Develop Reference

How to leave the current app and launch an activity of another app?

I have a simple Android app that needs to launch another app under certain condition, and I will need to check the condition upon the app launch. That is, either continue to launch my app or just launch another app:
if (A == true) {
launch another activity of another app
leave the current app without creating the main activity
} else {
launch the main activity of the current app
}
Could anyone please let me know how to deal with A == true case? I am able to launch another app's activity but I have trouble leaving the current app without even opening the main activity.
Any help will be greatly appreciated!

You can launch other application using following intent
Intent LaunchIntent = getPackageManager().getLaunchIntentForPackage("com.example.abc");//pass the packagename of app you want to open
startActivity( LaunchIntent );
If you don't know the package name of application that you wanted to launch then try your hand on
PackageManager pm;
pm = getPackageManager();
// get a list of installed apps.
packages = pm.getInstalledApplications(0);
Pass the packagename of app you want to open
You can use this if A == true
else You can launch the MainActivity as
startActivity(new Intent(CurrentActivity.this,MainActivity.class));

If you want to start another activity of another app without the normal IntentFilter then the easiest solutions is:
Intent intent = new Intent(Intent.ACTION_MAIN);
intent.setComponent(new ComponentName("com.anotherapp.package","com.anotherapp.package.MainActivity"));
startActivity(intent);
Of course, you would need to know the package name and the Activity name you want to start
As for finishing your application call
finishAndRemoveTask();

Launch an activity of an application from a different application on Android

I need to launch an activity (not the main activity) of an application from an application I have made. The activity I want to launch is proprietary, hence, I cannot make any changes to its code(or manifest).
For example: I want to launch somebody's Facebook profile from my own application. A normal intent to facebook from my app would open the 'newsfeed'(which I don't want). I want to know how to access any other activity.
Thanks in advance!
The little code I have:
String PACKAGE="com.facebook.katana";
Intent launchIntent = getPackageManager()
.getLaunchIntentForPackage(PACKAGE);
startActivity(launchIntent);

To launch specific activity you need to use explicit intent. Or use implicit intent with action if you know what action that activity answers to.
To use explicit intent you can do the following (provided you call it from the activity):
Intent intent = new Intent();
intent.setComponent(new ComponentName("com.package.name", "com.package.name.ActivityName"));
if(getPackageManager().resolveActivity(intent, 0) != null) {
startActivity(intent);
} else {
Toast.makeText(this, "No app installed that can perform this action", Toast.LENGTH_SHORT).show();
}
You can also add flags to the intent, add actions and categories. As long as the intent can be resolved as viable intent by the PackageManager, it will launch the activity.
Now...
The question about facebook profile, is a different one.
Perhaps, the best way to achieve that would be to use intent with action VIEW and povide Intent.setData with uri to the profile page. That should also be checked for possibility of being resolved correctly. And then will launch the chooser of all supported activities to open it, which should include facebook application. It is then up to user to open the intent using Facebook app or launcher.

dont allow to Open own application from another app

I have seen some of example where other application can start my application by package name. Due to security reason I want to prevent this kind of access for other application.
I want to prevent this (Open another application from your own (intent)) kind of acess
Edit
For Example, If thirdparty application knows my application's package name they can launch my app from their application like this way,
Intent i;
PackageManager manager = getPackageManager();
try {
i = manager.getLaunchIntentForPackage("app package name");
if (i == null)
throw new PackageManager.NameNotFoundException();
i.addCategory(Intent.CATEGORY_LAUNCHER);
startActivity(i);
} catch (PackageManager.NameNotFoundException e) {
}
Now to prevent this, i have added export = "false" in my launching activity as well as added permission to lauching activity. Now due to this, it is preventing thirdparty app to launch my application but android OS launcher is also not able to launch application.

I imagine if you don't provide the launch intent in your Android manifest, other apps (including your homescreen) won't be able to launch your app.

You can try these attributes in manifest:
http://developer.android.com/guide/topics/manifest/activity-element.html#exported
http://developer.android.com/guide/topics/manifest/service-element.html#exported
http://developer.android.com/guide/topics/manifest/receiver-element.html#exported
http://developer.android.com/guide/topics/manifest/provider-element.html#exported
As also mentioned in those links, you can try another approach by using permission with the protectionLevel = signature
http://developer.android.com/guide/topics/manifest/permission-element.html#plevel

I hope below solution by comparing package name will help you protecting your activity to be launched by other app.
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ComponentName componentName = this.getCallingActivity();
if(componentName == null) {
finish();
} else if("<intended package name>".equals(componentName.getPackageName())) {
finish();
} else {
String data = getIntent().getDataString();
...
}
}
}
Above solution is base on below assumption:
Only one app with a particular package name can exist on Google Play.
If a user tries to install an app whose package name already exists on the device, the installation either will fail or will overwrite the previously installed app.

