Develop Reference

What is the proper way to implement SharedPreferencesBackupHelper?

initial use of sharedpreferences.
BackupManager bm = new BackupManager(getApplicationContext());
SharedPreferences sharedPreferences = getSharedPreferences("AppData", MODE_PRIVATE);
if(sharedPreferences.getBoolean("my_first_time", true)) {
sharedPreferences.edit().putBoolean("my_first_time", false).apply();
sharedPreferences.edit().putString("user_id", String.valueOf(dbh.insertUserId())).apply();
sharedPreferences.edit().putInt("noteIndex", -1).apply();
sharedPreferences.edit().putInt("checklistIndex", -1).apply();
bm.dataChanged();
}
Backing up data
public class MyPrfsBackupAgent extends BackupAgentHelper {
#Override
public void onCreate() {
SharedPreferencesBackupHelper helper = new SharedPreferencesBackupHelper(this, "AppData");
addHelper("sharedprefs_key", helper);
}
}
My goal is to backup the whole sharedpreferences file 'AppData' and restore it after re-installation of the feature is failing to complete its task. Ive tried it with allowbackup in manifest on both true and false, and running it on my actual device to test it but nothing seems to work accordingly.
items added to AndroidManifest.xml in attempt to fix this
android:backupAgent=".BackupData$MyPrfsBackupAgent"
<meta-data android:name="com.google.android.backup.api_key"
android:value="value" />
I followed the docs on this as well as other stackoverflow references but none have helped me solve the problem. I would be open to trying a different way of backup/restoring but cant find another and wont use autoBackup because it targets sdk 23 while my min is 21.

All the shared preferences data is stored in shared preferences .xml files in getFilesDir().getParentFile() directory in a folder named shared_prefs.
Simply copy all the files there to any place you want.
At reinstall do the reverse and reboot.

How to implement Android’s Data Backup Service

For my Android Project I tried to follow and implement Android Developers Data Backup Guidelines ( http://developer.android.com/guide/topics/data/backup.html ), but Data Backup and Restore doesn't work. Can someone help with examples?

