Android App- Unofficial Android Market(Play Store) API

I want to display a List of some Apps using the unofficial Android Market(Play Store) API(http://code.google.com/p/android-market-api).

But I always get Errors. Does somebody have an idea why I get Errors?

Here is my Code:

 package iStore.App.Android;
 
  import java.util.List;
 
  import android.app.Activity;
  import android.os.Bundle;
  import com.gc.android.market.api.MarketSession;
  import com.gc.android.market.api.MarketSession.Callback;
  import com.gc.android.market.api.model.Market.App;
  import com.gc.android.market.api.model.Market.AppsRequest;
  import com.gc.android.market.api.model.Market.AppsResponse;
  import com.gc.android.market.api.model.Market.ResponseContext;
 
  import android.provider.Settings.Secure;
  import android.util.Log;
  import android.widget.TextView;
 
 
    public class MainActivity extends Activity {
 /** Called when the activity is first created. */
 @Override
 public void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     setContentView(R.layout.main);
     final TextView textview = (TextView) findViewById(R.id.TextView);
 
     MarketSession session = new MarketSession();
     session.login("my email adresse","my passsword");
     String AndroidId = Secure.getString(this.getContentResolver(), Secure.ANDROID_ID);
     session.getContext().setAndroidId(AndroidId);
 
     String query = "google";
     AppsRequest appsRequest = AppsRequest.newBuilder()
             .setQuery(query)
             .setStartIndex(0).setEntriesCount(3)
             .setWithExtendedInfo(false)
             .build();
 
     Callback<AppsResponse> callback = new Callback<AppsResponse> () {
     public void onResult(ResponseContext context, AppsResponse response) {
 
 
 textview.setText("It worked");
 
     }
     };
     session.append(appsRequest, callback);
     session.flush();
     }
     }
 

I tried this in a Java Project. There it worked, but instead of

    String AndroidId = Secure.getString(this.getContentResolver(), Secure.ANDROID_ID);
 

I used my actual Android ID. But why does it not work in an Android App?

Thanks.

EDIT:
My LogCat:

    04-23 15:18:16.379: E/dalvikvm(4111): Could not find class 'com.gc.android.market.api.MarketSession', referenced from method iStore.App.Android.MainActivity.onCreate
 04-23 15:18:16.389: W/dalvikvm(4111): VFY: unable to resolve new-instance 11 (Lcom/gc/android/market/api/MarketSession;) in LiStore/App/Android/MainActivity;
 04-23 15:18:16.429: W/dalvikvm(4111): threadid=1: thread exiting with uncaught exception (group=0x40018560)
 04-23 15:18:16.429: E/AndroidRuntime(4111): FATAL EXCEPTION: main
 04-23 15:18:16.429: E/AndroidRuntime(4111): java.lang.NoClassDefFoundError: com.gc.android.market.api.MarketSession
 04-23 15:18:16.429: E/AndroidRuntime(4111):     at iStore.App.Android.MainActivity.onCreate(MainActivity.java:27)
 04-23 15:18:16.429: E/AndroidRuntime(4111):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
 04-23 15:18:16.429: E/AndroidRuntime(4111):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
 04-23 15:18:16.429: E/AndroidRuntime(4111):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
 04-23 15:18:16.429: E/AndroidRuntime(4111):     at android.app.ActivityThread.access$1500(ActivityThread.java:117)
 04-23 15:18:16.429: E/AndroidRuntime(4111):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
 04-23 15:18:16.429: E/AndroidRuntime(4111):     at android.os.Handler.dispatchMessage(Handler.java:99)
 04-23 15:18:16.429: E/AndroidRuntime(4111):     at android.os.Looper.loop(Looper.java:123)
 04-23 15:18:16.429: E/AndroidRuntime(4111):     at android.app.ActivityThread.main(ActivityThread.java:3729)
 04-23 15:18:16.429: E/AndroidRuntime(4111):     at java.lang.reflect.Method.invokeNative(Native Method)
 04-23 15:18:16.429: E/AndroidRuntime(4111):     at java.lang.reflect.Method.invoke(Method.java:507)
 04-23 15:18:16.429: E/AndroidRuntime(4111):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:874)
 04-23 15:18:16.429: E/AndroidRuntime(4111):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:632)
 04-23 15:18:16.429: E/AndroidRuntime(4111):     at dalvik.system.NativeStart.main(Native Method)
 

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