Android Interview Questions Part 4 - Fragment

50. What is Toast in Android?

Android Toast can be used to display information for the short period of time. A toast contains message to be displayed quickly and disappears after sometime.

51. What are Loaders in Android?

Loader API was introduced in API level 11 and is used to load data from a data source to display in an activity or fragment. Loaders persist and cache results across configuration changes to prevent duplicate queries.

52. What is the difference between Dialog & DialogFragment?

A fragment that displays a dialog window, floating on top of its activity’s window. This fragment contains a Dialog object, which it displays as appropriate based on the fragment’s state. Dialogs are entirely dependent on Activities. If the screen is rotated, the dialog is dismissed. Dialog fragments take care of orientation, configuration changes as well.

53. Difference between margin & padding?

Padding will be space added inside the container, for instance, if it is a button, padding will be added inside the button. Margin will be space added outside the container.

54. What is View Group? How are they different from Views?

View: View objects are the basic building blocks of User Interface(UI) elements in Android. View is a simple rectangle box which responds to the user’s actions. Examples are EditText, Button, CheckBox etc. View refers to the android.view.View class, which is the base class of all UI classes.

ViewGroup: ViewGroup is the invisible container. It holds View and ViewGroup. For example, LinearLayout is the ViewGroup that contains Button(View), and other Layouts also. ViewGroup is the base class for Layouts.

55. What is the difference between a regular .png and a nine-patch image?

It is one of a resizable bitmap resource which is being used as backgrounds or other images on the device. The NinePatch class allows drawing a bitmap in nine sections. The four corners are unscaled; the middle of the image is scaled in both axes, the four edges are scaled into one axis.

56. Difference between RelativeLayout and LinearLayout?

Linear Layout — Arranges elements either vertically or horizontally. i.e. in a row or column.

Relative Layout — Arranges elements relative to parent or other elements.

57. What is ConstraintLayout?

It allows you to create large and complex layouts with a flat view hierarchy (no nested view groups). It’s similar to RelativeLayout in that all views are laid out according to relationships between sibling views and the parent layout, but it’s more flexible than RelativeLayout and easier to use with Android Studio’s Layout Editor.

58. When might you use a FrameLayout?

Frame Layouts are designed to contain a single item, making them an efficient choice when you need to display a single View.

If you add multiple Views to a FrameLayout then it’ll stack them one above the other, so FrameLayouts are also useful if you need overlapping Views, for example if you’re implementing an overlay or a HUD element.

59. What is Adapters?

An adapter responsible for converting each data entry into a View that can then be added to the AdapterView (ListView/RecyclerView).

60. How to support different screen sizes?

• Create a flexible layout — The best way to create a responsive layout for different screen sizes is to use ConstraintLayout as the base layout in your UI. ConstraintLayout allows you to specify the position and size for each view according to spatial relationships with other views in the layout. This way, all the views can move and stretch together as the screen size changes.
• Create stretchable nine-patch bitmaps
• Avoid hard-coded layout sizes — Use wrap_content or match_parent. Create alternative layouts — The app should provide alternative layouts to optimise the UI design for certain screen sizes. For eg: different UI for tablets
• Use the smallest width qualifier — For example, you can create a layout named main_activity that’s optimised for handsets and tablets by creating different versions of the file in directories as follows:res/layout/main_activity.xml — For handsets (smaller than 600dp available width)res/layout-sw600dp/main_activity.xml — For 7” tablets (600dp wide and bigger).
• The smallest width qualifier specifies the smallest of the screen’s two sides, regardless of the device’s current orientation, so it’s a simple way to specify the overall screen size available for your layout.

61. Outline the process of creating custom Views:

• Create a class that Subclass a view
• Create a res/values/attrs.xml file and declare the attributes you want to use with your custom View.
• In your View class, add a constructor method, instantiate the Paint object, and retrieve your custom attributes.
• Override either onSizeChanged() or onMeasure().
• Draw your View by overriding onDraw().

62. Briefly describe some ways that you can optimize View usage

• Checking for excessive overdraw: install your app on an Android device, and then enable the “Debug GPU Overview” option.
• Flattening your view hierarchy: inspect your view hierarchy using Android Studio’s ‘Hierarchy Viewer’ tool.
• Measuring how long it takes each View to complete the measure, layout, and draw phases. You can also use Hierarchy Viewer to identify any parts of the rendering pipeline that you need to optimise.

63. Bitmap pooling in android?

Bitmap pooling is a simple technique, that aims to reuse bitmaps instead of creating new ones every time. When you need a bitmap, you check a bitmap stack to see if there are any bitmaps available. If there are not bitmaps available you create a new bitmap otherwise you pop a bitmap from the stack and reuse it. Then when you are done with the bitmap, you can put it on a stack.