With further investigation I figured out the steps to implement Android Data Backup and Restore. They are:
Add in Manifest xml file the following:
a. android:allowBackup="true" (This enables Android’s Data Backup Service)
b. meta-data android:name="com.google.android.backup.api_key"
android:value=”{Your unique Registration Key for Android Backup Service}” (You must register your application package name with a backup service. To generate a key, go to http://developer.android.com/google/backup/signup.html )
c. android:backupAgent=”.MyBackupAgent” (This is the name of class that implement’s your declared backup agent class). Note1: The first character of the name is a period for the purpose of a shorthand to locate your “com.example.project.MyBackupAgent”. Note2: If a run time Exception occurs (this may or may not happen depending on your project stucture) such as: java.lang.ClassNotFoundException: Didn’t find class “com.example.project.MyBackupAgent” then I suggest you Decompile your apk (Upload your apk package in http://www.decompileandroid.com/ ) and search for the absolute path to your MyBackupAgent and insert this path for android:backupAgent=”{absolute path}.MyBackupAgent”
Here’s an example of a Manifest xml file with Backup support:
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.project">
<application android:allowBackup="true" android:backupAgent="md5f576d3976d691fac04b078d1718cab3.MyBackupAgent">
<meta-data android:name="com.google.android.backup.api_key" >android:value="{Your unique Registration Key}" />
</application>
Add in project your MyBackupAgent class. The BackupAgentHelper class provides a convenient wrapper around the BackupAgent class, which minimizes the amount of code you need to write. In your BackupAgentHelper, you must use one or more "helper" objects, which automatically backup and restore certain types of data, so that you do not need to implement onBackup() and onRestore().
Note: Android currently provides backup helpers that will backup and restore complete files from SharedPreferences and internal storage.
Here’s a Java SharedPreferenceBackupHelper example for MyBackupAgent class:
import android.app.backup.BackupAgentHelper;
import android.app.backup.SharedPreferencesBackupHelper;
import android.util.Log;
public class MyBackupAgent extends BackupAgentHelper{
static final String PREFS = "myprefs";
static final String PREFS_BACKUP_KEY = "myprefs";
#Override
public void onCreate() {
Log.i("MyFileBackupAgent", "****** Enter BACKUP CLASS *******");
SharedPreferencesBackupHelper helper = new SharedPreferencesBackupHelper(this, PREFS);
addHelper(PREFS_BACKUP_KEY, helper);
Log.i("MyFileBackupAgent", "****** Exit BACKUP CLASS ********");
}
}
Here’s a C# Xamarin FileBackupHelper example for MyBackupAgent class:
public class MyBackupAgent: BackupAgentHelper
{
string myProtectData = "File.bin";
string myPersistentData = "Data.bin";
string myDBase = "Database.db";
public override void OnCreate()
{
Console.WriteLine ("****** Enter Backup Files Helpers *********");
base.OnCreate ();
try
{
FileBackupHelper dbkh = new FileBackupHelper (this, myProtectData);
this.AddHelper ("PROTECT_backup", dbkh);
FileBackupHelper persisth = new FileBackupHelper (this, myPersistentData);
this.AddHelper ("PERSIST_backup", persisth);
FileBackupHelper dbh = new FileBackupHelper (this, myDBase);
this.AddHelper ("DATABASE_backup", dbh);
Console.WriteLine ("********* All 3 files backuped *********");
}
catch {
Console.WriteLine ("******* Backup AddHelper Exception ERROR *********");
}
Console.WriteLine ("******** Exit Backup Files Helpers ********");
}
public override void OnBackup(ParcelFileDescriptor oldState, BackupDataOutput data, ParcelFileDescriptor newState)
{
Console.WriteLine ("****** Override OnBackup called ******");
base.OnBackup(oldState, data, newState);
}
public override void OnRestore (BackupDataInput data, int appVersionCode, ParcelFileDescriptor newState)
{
Console.WriteLine ("****** Override OnRestore called ******");
base.OnRestore(data, appVersionCode, newState);
}
}
To perform a backup, your code should make a backup request by calling the dataChanged(). A backup request does not result in an immediate call to your onBackup() method. Instead, the Backup Manager waits for an appropriate time*, then performs backup for all applications that have requested a backup since the last backup was performed. Note, The Backup Manager Service responds every hour as long as at least one DataChanged() was called in-between the hour since the last data backup request.
For test purposes, an immediate backup can be performed with the Android SDK Command Prompt Tool. Try these commands:
To ensure Data Backup Enabled:
adb shell bmgr enable true
To request a Data Backup:
adb shell bmgr backup
To initiate a Data Backup:
adb shell bmgr run
To uninstall your App:
adb uninstall
Then install your App:
adb install
What about your phone device Backup settings? Make sure a WiFi connection is established. Also, under device Settings, make sure "Back up my data" and "Automatic restore" are checked and you have entered in a valid Backup Account email id.
Lastly, to track your Backup upload time stamps, use www.google.com/settings/dashboard (this is your personal google account that matches your google account in your Android phone device Backup settings)

Clear parse installation cache on Android

does anyone know how to clear the data from the parse installation on the newer library version 1.10? In 1.8 you could do it via reflection by calling clear from memory, like described in this answer: ParseObject mergeREST raise ConcurrentModificationException
I am deleting the parse installation from web, and I also need to clear the ram cache on the android phone and I can't find a way to do it. Any ideas?

Solved by making a package in my project named com.parse, in it I've placed a file named ParseEasyAccess.java , it contains the following method:
public static void clearParse() {
ParseInstallation.getCurrentInstallationController().clearFromDisk();
ParseInstallation.getCurrentInstallationController().clearFromMemory();
}
You can call this from anywhere in the app and it will clear all the parse installation data from RAM & disk.

The accepted answer will not work for sdk version 1.13.1.
The only way to access those methods is like this:
ParseInstallation installation = ParseInstallation.getCurrentInstallation();
Class clazz = installation.getClass();
Method[] methods = clazz.getDeclaredMethods();
Method method1 = clazz.getDeclaredMethod("getCurrentInstallationController");
method1.setAccessible(true);
Object result = method1.invoke(installation);
Method method2 = result.getClass().getDeclaredMethod("clearFromDisk");
method2.setAccessible(true);
String result2=(String) method2.invoke(result);
Method method3 = result.getClass().getDeclaredMethod("clearFromMemory");
method3.setAccessible(true);
String result3=(String) method3.invoke(result);

