Contexts.md

Contexts

Android Context is normally required to construct widgets, check screen orientation, etc. However, one has to differentiate between two types of context: one obtained from an activity and one obtained from the application. The reason is that holding on to the activity context may cause memory leaks.

Macroid distinguishes between these two types of Context and passes them implicitly to prevent code bloat.

What are they

• macroid.AppContext holds the application context;
• macroid.ActivityContext holds a weak reference to the activity context, so that it’s safe to store it.

Including

To include the implicit contexts in your activity, inherit Contexts:

import macroid.Contexts

class MyActivity extends Activity with Contexts[Activity] {
  ...
}

If you use fragments from the support library (see the section on fragments):

class MyActivity extends FragmentActivity with Contexts[FragmentActivity] {
  ...
}

Finally, in a fragment (either android.app.Fragment or android.support.v4.app.Fragment):

class MyFragment extends Fragment with Contexts[Fragment] {
  ...
}

Usage

Most Macroid APIs require one or two of these contexts. If you use them inside an activity or a fragment, you are golden. However sometimes you need to pass the contexts to other methods:

import macroid.{ AppContext, ActivityContext }
import macroid.FullDsl._
import macroid.contrib._

def customTweak(implicit appCtx: AppContext) =
  // this one requires AppContext
  TextTweaks.large +
  text("foo")

def customLayout(implicit ctx: ActivityContext) =
  // layout bricks require ActivityContext
  l[LinearLayout](
    w[TextView],
    w[Button]
  )