The onSaveInstanceState () method should be called in the activity lifecycle whenever an activity is about to be destroyed, or possibly make a configuration change. This method allows the activity to save any needed information prior to being destroyed, such as data or UI state information, which can then be restored when the activity is recreated.
For example, when rotating the device or changing to a different language, the activity will be recreated based on the new orientation of the device or the new language selected. Since the activity will be destroyed, it is good practice to call onSaveInstanceState() before the activity is recreated to ensure any values are preserved.
It is important to note that the onSaveInstanceState () method may be called more than once between calls to onPause() and onStop(), and should therefore not be used to commit permanent changes.
When in the activity lifecycle is onSaveInstanceState () called?
onSaveInstanceState() is a method in the Activity class that is called before an activity is destroyed. It is part of the Activity lifecycle, and it is typically called between onPause() and onStop().
This is an important method to use to preserve any data and state information associated with the activity at the time it is destroyed, so it can later be restored to its original state when the activity is recreated.
This method is generally useful for situations such as when the user navigates away from the activity (such as rotating the device or switching to another activity), and you wish to store the activity’s current state in case the user later returns to the activity.
What is the use of onSaveInstanceState () method?
The onSaveInstanceState() method is used in an activity to save state information prior to the activity being destroyed and recreated. This is especially useful in situations where the user might go to a new activity and then decide to return back to the original activity.
By calling the onSaveInstanceState() method, the activity can save some state information, like UI states, user input, etc. , so that the user can resume from the same position when they return. This method is called by the system before the activity is destroyed and stores the state information in a Bundle object.
What’s the purpose of onSaveInstanceState and when it is invoked in the activity lifecycle?
The purpose of onSaveInstanceState is to save the state of a user-facing activity, so that it can be restored when the same activity is re-created. This is especially useful for activities with user input such as forms.
By saving the state of the activity, the user can pick up from where they left off in case the activity is destroyed due to a configuration change or memory pressure.
onSaveInstanceState is invoked when an activity is about to be destroyed and the activity is given a chance to save some of its state. This is done through a Bundle object in the onSaveInstanceState(Bundle OutState) method.
By the time this method has been called the activity is still active, but the user may not be able to interact with it at that moment. It is important to note that anything that is potentially waiting on a UI thread (such as a dialog or progress bar) can be lost in this situation.
Therefore, it is important to use onSaveInstanceState carefully.
The onSaveInstanceState(Bundle OutState) method is usually invoked by the system during the onStop() method of the activity lifecycle. This is important to note, as in certain situations like a configuration change, it is very possible for the Activity to never actually be stopped and therefore onSaveInstanceState may not be invoked.
When onStop is called in activity?
When an Activity is no longer visible to the user, it is considered to be in the “stopped” state. At this time, the system calls the onStop() method on the Activity, which indicates that it is no longer visible and can be killed if necessary in order to free up resources.
The onStop() method is intended to be used to release any resources that are not needed while the Activity is not visible. This may include database connections, network connections, or any other resources that can be safely freed while the Activity is not visible.
Once the Activity is visible again, the system calls the onStart() method to reinitialize any resources that need to be used.
In some cases, it may also be necessary to override the onStop() method in order to properly handle saving the state of the Activity, such as when the Activity is configured to be able to continue running in the background, even when it is no longer visible to the user.
What is the difference between the onPause () method and the onSaveInstanceState () method?
The onPause() and onSaveInstanceState() methods are two different life cycle methods in Android. The onPause() method is called when the activity is no longer visible to the user, either because it has been paused, stopped or destroyed.
This is generally used to stop or suspend activities and background services. The onSaveInstanceState() method is called when the activity is being stopped, but has a chance to save its state. This method is used to preserve the data or state of the activity, such as member variables, screen layout, user input, etc.
The saved state will remain active even if the activity is killed by the system due to lack of resources. When the activity is recreated, this stored state will be passed back to it via the onCreate() method.
While both methods are used to save data, they are different and should be used accordingly.
Is onPause always called before onDestroy?
No, onPause is not always called before onDestroy. Android will first call onPause if an Activity is paused or interrupted, such as when a PhoneCall is received or the Home Button is pressed. Then, if the Activity is no longer visible, Android will call onStop.
Once Android is finished with the Activity, it will call onDestroy. If the Activity is stopped due to rotation, onDestroy will not be called and onCreate will be called instead. It is important to be aware of which methods are called and when in order to perform the appropriate cleanup tasks.
What is the difference between onCreate () and onCreateView () lifecycle methods in fragment?
The onCreate() and onCreateView() lifecycle methods are two of the most important methods for managing a fragment. They are both part of the Fragment lifecycle, which outlines the different stages a Fragment goes through from its creation to its destruction.