Android Backup of Shared Preferences to Google Backup Service not working

I've researched and followed how to get my android app to backup the data to google backup so if user loses phone or upgrades to a new phone, they don't lose their data. However, when I test it out (by using the app myself, then uninstalling and reinstalling), no data is restored. Here's what I've done. Perhaps someone can figure out what is wrong.
Applied for a backup key from google
Placed following code in Manifest File (in place of key I did add the key value and for packageName I used my app package name)
android:backupAgent="packageName.MyPrefsBackup">
<meta-data android:name="com.google.android.backup.api_key" android:value="key" />
Created class MyPrefsBackup with following code. The name of the sharedpreference file I want to backup is called UserDB. As far as the PREFS_BACKIP_KEY, I just called it prefs. From what I understand, this is not the same key as the one that goes in the manifest file.
Code:
package packageName;
import android.app.backup.BackupAgentHelper;
import android.app.backup.SharedPreferencesBackupHelper;
public class MyPrefsBackup extends BackupAgentHelper {
// The name of the SharedPreferences file
static final String PREFS = "UserDB";
// A key to uniquely identify the set of backup data
static final String PREFS_BACKUP_KEY = "prefs";
// Allocate a helper and add it to the backup agent
public void onCreate() {
SharedPreferencesBackupHelper helper = new SharedPreferencesBackupHelper(this, PREFS);
addHelper(PREFS_BACKUP_KEY, helper);
}
}
Added BackupManager mBackupManager = new BackupManager(this); in my main class where I call the backup manager in next step
Lastly, in my main program I call the backupHelper when data is changed by the following line:
mBackupManager.dataChanged();
Any help is much appreciated.

try new BackupManager(this).dataChanged()

If you are testing this from AVD - you'll need to enable backups - AVD are disabled for backups by default.
adb shell bmgr enable true
Then you can actually debug it to see if the onCreate is called after running
adb shell bmgr run

Is it possible to dynamically load a library at runtime from an Android application?

Is there any way to make an Android application to download and use a Java library at runtime?
Here is an example:
Imagine that the application needs to make some calculations depending on the input values. The application asks for these input values and then checks if the required Classes or Methods are available.
If not, it connects to a server, downloads the needed library, and loads it at runtime to calls the required methods using reflection techniques. The implementation could change depending on various criteria such as the user who is downloading the library.

Sorry, I'm late and the question has already an accepted answer, but yes, you can download and execute external libraries. Here is the way I did:
I was wondering whether this was feasible so I wrote the following class:
package org.shlublu.android.sandbox;
import android.util.Log;
public class MyClass {
public MyClass() {
Log.d(MyClass.class.getName(), "MyClass: constructor called.");
}
public void doSomething() {
Log.d(MyClass.class.getName(), "MyClass: doSomething() called.");
}
}
And I packaged it in a DEX file that I saved on my device's SD card as /sdcard/shlublu.jar.
Then I wrote the "stupid program" below, after having removed MyClass from my Eclipse project and cleaned it:
public class Main extends Activity {
#SuppressWarnings("unchecked")
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
try {
final String libPath = Environment.getExternalStorageDirectory() + "/shlublu.jar";
final File tmpDir = getDir("dex", 0);
final DexClassLoader classloader = new DexClassLoader(libPath, tmpDir.getAbsolutePath(), null, this.getClass().getClassLoader());
final Class<Object> classToLoad = (Class<Object>) classloader.loadClass("org.shlublu.android.sandbox.MyClass");
final Object myInstance = classToLoad.newInstance();
final Method doSomething = classToLoad.getMethod("doSomething");
doSomething.invoke(myInstance);
} catch (Exception e) {
e.printStackTrace();
}
}
}
It basically loads the class MyClass that way:
create a DexClassLoader
use it to extract the class MyClass from "/sdcard/shlublu.jar"
and store this class to the application's "dex" private directory (internal storage of the phone).
Then, it creates an instance of MyClass and invokes doSomething() on the created instance.
And it works... I see the traces defined in MyClass in my LogCat:
I've tried on both an emulator 2.1 and on my physical HTC cellphone (which is running Android 2.2 and which is NOT rooted).
This means you can create external DEX files for the application to download and execute them. Here it was made the hard way (ugly Object casts, Method.invoke() ugly calls...), but it must be possible to play with Interfaces to make something cleaner.
Wow. I'm the first surprised. I was expecting a SecurityException.
Some facts to help investigating more:
My DEX shlublu.jar was signed, but not my app
My app was executed from Eclipse / USB connection. So this is an unsigned APK compiled in DEBUG mode

