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When the screen is rotated, the current instance of activity is destroyed a new instance of the Activity is created in the new orientation. The onRestart() method is invoked first when a screen is rotated. The other lifecycle methods get invoked in the similar flow as they were when the activity was first created.
Standard: It creates a new instance of an activity in the task from which it was started. Multiple instances of the activity can be created and multiple instances can be added to the same or different tasks.
Example: Suppose there is an activity stack of A -> B -> C. Now if we launch B again with the launch mode as “standard”, the new stack will be A -> B -> C -> B.
SingleTop: It is the same as the standard, except if there is a previous instance of the activity that exists in the top of the stack, then it will not create a new instance but rather send the intent to the existing instance of the activity.
Example: Suppose there is an activity stack of A -> B. Now if we launch C with the launch mode as “singleTop”, the new stack will be A -> B -> C as usual.
Now if there is an activity stack of A -> B -> C. If we launch C again with the launch mode as “singleTop”, the new stack will still be A -> B -> C.
SingleTask: A new task will always be created and a new instance will be pushed to the task as the root one. So if the activity is already in the task, the intent will be redirected to onNewIntent() else a new instance will be created. At a time only one instance of activity will exist.
Example: Suppose there is an activity stack of A -> B -> C -> D. Now if we launch D with the launch mode as “singleTask”, the new stack will be A -> B -> C -> D as usual.
Now if there is an activity stack of A -> B -> C -> D. If we launch activity B again with the launch mode as “singleTask”, the new activity stack will be A -> B. Activities C and D will be destroyed.
SingleInstance: Same as single task but the system does not launch any activities in the same task as this activity. If new activities are launched, they are done so in a separate task.
Example: Suppose there is an activity stack of A -> B -> C -> D. If we launch activity B again with the launch mode as “singleTask”, the new activity stack will be:
Task1 - A -> B -> C and Task2 - D
Start by making sure your Android application has the necessary read access permissions. Then, get access to the ContentResolver object by calling getContentResolver() on the Context object, and retrieving the data by constructing a query using ContentResolver.query().
The ContentResolver.query() method returns a Cursor, so you can retrieve data from each column using Cursor methods.
A ContentProvider provides data from one application to another, when requested. It manages access to a structured set of data. It provides mechanisms for defining data security. ContentProvider is the standard interface that connects data in one process with code running in another process.
When you want to access data in a ContentProvider, you must instead use the ContentResolver object in your application’s Context to communicate with the provider as a client. The provider object receives data requests from clients, performs the requested action, and returns the results.
FLAG_ACTIVITY_CLEAR_TASK is used to clear all the activities from the task including any existing instances of the class invoked. The Activity launched by intent becomes the new root of the otherwise empty task list. This flag has to be used in conjunction with FLAG_ ACTIVITY_NEW_TASK.
FLAG_ACTIVITY_CLEAR_TOP on the other hand, if set and if an old instance of this Activity exists in the task list then barring that all the other activities are removed and that old activity becomes the root of the task list. Else if there’s no instance of that activity then a new instance of it is made the root of the task list. Using FLAG_ACTIVITY_NEW_TASK in conjunction is a good practice, though not necessary.
OnRestoreInstanceState() - When activity is recreated after it was previously destroyed, we can recover the saved state from the Bundle that the system passes to the activity. Both the onCreate() and onRestoreInstanceState() callback methods receive the same Bundle that contains the instance state information. But because the onCreate() method is called whether the system is creating a new instance of your activity or recreating a previous one, you must check whether the state Bundle is null before you attempt to read it. If it is null, then the system is creating a new instance of the activity, instead of restoring a previous one that was destroyed.
onSaveInstanceState() - is a method used to store data before pausing the activity.
The onCreate() method is called once during the Activity lifecycle, either when the application starts, or when the Activity has been destroyed and then recreated, for example during a configuration change.
The onStart() method is called whenever the Activity becomes visible to the user, typically after onCreate() or onRestart().
- OnCreate(): This is when the view is first created. This is normally where we create views, get data from bundles etc.
- OnStart(): Called when the activity is becoming visible to the user. Followed by onResume() if the activity comes to the foreground, or onStop() if it becomes hidden.
- OnResume(): Called when the activity will start interacting with the user. At this point your activity is at the top of the activity stack, with user input going to it.
- OnPause(): Called as part of the activity lifecycle when an activity is going into the background, but has not (yet) been killed.
- OnStop(): Called when you are no longer visible to the user.
- OnDestroy(): Called when the activity is finishing
- OnRestart(): Called after your activity has been stopped, prior to it being started again
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