AsyncTask In Android 


onPreExecute(), invoked on the UI thread before the task is executed.

This step is normally used to setup the task, for instance by showing a progress bar in the user interface.

doInBackground(Params...), invoked on the background thread immediately after onPreExecute() finishes executing.

This step is used to perform background computation that can take a long time.

The parameters of the asynchronous task are passed to this step.

The result of the computation must be returned by this step and will be passed back to the last step.

This step can also use publishProgress(Progress...) to publish one or more units of progress. 

These values are published on the UI thread, in the onProgressUpdate(Progress...) step.

onProgressUpdate(Progress...), invoked on the UI thread after a call to publishProgress(Progress...). 

The timing of the execution is undefined. This method is used to display any form of progress in the user interface while the background computation is still executing. 

For instance, it can be used to animate a progress bar or show logs in a text field.

onPostExecute(Result), invoked on the UI thread after the background computation finishes. 

The result of the background computation is passed to this step as a parameter.

RecyclerView vs. ListView

With the advent of Android Lollipop, the RecyclerView made its way officially. The RecyclerView is much more powerful, flexible and a major enhancement over ListView. I will try to give you a detailed insight into it.

1) ViewHolder Pattern

In a ListView, it was recommended to use the ViewHolder pattern but it was never a compulsion. In case of RecyclerView, this is mandatory using the RecyclerView.ViewHolder class. This is one of the major differences between the ListView and the RecyclerView.

It makes things a bit more complex in RecyclerView but a lot of problems that we faced in the ListView are solved efficiently.

2) LayoutManager

This is another massive enhancement brought to the RecyclerView. In a ListView, the only type of view available is the vertical ListView. There is no official way to even implement a horizontal ListView.

Now using a RecyclerView, we can have a

i) LinearLayoutManager - which supports both vertical and horizontal lists,

ii) StaggeredLayoutManager - which supports Pinterest like staggered lists,

iii) GridLayoutManager - which supports displaying grids as seen in Gallery apps.

And the best thing is that we can do all these dynamically as we want.

3) Item Animator

ListViews are lacking in support of good animations, but the RecyclerView brings a whole new dimension to it. Using the RecyclerView.ItemAnimator class, animating the views becomes so much easy and intuitive.

4) Item Decoration

In case of ListViews, dynamically decorating items like adding borders or dividers was never easy. But in case of RecyclerView, the RecyclerView.ItemDecorator class gives huge control to the developers but makes things a bit more time consuming and complex.

5) OnItemTouchListener

Intercepting item clicks on a ListView was simple, thanks to its AdapterView.OnItemClickListenerinterface. But the RecyclerView gives much more power and control to its developers by theRecyclerView.OnItemTouchListener but it complicates things a bit for the developer.

In simple words, the RecyclerView is much more customizable than the ListView and gives a lot of control and power to its developers.

Difference between abstract class and interface ?

1) Abstract class can have abstract and non-abstract methods.

    Interface can have only abstract methods.

2) Abstract class doesn't support multiple inheritance.

    Interface supports multiple inheritance.

3) Abstract class can have final, non-final, static and non-static variables.

    Interface has only static and final variables.

4) Abstract class can have static methods, main method and constructor.

    Interface can't have static methods, main method or constructor.

5) Abstract class can provide the implementation of interface.

    Interface can't provide the implementation of abstract class.

6) The abstract keyword is used to declare abstract class.

    The interface keyword is used to declare interface.

How to stop Asynctask Thread in Android ?

if (loginTask != null && loginTask.getStatus() != AsyncTask.Status.FINISHED)

{

    loginTask.cancel(true);

}

Where loginTask is object of your AsyncTask

Difference between an IntentService and a Service ?

When to use ?

The Service can be used in tasks with no UI, but shouldn't be too long. If you need to perform long tasks, you must use threads within Service.

The IntentService can be used in long tasks usually with no communication to Main Thread. If communication is required, can use Main Thread handler or broadcast intents. Another case of use is when callbacks are needed (Intent triggered tasks).

How to trigger ?

The Service is triggered by calling method startService().
The IntentService is triggered using an Intent, it spawns a new worker thread and the method onHandleIntent() is called on this thread.

Triggered From

The Service and IntentService may be triggered from any thread, activity or other application component.

Runs On

The Service runs in background but it runs on the Main Thread of the application.
The IntentService runs on a separate worker thread.

Limitations / Drawbacks

The Service may block the Main Thread of the application.
The IntentService cannot run tasks in parallel. Hence all the consecutive intents will go into the message queue for the worker thread and will execute sequentially.

When to stop?

If you implement a Service, it is your responsibility to stop the service when its work is done, by calling stopSelf() or stopService(). (If you only want to provide binding, you don't need to implement this method).
The IntentService stops the service after all start requests have been handled, so you never have to call stopSelf().

What is portable wi-fi hotspot?

Portable Wi-Fi Hotspot allows you to share your mobile internet connection to other wireless device. For examples, using your Android-powered phone as a Wi-Fi Hotspot, you can use your laptop to connect to the Internet using that access-point.

What is the difference between a regular bitmap and a nine-patch images?

In general, a Nine_patch image allows resizing that can be used as background or other image size requirements for the target device. The Nine-patch refers to the way you can resize the image: 4 corners that are unscaled, 4 edges that are scaled in 1 axis, and the middle one that can be scaled into both axes