The onCreate() method is the first of the lifecycle methods that is called when a Fragment is created. This is where the Fragment should perform initialization, such as inflating its View hierarchy, setting up instance variables, and any other initialization that might be necessary.
The onCreateView() method is a little more complex. This is the method where a Fragment should create and return its View hierarchy, which will be displayed to the user. In this method, Fragments can also perform additional operations such as attaching listeners to views and other tasks (such as populating the view hierarchy with data).
In summary, the onCreate() method is the first method to be called when a fragment is created and is responsible for initializing the Fragment and setting up its variables. The onCreateView() method is responsible for creating and returning the View hierarchy that will be displayed to the user.
What is called when the activity’s onCreate () method has been returned?
Once the activity’s onCreate() method has been returned, the activity has been fully launched and the main application code execution begins. The activity code can now start interacting with the user by providing data, such as creating and displaying views, retrieving data from the network, or processing user interactions.
This is called the activity’s main or main loop in which the application architecture is responsible for managing the various user initiated and system triggered events that occur as the user interacts with the device.
The activity’s main loop also handles any view transitions, such as switching between different activities, that are triggered by user interactions. This main loop continues until the activity is destroyed by the system when the user leaves the application or when the device runs out of memory.
At this point, the activity’s onDestroy() method is called, which signals the end of the activity lifecycle.
How UI state is managed with ViewModel?
ViewModels are the components that are responsible for managing the UI state in the MVVM architecture. They act as an intermediary between the UI and the models, allowing data manipulation to take place without having to be explicitly defined within the view.
ViewModels contain properties for the UI elements to bind to which can then be updated by the model data. This helps keep the view informed of any changes that may occur within the application. For example, if the application has a list of items that can be edited, then the ViewModel would contain a list of the items, and any changes to the list would be reflected on the view.
It also allows for easier data encapsulation and decoupling of the UI data from the models. ViewModels are especially useful when dealing with multiple views as they can keep track of the current UI state while also decoupling the UI from the models.
What is saving state?
Saving state is the process of persisting important information in a program, such as user-entered data, game scores, and other data pertinent to the functionality of the program. This data is stored in memory and is used to maintain the state of the program in between program executions.
Saving state is important for programs to function as intended and to provide user convenience. Examples include allowing a user to save their web browser history and allowing a game to save the user’s progress.
Saving state can be done through cookies, local storage, or a database; however, the most secure way is to store state information in a database. This ensures the data is kept secure and the application can always retrieve the data if needed.
When onSaveInstanceState () is called?
onSaveInstanceState () is a method in the Android Activity class that is called when the activity’s state needs to be saved. It is called before an activity is destroyed so that if the activity needs to be recreated later, its state can be restored.
This allows users to navigate away from an activity without losing their progress. Examples of state information that can be saved include the activity’s UI state, database information, and any data associated with the activity.
onSaveInstanceState () can also be used to store any data the user wants to back up before the activity is destroyed.
How do I save an instance state in fragment?
Saving an instance state in a fragment requires two different steps. First, you must override the onSaveInstanceState() method in your fragment and supply the save state Bundle in the onCreate() method.
This ensures that your activity can be restored to its previous state when the activity is re-created.
The second step is to create and populate a Bundle object within the onSaveInstanceState() method. The save state Bundle can contain primitive data types, Parcelable classes, Bundles and so on. To save an instance state in the fragment, add each desired object (or primitive type) to the Bundle using a unique key-value pair.
For example, if you want to store a String in the instance state Bundle, you can add it with the following code:
String myString = “myStringValue”;
Bundle outState = new Bundle();
outState.putString(“MyString”, myString);
You can also save and restore an entire object by implementing the Parcelable interface. This is done using the readFromParcel() and writeToParcel() methods.
Once the Bundle is ready, you must call the putExtras() or putParcelable() method on the save state Bundle so it can be stored. To restore the fragment to its previous state, simply use the Bundle in the onCreate() method.
By following the above steps, you can easily save an instance state in a fragment.
What is called first onCreate or onCreateView?
OnCreate is the first method called when creating an Activity. OnCreateView is then called after the onCreate method once the view hierarchy has been set up. The onCreateView method is used to inflate the layout, create the view and then return the view hierarchy.
This is important as the app needs to have a view in which to interact with the user and render the layout.
Is onAttach called before onCreate?
No, onAttach is not called before onCreate. onAttach is called when a fragment is first associated with an activity, as part of FragmentTransaction. commit(). After the FragmentTransaction is committed, the onCreate method is called.
So onCreate is always called after onAttach.