Qu’est-ce que la méthode getBaseContext dans Android ?



par

The method getBaseContext() is only relevant when you have a ContextWrapper.

Android provides a ContextWrapper class that is created around an existing Context using:

  1. ContextWrapper wrapper = new ContextWrapper(context); 

The benefit of using a ContextWrapper is that it lets you “modify behavior without changing the original Context”. For example, if you have an activity called myActivity then can create a View with a different theme than myActivity:

  1. ContextWrapper customTheme = new ContextWrapper(myActivity) { 
  2. @Override 
  3. public Resources.Theme getTheme() {  
  4. return someTheme; 
  5. } 
  6. } 
  7. View myView = new MyView(customTheme); 

ContextWrapper is really powerful because it lets you override most functions provided by Context including code to access resources (e.g. openFileInput(), getString()), d'interagir avec d'autres composants (par exemple sendBroadcast(), registerReceiver()), de demander des permissions (par exemple checkCallingOrSelfPermission()) et de résoudre les emplacements du système de fichiers (par exemple getFilesDir()). ContextWrapper est vraiment utile pour contourner les problèmes spécifiques aux appareils/versions ou pour appliquer des personnalisations uniques à des composants tels que Views qui nécessitent un contexte.

La méthode getBaseContext() peut être utilisée pour accéder au Contexte "de base" que le ContextWrapper enveloppe. You might need to access the “base” context if you need to, for example, check whether it’s a Service, Activity or Application:

  1. public class CustomToast { 
  2. public void makeText(Context context, int resId, int duration) { 
  3. while (context instanceof ContextWrapper) { 
  4. context = context.baseContext(); 
  5. } 
  6. if (context instanceof Service)) { 
  7. throw new RuntimeException("Cannot call this from a service"); 
  8. } 
  9. ... 
  10. } 
  11. } 

Or if you need to call the “unwrapped” version of a method:

  1. class MyCustomWrapper extends ContextWrapper { 
  2. @Override 
  3. public Drawable getWallpaper() { 
  4. if (BuildInfo.DEBUG) { 
  5. return debugBackground; 
  6. } else { 
  7. return getBaseContext().getWallpaper(); 
  8. } 
  9. } 
  10. }