When is a Home not a Home (Launcher related)

I am running into a very strange situation whereby I am getting a list of all the installed packages that have a CATEGORY_HOME intent.
My intention is to manually launch the native Home application (which is currently NOT the Default native Home application, because my application has that role).
So, the method I'm using (beneath) correctly identifies that there are two apps that are set up as CATEGORY_HOME.
When I try to launch the one that is mine (fetching the Launcher activity) it works fine. However, when I try to fetch the Launcher activity for the default one, it comes back as null.
So... I'm stumped. How do I determine what I should actually be launching when the package name of the stock home app returns null when I try and pull the relevant Launch activity via getLaunchIntentForPackag from it?
Here's what I'm doing (with some comments to avoid confusion), and for the record I know that not all of them will have the expression "android" in the name space, but I'm trying to get this to work initially on a device that does come back with that string so that part of it isn't the issue.
//get a list of all apps that set themselves up as CATEGORY_HOME
final Intent intent = new Intent(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_HOME);
final List<ResolveInfo> list = ((PackageManager)getPackageManager()).queryIntentActivities(intent, 0);
String packageName = null;
//look for the one that has the word android in the package name
for(ResolveInfo ri : list){
if(ri.activityInfo.packageName.indexOf("android") != -1)
//this does get set correctly and looks like "com.sec.android.app.launcher"
packageName = ri.activityInfo.packageName;
}
PackageManager pm = SlidePlayer.this
.getPackageManager();
Intent it = pm.getLaunchIntentForPackage(packageName);
//it is NULL so this doesn't work
startActivity(it);
***EDIT
Trying out the following methodology based on CommonsWare's advice...
String packageName = null;
String className = null;
for(ResolveInfo ri : list){
//L.d("HOME PACK = " + ri.);
if(ri.activityInfo.packageName.indexOf("android") != -1){
className = ri.activityInfo.applicationInfo.className;
packageName = ri.activityInfo.applicationInfo.packageName;
}
}
//PackageManager pm = SlidePlayer.this
//.getPackageManager();
Intent it = new Intent();//pm.getLaunchIntentForPackage(packageName);
//both packageName and className appear to be set correctly
//packageName = "com.sec.android.app.launcher"
//className = "com.android.launcher2.LauncherApplication"
it.setClassName(packageName, className);
it.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(it);
EDIT 2*
semi huzzah...
On one device (Samsung Note II) the key is to set it via Component like so...
Intent it = new Intent();//pm.getLaunchIntentForPackage(packageName);
ComponentName cn = new ComponentName(packageName, className);
it.setComponent(cn);
//it.setClassName(packageName, className);
it.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(it);
This doesn't work on the Samsung Tab 10" or the Motorola M (which are the only other 2 devices I have thus far tested with this methodology).

getLaucnIntentForPackage looks specifically for CATEGORY_INFO or CATEGORY_LAUNCHER - not CATEGORY_HOME, in which case it will return null. From the Documentation:
public abstract Intent getLaunchIntentForPackage (String packageName)
Added in API level 3 Return a "good" intent to launch a front-door
activity in a package, for use for example to implement an "open"
button when browsing through packages. The current implementation will
look first for a main activity in the category CATEGORY_INFO, next for
a main activity in the category CATEGORY_LAUNCHER, or return null if
neither are found.

However, when I try to fetch the Launcher activity for the default one, it comes back as null.
That's because most firmware home screens are not designed to be launched by home screens, and so probably do not include a launcher activity.
How do I determine what I should actually be launching when the package name of the stock home app returns null when I try and pull the relevant Launch activity via getLaunchIntentForPackag from it?
Since it is a home screen, you know that it must have an activity with the same ACTION_MAIN/CATEGORY_HOME as you do. Find that one and start it.

open android own launcher from my application

hi Its been 2 days looking for this simple problem. I want to launch Android own launcher from my application EVEN if its not set as default.
final PackageManager packageManager=getPackageManager();
Intent intent = packageManager.getLaunchIntentForPackage("com.android.launcher");
this return null for Android own launcher but if I try custom launcher is give me successfully

Found the solution, after investigating source code of getLaunchIntentForPackage. As per documentation,
The current implementation will look first for a main activity in the
category CATEGORY_INFO, next for a main activity in the category
CATEGORY_LAUNCHER, or return null if neither are found.
So, the function don't look for CATEGORY_HOME, i rewrote it in following way, it worked perfectly.
Intent intentToResolve = new Intent(Intent.ACTION_MAIN);
intentToResolve.addCategory(Intent.CATEGORY_HOME);
intentToResolve.setPackage("com.android.launcher");
ResolveInfo ri = getPackageManager().resolveActivity(intentToResolve, 0);
if (ri != null)
{
Intent intent = new Intent(intentToResolve);
intent.setClassName(ri.activityInfo.applicationInfo.packageName, ri.activityInfo.name);
intent.setAction(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_HOME);
startActivity(intent);
}

Are you sure the default Google Android Launcher being installed on your device? If not, then it's truly NULL.