如何制作,以便用户无法删除预装的Android应用？

<uses-permission android:name="android.permission.DELETE_PACKAGES" />
<uses-permission android:name="android.permission.WRITE_SECURE_SETTINGS" />

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

<?xml version="1.0" encoding="utf-8"?><device-admin>
    <uses-policies>
       <force-lock />
       <disable-keyguard-features />
    </uses-policies>
</device-admin>

private void enableDeviceAdmin() {
    ComponentName componentName = new ComponentName(this, MyDeviceAdminReceiver.class);
    Intent intent = new Intent(DevicePolicyManager.ACTION_ADD_DEVICE_ADMIN);
    intent.putExtra(DevicePolicyManager.EXTRA_DEVICE_ADMIN, componentName);
    startActivityForResult(intent, 1);
}

@Override
public CharSequence onDisableRequested(Context context, Intent intent) {
    return "This app cannot be disabled.";
}