Android UI
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Android UI Presentation Transcript

  • 1. Developing Efficient Android UI
  • 2. Adapters in Android
    • An Adapter object acts as a bridge between an View and the underlying data for that view.
    • One side of the adapter is a data structure like a Java object storing data. the other side of the adapter, there is view that the data structure was transformed into.
    • The Adapter is also responsible for making a View for each item in the data set .
  • 3.  
  • 4.
    • Considering Adaptor for the List View
    • Each List item in the List View would be calling its “ getView() ” method.
    • This method would return a view for the List.
    • But creating a new View for each list item would be complicated, and the UI would be slow down.
    • Instead of creating new View for each item, Recycler save these view and passes it to the Adapter.
    • Adapter uses these view sent by the recycler, when it has to produce any new views.
  • 5. View Holders
    • View Holders hold some data that related to an item to the view.
    • View Holders minimizes the amount of work, while writing the same piece of code again and again.
    • These are used while creating the views, where we have to use more than one time.
    • (TextView)findViewById(R.Id.text);
    • (ImageView)findViewById(R.Id.Icon);
    • By using the View Holders, the views are saved into a class variable and can be called when needed.
    • holder.text = (TextView)findViewById(R.id.text);
    • holder.icon = (ImageView)findViewById(R.id.icon);
    • convertView.setTag(holder);
    • A tag can hold any kind of object, that can be set on the view.
  • 6.  
  • 7. Backgrounds
    • Backgrounds can be any bitmap images or Colors or any resource from drawable directory.
    • The background will completely fills the view.
    • Scaling a bitmap at runtime would be difficult as it has to fill the complete view.
    • Instead pre-scale the bitmap and then set it as background.
    • Else use the solid colors as background to fill the view.
    • This would increase the frame rate 50 frames per sec. (In normal we have 25 frames per sec).
  • 8. Pre-scaling a bitmap Bitmap.createScaledBitmap( originalImage, //bitmap to resize view.getwidth() //new width view.getHeight() //new Height true); //bi-linear filterring
  • 9. Drawing and Invalidating
    • Invalidate is a method used to redraw
    • Using invalidate method the entire screen is redrawn again.
    • This may consume some time to return to the normal state.
    • While invalidating two areas on the screen (say, top right and bottom left of the screen) the frame work would take the union of the area and redraws.
    • Solution for these problems would be:
    • invalidate(Rect)
    • and
    • invalidate(left, top, right, bottom)
    • Frames would be increased to 50 per sec. (normally 18 frames)
  • 10. Views and Layouts
    • View is a basic building block of the user interface component.
    • A view occupies a rectangle area on the screen and is responsible for drawing and event handling.
    • UI containing many Views would make the application to run slower as it has to load every view accordingly.
    • Drawing of objects on many views is a difficult task and requires more time to start an activity.
    • This may cause stackOverflow Exception (as the stack size in android is 8kb).
    • Deep hierarchies makes the UI very slow.
  • 11. Compound Drawables
    • <Linearlayout android:orientation = “horizantal”
    • android:layout_width = “fill_parent”
    • android:layout_height = “wrap_content” />
    • <TextView android:layout_width = “wrap_content”
    • android:layout_height = “wrap_content
    • android:text = “@string/hello” />
    • <ImageView android:layout_width = “wrap_content”
    • android:layout_height = “wrap_content”
    • android:src = “@drawable/icon” />
    • </Linearlayout>
    The above code can be written as: <TextView android:layout_width = “wrap_content” android:layout_height = “wrap_content” android:text = “@string/hello” android:drawableLeft = “@drawable/icon” />
  • 12. View Stub in android
    • View Stub is a dumb and lightweight view.
    • It has no dimensions and does not participate in Layouts.
    • View Stud is a feature that allows runtime inflation of views.
    • <ViewStub
    • android:id=“@+id/stub”
    • android:inflateId=“@+id/panel_import”
    • android:lalyout = “@layout/progress_overlay”
    • android:gravity = “bottom” />
    • Inflating a View Stub….
    • findViewById(R.id.stub).setVisibility(View.VISIBLE);
    • or
    • View importPannel = ((ViewStub)findViewById(R.id.stub)).inflate();
  • 13. Merge
    • The <merge /> can only be the root tag in the xml file.
    • This tag would reduces the levels of hierarchies in the xml layout file.
    • <merge xlms:android=“”>
    • <!– content -->
    • </merge>
  • 14. Relative Layout
    • Relative layout are powerful layout in android.
    • Relative layout replaces the Linear layout as the widgets are placed in either horizontal or vertical way.
    • Each child element is laid out in relation to other child elements.
    • Relationships can be established so that children will start themselves where a previous child ends.
    • Children can relate only to elements that are listed before them.
  • 15. Custom Views
    • Custom Views are very simple to use.
    • Just need to override only two methods.
    • onDraw(Canvas canvas)
    • onMeasure(int Width, int height)
    • We can define the dimensions of the view.
  • 16. Custom Layouts
    • Custom Layouts are used to define user defined layouts instead of using the pre-defined layouts.
    • Using custom layout, user can define:
    • height and width of the layout
    • Childs residing on the layout
    • Visibility of the children during runtime.
    • To define custom layout,
    • A class should extend ViewGroup
    • override onMeasure and onLayout methods.