Develop Reference

How to run activity from 3rd party library?

I am in a non-activity class. In this place I want to run the activity from a 3rd party library which I attached to my project. I have written some code which I thought will do it:
Intent intent = new Intent();
intent.putExtra(THIRD_PARTY_ACTIVITY.REPORT_EXTRA, parts.toString());
Activity activity = new THIRD_PARTY_ACTIVITY();
activity.startActivity(intent);
This code compiles successful but when I execute it, I get the error:
Caused by: java.lang.NullPointerException: Attempt to invoke virtual
method 'android.app.ActivityThread$ApplicationThread
android.app.ActivityThread.getApplicationThread()' on a null object
reference
How can I run activity from a 3rd party library?

You're doing it wrong. You NEVER create an Activity with new. It won't initialize correctly. Instead, you create an Intent to launch that Activity and call context.startActivity() to create and launch it.
void launchThirdPartyActivity(Context context) {
Intent intent = new Intent(context, THIRD_PARTY_ACTIVITY.class);
context.startActivity(intent);
}
That should work if the activity is in a library. If you're trying to launch an Activity in another app on the device, you'd use one of the other Intent constructors (which one depends on how/what you're trying to launch- a specific activity in a specific app? An activity that can perform an action (like share or view) on a specific data type? Something else?)

In your library you can do this:
Intent intent = new Intent();
// Here you need to set the ACTION or the COMPONENT in the Intent
// so that Android knows which Activity you want to start
// Also, you need to set FLAG_ACTIVITY_NEW_TASK because you aren't calling
// startActivity() on an Activity Context
intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
intent.putExtra(THIRD_PARTY_ACTIVITY.REPORT_EXTRA, parts.toString());
Application.getApplicationContext().startActivity(intent);

Android - can't go back to mainActivity after starting a different app

Okay, I think I'm missing something here but can't seem to find a way around it :\
So this is my scenario, I have two apps, A and B. A Opens a B with the following intent:
PackageManager pm = getPackageManager();
Intent n = pm.getLaunchIntentForPackage(currAppInfo.getName());
n.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(n);
(currAppInfo is a custom object and getName returns the package name.)
Anyway, B is installing APKs. A receives the package installed broadcast and should be now moved back to front, how ever if I'm starting app A with an intent
Intent serviceIntent = new Intent();
serviceIntent.setClass(context, MainActivity.class);
serviceIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
context.startActivity(serviceIntent);
Instead of seeing A's mainActivity screen all I see is B's main activity screen.
Why is that? Is it the way I open the apps with the intents or am I missing something more basic here?

Launching Activity from another App? (with AndroidAnnotations)

How can i launch an AndroidAnnotations Activity_ inside of an App (main)
since external Activity (another App).
this is my current code:
Intent codeScannerActivity = new Intent(PACKAGE, CODE_SCANNER_ACTIVITY);
codeScannerActivity.putExtra("codeScannerType", CameraUtils.CODE_SCANNER_SINGLE);
startActivityForResult(codeScannerActivity, Core.ActivityResult.RequestCode.CODE_SCANNER);
where PACKAGE = "main.app.package"
and CODE_SCANNER_ACTIVITY = PACKAGE + ".activity.MyActivity_"
but logs throws:
android.content.ActivityNotFoundException: No Activity found to handle Intent { act=main.app.package dat=main.app.package.activity.MyActivity_ (has extras) }
Activity is defined in the Manifest's Main App with the Class "etc.MyActivity_".

You are constructing the Intent incorrectly. For the constructor you are using, the first parameter is interpreted as an "action" and the second as a URI. The error says that there is no activity which can respond to the action "main.app.package" and the URI "main.app.package.activity.MyActivity_".
To fix the problem, first read Starting Another Activity and the Intent javadocs from the Android Developer site. Especially look at the documentation for the available constructors. There might be one more appropriate for your purposes than the one you are trying to use. The Intent documentation has a list of standard Activity actions. If you want to start a specific activity, you should use Intent (Context packageContext, Class<?> cls):
Intent intent = new Intent(this, main.app.package.activity.MyActivity_.class);

I was creating wrong the Intent, this is the right way:
Intent codeScannerActivity = new Intent();
codeScannerActivity.setComponent(new ComponentName(PACKAGE, CODE_SCANNER_ACTIVITY));
codeScannerActivity.putExtra("codeScannerType", CameraUtils.CODE_SCANNER_SINGLE);
startActivityForResult(codeScannerActivity, Core.ActivityResult.RequestCode.CODE_SCANNER);