Shlublu's anwser is really nice. Some small things though that would help a beginner:
for library file "MyClass" make a separate Android Application project which has the MyClass file as only file in the src folder (other stuff, like project.properties, manifest, res, etc. should also be there)
in library project manifest make sure you have:
<application android:icon="#drawable/icon"
android:label="#string/app_name">
<activity android:name=".NotExecutable"
android:label="#string/app_name">
</activity>
</application>
(".NotExecutable" is not a reserved word. It is just that I had to put something here)
For making the .dex file, just run the library project as android application (for the compiling) and locate .apk file from the bin folder of the project.
Copy the .apk file to your phone and rename it as shlublu.jar file (an APK is actually a specialization of a jar, though)
Other steps are the same as described by Shlublu.
Big thanks to Shlublu for cooperation.

Technically should work but what about Google rules?
From: play.google.com/intl/en-GB/about/developer-content-policy-pr‌​int
An app distributed via Google Play may not modify, replace or update
itself using any method other than Google Play’s update mechanism.
Likewise, an app may not download executable code (e.g. dex, JAR, .so
files) from a source other than Google Play. This restriction does not
apply to code that runs in a virtual machine and has limited access to
Android APIs (such as JavaScript in a WebView or browser).

I am not sure if you can achieve this by dynamically loading java code. May be you can try embedding a script engine your code like rhino which can execute java scripts which can be dynamically downloaded and updated.

sure, it is possible. apk which is not installed can be invoked by host android application.generally,resolve resource and activity's lifecircle,then,can load jar or apk dynamically.
detail,please refer to my open source research on github: https://github.com/singwhatiwanna/dynamic-load-apk/blob/master/README-en.md
also,DexClassLoader and reflection is needed, now look at some key code:
/**
* Load a apk. Before start a plugin Activity, we should do this first.<br/>
* NOTE : will only be called by host apk.
* #param dexPath
*/
public DLPluginPackage loadApk(String dexPath) {
// when loadApk is called by host apk, we assume that plugin is invoked by host.
mFrom = DLConstants.FROM_EXTERNAL;
PackageInfo packageInfo = mContext.getPackageManager().
getPackageArchiveInfo(dexPath, PackageManager.GET_ACTIVITIES);
if (packageInfo == null)
return null;
final String packageName = packageInfo.packageName;
DLPluginPackage pluginPackage = mPackagesHolder.get(packageName);
if (pluginPackage == null) {
DexClassLoader dexClassLoader = createDexClassLoader(dexPath);
AssetManager assetManager = createAssetManager(dexPath);
Resources resources = createResources(assetManager);
pluginPackage = new DLPluginPackage(packageName, dexPath, dexClassLoader, assetManager,
resources, packageInfo);
mPackagesHolder.put(packageName, pluginPackage);
}
return pluginPackage;
}
your demands is only partly of function in the open source project mentioned at the begining.

If you're keeping your .DEX files in external memory on the phone, such as the SD card (not recommended! Any app with the same permissions can easily overwrite your class and perform a code injection attack) make sure you've given the app permission to read external memory. The exception that gets thrown if this is the case is 'ClassNotFound' which is quite misleading, put something like the following in your manifest (consult Google for most up to date version).
<manifest ...>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"
android:maxSdkVersion="18" />
...
</manifest>

I think #Shlublu answer is correct but i just want to highlight some key points.
We can load any classes from external jar and apk file.
In Any way, we can load Activity from external jar but we can not start it because of the context concept.
To load the UI from external jar we can use fragment. Create the instance of the fragment and embedded it in the Activity. But make sure fragment creates the UI dynamically
as given below.
public class MyFragment extends Fragment {
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup
container, #Nullable Bundle savedInstanceState)
{
super.onCreateView(inflater, container, savedInstanceState);
LinearLayout layout = new LinearLayout(getActivity());
layout.setLayoutParams(new
LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT,
LinearLayout.LayoutParams.MATCH_PARENT));
Button button = new Button(getActivity());
button.setText("Invoke host method");
layout.addView(button, LinearLayout.LayoutParams.MATCH_PARENT,
LinearLayout.LayoutParams.WRAP_CONTENT);
return layout;
}
}