Android: Start Email-Activity with Preset Data (via Intents)

/* Create the Intent */
final Intent emailIntent = new Intent(android.content.Intent.ACTION_SEND);

/* Fill it with Data */
emailIntent.setType("plain/text");
emailIntent.putExtra(android.content.Intent.EXTRA_EMAIL, new String[]{"to@email.com"});
emailIntent.putExtra(android.content.Intent.EXTRA_SUBJECT, "Subject");
emailIntent.putExtra(android.content.Intent.EXTRA_TEXT, "Text");

/* Send it off to the Activity-Chooser */
context.startActivity(Intent.createChooser(emailIntent, "Send mail..."));

Android: Enable and Disable WiFi Programmatically

WifiManager wifi = (WifiManager) getSystemService(Context.WIFI_SERVICE);
wifi.setWifiEnabled(enabled);

Android: Recognize Incoming Phone Calls

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.telephony.Phone;
import android.telephony.PhoneStateIntentReceiver;
import android.util.Log;

public class ReactOnIncomingCall extends Activity {
     /** Used to recognize Messages from the
      * myPhoneStateChangedHandler. */
     final int PHONECALLSTATE_RECONGNIZE_ID = 0x539;
    
     /** Will notify us on changes to the PhoneState*/
     PhoneStateIntentReceiver myPsir = null;

    /** This Handler will react on the messages the
     * we made our PhoneStateIntentReceiver myPsir
     * notify us on. */
    Handler myPhoneStateChangedHandler = new Handler(){
          @Override
          public void handleMessage(Message msg) {

               // Recognize the Message by its what-ID
               if(msg.what == PHONECALLSTATE_RECONGNIZE_ID){

                    /* Our PhoneStateIntentReceiver myPsir
                     * now contains some recent data, we can grab. */
                    Phone.State myState = myPsir.getPhoneState();

                    // Put the Info to the logger for debugging
                    Log.d("PhoneCallStateNotified", myState.toString());

                    if(myState == Phone.State.RINGING){
                         // Celebrate =D
                    }             
               }
          }
    };
    
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle icicle) {
     // Set some simple layout
        super.onCreate(icicle);
        setContentView(R.layout.main);

      
        /* Create a new PhoneStateIntentReceiver
         * that will pass messages to the handler h
         * as it receives Intents we make it notify
         * us below*/
        this.myPsir = new PhoneStateIntentReceiver(this, myPhoneStateChangedHandler);
      
        /* As we want to get notified on changes
         * to the Phones-State we tell our
         * PhoneStateIntentReceiver myPsir,
         * that we wan to get notified with the ID
         * (PHONECALLSTATE_RECONGNIZE_ID) we pass to him
         */
        this.myPsir.notifyPhoneCallState(PHONECALLSTATE_RECONGNIZE_ID);
         
          /* Register the Intent with the system. */
        this.myPsir.registerIntent();
    }
}

Get Size and Orientation of the Screen of Android Device

/* First, get the Display from the WindowManager */
Display display = ((WindowManager) getSystemService(WINDOW_SERVICE)).getDefaultDisplay();

/* Now we can retrieve all display-related infos */
int width = display.getWidth();
int height = display.getHeight();
int orientation = display.getOrientation();

Android: Vibrate the phone for a given time or a certain pattern

Vibrator v = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);

// 1. Vibrate for 1000 milliseconds
long milliseconds = 1000;
v.vibrate(milliseconds);

// 2. Vibrate in a Pattern with 500ms on, 500ms off for 5 times
long[] pattern = { 500, 300 };
v.vibrate(pattern, 5);

For this to work, you will have to add the android.permission.VIBRATE permission to your Manifest.xml

Android: Get installed Applications with Name, Package Name, Version and Icon

class PInfo {
    private String appname = "";
    private String pname = "";
    private String versionName = "";
    private int versionCode = 0;
    private Drawable icon;
    private void prettyPrint() {
        log(appname + "\t" + pname + "\t" + versionName + "\t" + versionCode + "\t");
    }
}

private void listPackages() {
    ArrayList apps = getInstalledApps(false); /* false = no system packages */
    final int max = apps.size();
    for (int i=0; i
        apps.get(i).prettyPrint();
    }
}

private ArrayList getInstalledApps(boolean getSysPackages) {
    ArrayList res = new ArrayList();       
    List packs = getPackageManager().getInstalledPackages(0);
    for(int i=0;i
        PackageInfo p = packs.get(i);
        if ((!getSysPackages) && (p.versionName == null)) {
            continue ;
        }
        PInfo newInfo = new PInfo();
        newInfo.appname = p.applicationInfo.loadLabel(getPackageManager()).toString();
        newInfo.pname = p.packageName;
        newInfo.versionName = p.versionName;
        newInfo.versionCode = p.versionCode;
        newInfo.icon = p.applicationInfo.loadIcon(getPackageManager());
        res.add(newInfo);
    }
    return res;
}

Retrieve JSON from a REST web service

String result = queryRESTurl("http://location/of/wellformed/json.json");

    try{
        JSONObject json = new JSONObject(result);
        JSONArray nameArray = json.names();
        JSONArray valArray = json.toJSONArray(nameArray);
        for (int i = 0; i < valArray.length(); i++) {
            Log.i(TAG, "\n" + nameArray.getString(i)    + "\n\n" + "\n" + valArray.getString(i) + "\n");
        }
    }
    catch (JSONException e) {
        Log.e("JSON", "There was an error parsing the JSON", e);
    }



public String queryRESTurl(String url) {
    HttpClient httpclient = new DefaultHttpClient();
    HttpGet httpget = new HttpGet(url);
    HttpResponse response;
   
    try {
        response = httpclient.execute(httpget);
        Log.i(TAG, "Status:[" + response.getStatusLine().toString() + "]");
        HttpEntity entity = response.getEntity();
       
        if (entity != null) {
           
            InputStream instream = entity.getContent();
            String result = RestClient.convertStreamToString(instream);
            Log.i(TAG, "Result of converstion: [" + result + "]");
           
            instream.close();
            return result;
        }
    } catch (ClientProtocolException e) {
        Log.e("REST", "There was a protocol based error", e);
    } catch (IOException e) {
        Log.e("REST", "There was an IO Stream related error", e);
    }
   
    return null;
}