Getactivity () is a null solution in Android _ios

Objective

In the day-to-day development, we often use ViewPager+Fragment to slide the view, in some parts of the logic we may need to take advantage of the context Context (for example, Basic Toast ), but because Fragment just attached to the Activity container of an attempt, if necessary to get the current Activity context Contextmust be getActivity() obtained by acquiring.

However, I do not know whether the program apes have encountered the occurrence of getactivity () when the null caused the program reported null pointer exception.

The reason can be attributed to the fact that we are:

(a) When switching fragment, will frequently be crash

(ii) Low system memory

(c) At the time of screen switching

....

This can result Activity in the system being reclaimed, but because fragment the lifecycle will not be reclaimed as it Actiivty is reclaimed, the problem of NULL getactivity () is caused.

Solve

Here's a summary of three solutions:

(i) Establishment of a context reference

First we look at Fragment the life cycle:

In Fragment the life cycle, the onAttach() onDetach() getActivity() method does not return when the lifecycle is in and between null . So we can fragment create a reference at initialization time Context .

fragmentdestroy the reference at the time of destruction.

The code is as follows:

 @Override public
 void Onattach [activity activity] {
  Super.onattach (activity);
  Mctx = Activity;//mctx is a member variable, context reference
 }

  @Override public
  void Ondetach () {
  super.ondetach ();
  Mctx = null;
  }

(ii) Rational use of getapplicationcontext ()

Using temporary variables to store context references in Method 1 Context can solve the problem to some extent. Because in Android,, Application , Service Activity all have context, getapplicationcontext() can get the global context, so as long as the program does not shut down, get context very difficult to null

(iii) Customizing your own application

The third method, in fact, is the same as the basic principle of the second method, which is about to be customized application temporarily to store application the owning context Context . In a program, application get the context by simple access Context .

The specific use is as follows:

(1) Register your application in the configuration list

<application
 android:name= ". MyApplication "
 android:icon=" @drawable/ic_launcher "
 android:label=" @string/app_name ">

(2) The OnCreate storage context in application and the creation of simple.

public class MyApplication extends application {

 private static MyApplication instance;

 @Override public
 void OnCreate () {
  super.oncreate ();
  Instance = this;//Store Reference
 } public

 static MyApplication getinstance () {return
  instance;
 }
}

Summarize

Here are just a few of the methods I've summed up, and of course there are other developers who have better advice to put forward, and that's better. Everybody together technology share, let everybody progress together!