Prompt for default activity without actually opening activity

I need to set the default app for a specific mime type. I know how to clear the default but I need to then prompt the user without actually opening the app.
PackageManager p = mContext.getPackageManager();
ComponentName cN = new ComponentName(mContext, FakeDownloadActivity.class);
p.setComponentEnabledSetting(cN, PackageManager.COMPONENT_ENABLED_STATE_ENABLED, PackageManager.DONT_KILL_APP);
Intent selector = new Intent(Intent.ACTION_DEFAULT);
selector.addCategory(Intent.CATEGORY_DEFAULT);
selector.setType(mimeType);
mContext.startActivity(selector);
p.setComponentEnabledSetting(cN, PackageManager.COMPONENT_ENABLED_STATE_DISABLED, PackageManager.DONT_KILL_APP);
The code above launches the activity rather than ONLY selecting the default activity. It works be enabling a fake activity then disabling it. This causes the Select Default App dialog to show the next time it is called. I simply want to ONLY select the default activity.

What you are looking for is an ACTION_PICK_ACTIVITY intent.
First, you create an intent that defines the apps that should be eligible to choose, for instance:
Intent mainIntent = new Intent(Intent.ACTION_DEFAULT, null);
mainIntent.addCategory(Intent.CATEGORY_DEFAULT);
Then, you create the ACTION_PICK_ACTIVITY intent, and as an Extra, you pass the main intent you created before
Intent pickIntent = new Intent(Intent.ACTION_PICK_ACTIVITY);
pickIntent.putExtra(Intent.EXTRA_INTENT, mainIntent);
Now, you just start an activity for result with this intent:
startActivityForResult(pickIntent, 0);
And a dialog will be created where the used can pick an application, but when clicked, the activity is not launched, instead, it will stay in your activity, and the function onActivityResult will be called with the results. So you need to create that function:
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
//In data, you have all the information about the selected application
if (data != null) {
//You can launch the application that we just picked with startActivity(data);
//or explore the variable to get all the information than you want
}
}
Take a look at the Intent class. There you have information about the package name, and the class that would be launched.
From now, what you need is to set that package and class as the default to the intent, or whatever else you need. The bad side, is that you only can save that information for your own internal purposes, for example to decide what app to launch next time that the users performs some action. What you cannot do is to modify the system settings to set a default activity for a given intent. Actually, the package manager has the addPreferredActivity method, that was supposed to do this, but it is deprecated since API level 8, giving this reasons:
This is a protected API that should not have been available to third
party applications. It is the platform's responsibility for assigning
preferred activities and this cannot be directly modified. Add a new
preferred activity mapping to the system. This will be used to
automatically select the given activity component when
Context.startActivity() finds multiple matching activities and also
matches the given filter.

Android call OEM activity by component name

On a Huwaie Ascend, when we walk through the settings menu:
Settings -> SD card & phone storage -> Software Upgrade -> SD card Upgrade
We are then brought to a screen where the user can upgrade.
And then using adb logcat we see this:
Starting activity: Intent { act=android.intent.action.MAIN cmp=com.android.settings/.SystemUpgradeCheck }
We can use adb to simulate this by calling:
adb shell am start -n com.android.settings/.SystemUpgradeCheck
This is successful, and we see the screen.
However, when we try to call this from within an activity like this:
Intent i = new Intent(Intent.ACTION_MAIN);
i.setComponent(new ComponentName("com.android.settings", ".SystemUpgradeCheck"));
startActivity(i);
We get this error:
Caused by: android.content.ActivityNotFoundException: Unable to find explicit activity class {com.android.settings/.SystemUpgradeCheck}; have you declared this activity in your AndroidManifest.xml?
What can we do to overcome this? Am I calling the intent wrong?

Figured it out :)
Context foreignContext = createPackageContext("com.android.settings", Context.CONTEXT_IGNORE_SECURITY | Context.CONTEXT_INCLUDE_CODE);
Class<?> yourClass = foreignContext.getClassLoader().loadClass("com.android.settings.SystemUpgradeCheck");
Intent intent = new Intent(foreignContext, yourClass);
startActivity(intent);