What is the difference between Fragment and FragmentActivity?

android, android-fragmentactivity, android-fragments

Solution

A `Fragment` is a section of an `Activity`, which has:

- its own lifecycle

- receives its own input events

- can be added or removed while the `Activity` is running.

A `Fragment` must always be embedded in an `Activity`.

`Fragments` are not part of the API prior to HoneyComb (3.0). If you want to use `Fragments` in an app targeting a platform version prior to HoneyComb, you need to add the Support Package to your project and use the `FragmentActivity` to hold your `Fragments`. The `FragmentActivity` class has an API for dealing with `Fragments`, whereas the `Activity` class, prior to HoneyComb, doesn't.

If your project is targeting HoneyComb or newer only, you should use `Activity` and not `FragmentActivity` to hold your `Fragments`.

Some details:

Use `android.app.Fragment` with `Activity`. Use `android.support.v4.app.Fragment` with `FragmentActivity`. Don't add the support package `Fragment` to an `Activity` as it will cause an Exception to be thrown.

A thing to be careful with: `FragmentManager` and `LoaderManager` have separate support versions for FragmentActivity:

If you are using a `Fragment` in an `Activity` (HoneyComb and up), call

- `getFragmentManager()` to get `android.app.FragmentManager`

- `getLoaderManager()` to get `android.app.LoaderManager`

if you are using a `Fragment` in a `FragmentActivity` (pre-HoneyComb), call:

- `getSupportFragmentManager()` to get `android.support.v4.app.FragmentManager`.

- `getSupportLoaderManager()` to get `android.support.v4.app.LoaderManager`

so, don't do

//don't do this
myFragmentActivity.getLoaderManager(); 
//instead do this:
myFragmentActivity.getSupportLoaderManager();

or

//don't do this:
android.app.FragmentManager fm = myFragmentActivity.getSupportFragmentManager();
//instead do this:
android.support.v4.app.FragmentManager fm = myFragmentActivity.getSupportFragmentManager()

Also useful to know is that while a fragment has to be embedded in an `Activity` it doesn't have to be part of the `Activity` layout. It can be used as an invisible worker for the activity, with no UI of its own.

Problem

Original source