Android 中的上下文到底是什么，为什么需要它？

Question

I am new to Android development and Software development too. I keep seeing this term called - 'context' in Android code. I know that it's a class in android.content package, but I don't understand what exactly is it and why is it needed in so many places, especially in the constructors.

Can someone please explain this term to me.

Answer 1

As the name suggests, its the context of current state of the application/object. It lets newly created objects understand what has been going on. Typically you call it to get information regarding another part of your program (activity, package/application)

You can get the context by invoking getApplicationContext(), getContext(), getBaseContext() or this (when in the activity class).

Typical use of context:

Creating New objects: Creating new views, adapters, listeners:

TextView tv = new TextView(getContext()); ListAdapter adapter = new SimpleCursorAdapter(getApplicationContext(),..);

Accessing Standard Common Resources: Services like LAYOUT_INFLATER_SERVICE, SharedPreferences:

context.getSystemService(LAYOUT_INFLATER_SERVICE)
getApplicationContext().getSharedPreferences(name, mode);

Accessing Components Implicitly: Regarding content providers, broadcasts, intent

getApplicationContext().getContentResolver().query(uri,...);

Its copy from here