Android: Unable to find explicit activity class... startActivity from a PreferenceActivity

I'm trying to start a new Activity from a PreferenceActivity. However, it fails with "Unable to find explicit activity class. Have you declared this activity in your AndroidManifest.xml?"

Well, yeah, I declared it:

<application [......] android:debuggable="true">
    <activity android:name=".AlarmSettings"
              android:label="@string/app_name">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

    <activity android:name=".FlashLightActivity"></activity>

    <receiver
        android:name="AlarmReceiver"
        android:process=":remote" >
    </receiver>
</application>

AlarmSettings is my PreferenceActivity. AlarmSettings calls FlashLightActivity this way:

Intent i = new Intent(AlarmSettings.this, FlashLightActivity.class);
startActivity(i);

And this is FlashLightActivity:

public class FlashLightActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.flashlight);
   }    
}

... I don't know what to do. Any ideas?

I had this problem too. If you read carefully the error on the logcat, you will know what to do.

You have to declare the activity in the AndroidManifest.xml

    <activity
        android:name=".TheNameOfMyActivity"
        android:label="@string/app_name" >
        <intent-filter>
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

For me this error occurred because I had moved my activity class file to a different package and for some reason Eclipse didn't refactor it correctly. Always use a fully qualified name for your activity and double-check that it is accurate.

When starting an activity from inside another you need to provide your AndroidManifest file the parent child relationship, to ensure that the started activity will return its result to you requires parent activity. example,

<activity
            android:name="ACTIVITY TO BE STARTED"
            android:label="@string/TITLE"
            android:screenOrientation="landscape" >
             <meta-data
                android:name="android.support.PARENT_ACTIVITY"
                android:value="ACTIVITY STARTED FROM?RETURNING TO" />
        </activity>