Certified Android Apps Developer Android Events

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Android Events

Input Events

On Android, there's more than one way to intercept the events from a user's interaction with your application. When considering events within your user interface, the approach is to capture the events from the specific View object that the user interacts with. The View class provides the means to do so.

Within the various View classes that you'll use to compose your layout, you may notice several public callback methods that look useful for UI events. These methods are called by the Android framework when the respective action occurs on that object. For instance, when a View (such as a Button) is touched, the onTouchEvent()method is called on that object. However, in order to intercept this, you must extend the class and override the method. However, extending every View object in order to handle such an event would not be practical. This is why the View class also contains a collection of nested interfaces with callbacks that you can much more easily define. These interfaces, called event listeners, are your ticket to capturing the user interaction with your UI.

While you will more commonly use the event listeners to listen for user interaction, there may come a time when you do want to extend a View class, in order to build a custom component. Perhaps you want to extend the Buttonclass to make something more fancy. In this case, you'll be able to define the default event behaviors for your class using the class event handlers.

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