Sunday , November 28 2021

Event Handling in Android – Android Developer Guide

Event Handling in Android – Android Developer Guide – In the previous chapter, we discussed first and foremost the concept needed to create an Android App.

Different types of Layouts in detail so that whenever you think about creating an Android App, you know Be sure what will be the best Appropriate Layout for a specific activity to fulfill this kind of need. That is, you can choose the best possible layout for every activity of your Android App.

Although so far we have created many examples to understand different types of Layouts properly, but none of them have any TextView, EditText or Button Control on the User Interface of any of the Example App perform any kind of Action i.e. an Action. No Response to.

For example, there is no Output Return when you click the Button, or there is no Data Validation on entering the wrong name or Email in EditText to inform that the Input Name or Email Address is not correct.

Whereas any Graphical User Interface has only justification when it generates some sort of Output by Response / Handle to some kind of Action / Event. In the language of Modern Programming, this GUI Programming is known as Event Driven Programming.

Therefore, first of all you need to understand Java’s Event Driven Programming Model properly, only then you can give life to any of your Android App i.e. Create Useful Responsive Android App and in this chapter we will be using different types of Simple Examples. We will try to understand the Programming Model properly so that you can better understand how to implement the Event Handling Mechanism for the Graphical User Interface under the Android Framework.

Event Handling Mechanis

However if you know the UI Controls and Event Handling Mechanism of AWT / Swing of Java, then you will not need to learn much to create a Responsive Android App because Java’s Event Handling Mechanism follows a standard Approach that Java 1.2 is the same to date.

Based on the same Standard Event Handling Mechanism, the Android SDK allows defining an Event Handler in a total of 5 ways and when an Android Developer creates an Android App, then according to the different Situation it should be one of these five Best Creating your Event Handler is to choose the possible way.

Whenever an UI View Control performs an Event Trigger, the Android App does not provide any Response until it listens to that Event. To detect that an UI View Control has fired an Event, an Object of a Class is created in which the Appropriate Listener Interface is implemented to listen to that Fire occurring Event and that The Newly Created Object is assigned to that View UI Control.

As a result, the Assigned Listener Object is notified as soon as the UI View Control performs an Event Fire. That is, the Listener comes to know that the UI View Control has fired an Event and as soon as the Listener Notify happens, the Appropriate Event Handler Method implemented in the Listener Class becomes Execute.

Event Handling in Android – Android Developer Guide

In simplest terms, the Listener Object plays the role of Intermediator between the Trigger Event and the Callback Event Handler Method executed in Response to Event. Consequently, as soon as a Specific Event Fire is performed by any UI View Control, its Listener Object becomes Notified and executes any Specific Callback Event Handler Method associated with it to Response to the Event that fires.

If you understand this whole process by a simple to example, onClick Event is a very common event and it will be Event Fire when user clicks or taps on any UI View Control to be added to any Android App. is.

When onClick Event Fire is done by any UI View Control, then this event is notified by listening to the object of the class in which the OnClickListener Interface is implemented i.e. the Callback Event Handler of the onClick Event that is fired is defined. is. Then using the setOnClickListener () method, the Listener Object that is notifying is assigned to the View that has done the Event Fire.

In this way, a Connection is created between the Event Viewler implementing the Event Fire and the Event Handler implementing the Listener Interface. As a result, whenever the onClick Event Fire performs the corresponding UI View Control, it executes the Event Handler Method of the Associated Listener Class and is used to handle any type of Event Exactly.

Input Events and Event Handler Callbacks

When the user interacts with an Android App, the Android Framework provides a total of 5 different ways to capture different types of Input Evensts fired by different UI View Controls through which we can respond to those Events. Handler Callbacks Can Implement.

But when we talk about the events that fire due to the User Interaction done with the User Interface of our Android App, the first thing we need to do is to capture an event that is fired by a Specific View Object and to do so The facility provides us with View Class.

All the UI View Controls we use in the layout of our Android App are all Objects of some View Class and each View Class is able to handle any UI Event through many Public Callback Methods. That is, Execute is in Response of Fired Event. These Public Callback Methods are called by the Android Framework when the Assocaited UI View Control from it performs an Event Fire in the form of Action that is to be handled by that Callback Method.

For example when a Placed Button (UI View Control) object is touched on the Layout of an Android App, the Callback Method named onTouchEvent () is invoke for that Button by the Android Framework.

Event Handling in Android – Android Developer Guide

But by extending the View Class of each UI Control, it is not practically possible to handle the Assocaited Event through its Public Callback Methods. That is why every View Class also has a collection of Nested Interfaces that contain Declaration of Public Callback Methods related to handling events that are fired by that UI View Control.

The collection of these interfaces nested in various View Classes is called Event Listener which can be easily implemented in any class and defined in these Implemented Classes by Android Platform to Response Events that fire from UI View Control. Public callback methods are executed or invoke.

To put it simply, when the user interacts with the user interface of our Android App, then the mechanism of Respout them by capturing various events that are fired by Layout’s various UI View Controls and then executing their Handler Callback Methods. Are received by listeners.

Although these Event Listeners are used to listen to most types of Events that are fire due to User Interaction, there are times when we need a View Class to create a Custom UI View Control. Extending its functionalities has to be done while inherit.

In this type of situation we can define Default Event Behaviors using Event Handlers in our Custom UI Control’s View Class, which is one of the 5 methods used to handle Events under Android Framework There is a way and we will learn about this in further detail but first we get to understand Event Listeners a little more deeply which is the basic foundation of Event Handling under Android Framework.

onClick () Callback Method
onLongClick () Callback Method
onFocusChange () Callback Method
onKey () Callback Method
onTouch () Callback Method
onCreateContextMenu () Callback Method

Read Also – Method Chaining in Java Android– Unnamed Objects in Android

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