Determining the Size of an Android View or Screen at Run Time
For efficient bitmap handling or dynamic View creation in an App the area that a widget or layout is using needs to be known. If no fixed sizes are allocated at design time the size of a View may not be known until an App is executed. This is because of the wide range of display sizes that Android supports. The example code snippets in this articles shows how to read the screen size and the size of Views as the App runs. To run the example code you will need to create a new Android project (those new to Android programming can view the article Your First Android Hello World Java Program to see how), we called our App View Size.
In the layout designer for activity_main.xml (or whatever you called your layout) add another TextView, called textXY, next to the existing Hello world! widget. Change the Text on the first TextView to X,Y. Add this code to the oncreate method in MainActivity.java (or whatever class you are using), you will need an imports for TextView and DisplayMetrics. :
//object to store display information
DisplayMetrics metrics = new DisplayMetrics();
//get display information
//show display width and height
This is the code running on an AVD with a 320×480 screen:
He is the layout used for this screen: Continue reading
In Android Get View Defined in XML in Activity Code
The UI screens for an App can be designed outside of the code. They are stored in XML files. This eases support for multiple screen sizes and types and helps with software maintenance. Classes in the Android SDK have methods used to access the UI components. Screens are composed of various implementations of the Android View class. The major sub-classes for Views are widgets and ViewGroups. The widget class is not to be confused with Widgets that can be added to the Android home screen. Instead View widgets are the normal components with which the Android device users interact, including the Button, Checkbox, EditText (a text box), ImageView, RadioButton, ProgressBar, TextView (label) and many more. Several widgets sit in a ViewGroup which provides a container for laying out components. Different ViewGroups provide different types of layouts, including RelativeLayout, LinearLayout, ScrollView, WebView and others. ViewGroups can contain other ViewGroups as well as widgets therefore building complex displays by nesting different Views is possible.
Create a Basic Android Screen
For this tutorial create a new, simple Android App project and call it Button Demo (if you don’t know how see Your First Android Hello World Java Program). A simple screen that just has a button on it was created using the starting layout, we kept the default layout name of activity_main.xml. In Eclipse use the Package Explorer to open the activity_main.xml file (in the res/layout folder). Using the Graphical Layout view (selected via the tabs at the bottom of the editor window) delete the TextView, showing Hello world!, and drag and drop a Button from the Form Widgets folder onto the screen. This screen’s code is stored in the activity_main.xml file:
To show how this view is accessed from the App’s code the text on the button will be changed and it displays a message when it is clicked. Continue reading