Including Flags in the intent delivered to the startActivity().Using Android Manifest tag with attribute android:launchMode.In order to tackle the above deviations from the default, we are provided two modes. The back stack should be cleared to the root Activity when a user leaves the existing Activity.When starting a new Activity the existing instance is required to be brought from the back stack as we already mentioned.Instead, either a new task starts for the Browser or, if the Browser already has a task running in the background, that task is brought forward to handle the new intent. This means that if your application issues an intent to open the Android Browser, its activity is not placed in the same task as your application. When starting a new Activity, it is required to start in a new Task rather than being placed in the back stack of the existing Task.Īs an e xample, the Android Browser application declares that the web browser Activity should always open in its own Task.The Android Developer Guide lists some of those situations as follows: There are few situations where we would want the manage the Task as a deviation from the default behavior. We will see how to do that in the text to follow. This particular behavior is undesirable and the main concern of this article is learning to control the back stack so that an Activity exists in a single instance at a time and with relation to its originator Activity. In this case, the Back button reveals the instance of the same Activity multiple times with its state in the order is was created. If an Activity is started from multiple Activities, then a new instance of that Activity is created and pushed on the stack rather than bringing the previous instance of that Activity to the top. We can derive from the above text a very important result. When the user returns to the Task again, only the root Activity is restored ( this behavior can be overridden as we will see later). When multiple tasks are in the background or when the user leaves the Task for a long time, the system in order to recover memory clears the Task of all the Activities except the root Activity.It is then brought to the foreground by clicking the launcher icon ( this is the another role of the launcher icon that we mentioned earlier) or by selecting the task from the recent screens.It goes into the background when a new task is created or when the Home button is pressed.Activities of different applications invoked by the intent are put into the same Task.When the back stack goes empty then the Task ceased to exist.When the last Activity is removed from the back stack, then the Task terminates to the screen that was last running before the creation of the Task ( in our case the launcher screen). The Back button then keeps on popping the current Activities and restoring the previous activities.This destroys the Activity and the previous Activity resumes with its state restored. When the Back button is pressed then the current Activity is popped from the top of the back stack.The subsequent new Activities keep on piling the back stack.The system retains the current state of this Activity’s user interfaces like text in the form, scroll position etc. The previous Activity moves below this new Activity in the back stack and is stopped.When the current Activity starts another Activity, then the new Activity is pushed on top of the stack and takes focus.The application launcher creates a new Task with the main Activity created and placed in the root of the back stack ( It has another role that we will review later).We will now go through the default behavior of the Task and the Back Stack. The navigation of the back stack is done with the help of the Back button. The Activities in the Stack are never rearranged. The Stack has LIFO structure and stores the activities in the order of their opening. A Task is a collection of activities that user interact when performing a certain job.Ī Task holds the Activities, arranged in a Stack called Back Stack. Android defines the unit of a sequence of user interactions as Task. Let’s review the Android’s default implementations in the above regards. Android developer guide says: Each Activity should be designed around a specific kind of action the user can perform and can start other activities. The Android design already has taken a very good care of providing a smooth user experience in terms of managing the screen flows. One of the most important aspects of achieving the above is to design a proper forward and backward navigations. This relation should be designed with the focus of developing an effortless and pattern forming strategy from the user’s perspective. The relation that each Activity holds with respect to other is very crucial for a good user experience. Android Activities are the logical construct of the screens that we want a user to navigate through.
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