screen, you need to add a Device Admin as described here .

Second: If you got any properties, which you cant assign a value in the constructor, use the notNull-Delegate.

var dpm: DevicePolicyManager by Delegates.notNull()

When you access dpm before it is set, a NPE is thrown. If not, you wont have to check dpm for null all the time.

Answer 2

(previous answer links the correct tutorial)

Your received error because your app not enabled as Device Admin.

Key points for the (pof) implementation:

Policy definition resource (res/xml/....):

<device-admin>
    <uses-policies>
        <force-lock />
    </uses-policies>
</device-admin>

Broadcast receiver:

<receiver android:name="your.LockDeviceAdminReceiver" 
        android:permission="android.permission.BIND_DEVICE_ADMIN">
    <meta-data android:name="android.app.device_admin"
        android:resource="@xml/device_admin" />
    <intent-filter>
        <action android:name="android.app.action.DEVICE_ADMIN_ENABLED" />
    </intent-filter>
</receiver>

Check enabled state of your Admin (and start activity if not and handle the result):

val devicePolicyManager = getSystemService(Context.DEVICE_POLICY_SERVICE) 
    as DevicePolicyManager
val deviceAdminReceiver = ComponentName(context, 
    LockDeviceAdminReceiver::class.java)

if (devicePolicyManager.isAdminActive(deviceAdminReceiver)) {
   devicePolicyManager.lockNow()
} else {
    val intent = Intent(DevicePolicyManager.ACTION_ADD_DEVICE_ADMIN)
    intent.putExtra(DevicePolicyManager.EXTRA_DEVICE_ADMIN, 
        deviceAdminReceiver))
    startActivityForResult(intent, ENABLE_ADMIN_REQUEST_CODE);
}

Answer 3

You would need 3 thing to do :

1. add <receiver> to AndroidManifest
2. make new xml file for <device-admin>
3. make new .kt file for DeviceAdminReceiver

Here is an answer I already did (with code in Kotlin) : stackoverflow.com