Android programming

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Android programming

                                        
                                                  Content Provider
                              Applications can store their data in files, a SQLite database, preferences or any other mechanism that makes sense. A content provider, however, is useful if you want your application's data to be shared with other applications. A content provider is a class that implements a standard set of methods to let other applications store and retrieve the type of data that is handled by that content provider.
                              andbook - Android Programming
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                              Android User Interfaces
                              User Interfaces (UI) in Android can be built within two ways, by defining XML-Code or by writing Java-Code. Defining the GUI structure in XML is highly preferable, because as one knows from the Model-Viewer-Control principle that the UI should always be separated from the program-logic. Additionally adapting a program from one screen-resolution to another is a lot easier. Defining a UI in XML is very similar to creating a common HTML-document, where you have i.e. such a simple file: <html> <head> <title>Page Title</title> </head> <body> The content of the body element. </body> </html> Just the same as in Android’s XML-Layouts. Everything is well structured and can be expressed by tree-structures: <?xml?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="fill_parent"> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Hello World"/> </LinearLayout>
                              Hierarchy of Screen Elements
                              The basic functional unit of an Android application is the activity-an object of the class android.app.Activity. An activity can do many things, but by itself it does not have a presence on the screen. To give your activity a screen presence and design its UI, you work with views
                              andbook - Android Programming
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                              and viewgroups - basic units of user interface expression on the Android platform.
                              Views
                              A view is an object extending the base class android.view.View. It's a data structure whose properties store the layout and content for a specific rectangular area of the screen. A View object handles measuring, its layout, drawing, focus changes, scrolling, and key/gestures for the screen area it represents. The View class serves as a base class for all widgets - a set of fully implemented subclasses that draw interactive screen elements. Widgets handle their own measuring and drawing, so you can use them to build your UI more quickly. The list of widgets available includes i.e. TextView, EditText, Button, RadioButton, Checkbox, ScrollView, …
                              Viewgroups
                              A viewgroup is an object of class android.view.Viewgroup. As its name indicates, a viewgroup is a special type of view object whose function is to contain and manage a subordinate set of views and other viewgroups, Viewgroups let you add structure to your UI and build up complex screen elements that can be addressed as a single entity. The Viewgroup class serves as a base class for layouts - a set of fully implemented subclasses that provide common types of screen layout. The layouts give you a way to build a structure for a set of views.
                              A Tree-Structured UI
                              On the Android platform, you define an Activity's UI using a tree of view and viewgroup nodes, as shown in the diagram below. The tree can be as simple or complex as you need to make it, and you can build it up using Android's set of predefined widgets and layouts or custom view types that you create yourself.