Run Activity with Intent without knowing the class

I was having a problem this evening where I had to call an activity that I didn't want to know the class name. My problem was exactly this: I have several activities, each with a String id. And in activity A I call goToScreen("b"); to load activity B.

To make this work one need to do this:

public void goToScreen(String id) {
  PackageManager pm = androidContext.getPackageManager();
  Intent intent = new Intent("com.myproject.screen."
    + id.toUpperCase());
  intent.addCategory(Intent.CATEGORY_DEFAULT);

  ResolveInfo ri = pm.resolveActivity(intent,
    PackageManager.MATCH_DEFAULT_ONLY);

  if (ri != null) {
   Intent i = new Intent();
   i.setClassName(ri.activityInfo.applicationInfo.packageName,
     ri.activityInfo.name);
   androidContext.startActivity(i);
  }
 }

This code will call an activity mapped on AndroidManifest.xml like this:

<activity android:label="@string/app_name" android:name=".AvisoActivity">
   <intent-filter>
      <action android:name="com.myproject.screen.AVISO" />
      <category android:name="android.intent.category.DEFAULT" />
   </intent-filter>
</activity>


The DEFAULT category is not optional, as one may think. If you don't put both references (Java and XML) of the category, this code won't work. I don't know if it's a bug at Android or just a non-documented feature (which is a bug to me, anyway).

Also, don't forget to call resolveActivity with MATCH_DEFAULT_ONLY.

This is all for tonight and this blog post is more like of a reminder to myself. =)

BlocoDroid: Carnaval de Rua Rio 2011

Hoje estréia no Android Market, minha primeira aplicação para Android. O BlocoDroid é um guia da programação do Carnaval de Rua 2011 do Rio de Janeiro, com a lista de todos os blocos anunciados no Diário do Rio.

Útil para os folióids que não querem perder de vista os melhores blocos do Rio, mas também útil para aqueles que querem escapar dos engarrafamentos e bagunças causadas nessa época do ano. :-)

Para baixar o aplicativo, use o Barcode Scanner para instalar o programa no seu celular, com o QR Code acima. Ou pesquise por BlocoDroid no seu Android Market.

E bom Carnaval pra você!!

BlocoDroid for Android on AppBrain