如何创建嵌套到其他活动的活动

Question

我正在尝试向MapDisplay创建MainActivity活动，但我有这个错误。

AndroidManifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.fin2"
android:versionCode="1"
android:versionName="1.0" >

   <uses-sdk
    android:minSdkVersion="12"
    android:targetSdkVersion="18" />

   <permission 
    android:name="com.example.fin2.permission.MAPS_RECEIVE"
    android:protectionLevel="signature"
    />

   <uses-permission android:name="com.example.fin2.permission.MAPS_RECEIVE"/>

   <uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission     android:name="com.google.android.providers.gsf.permission.READ_GSERVICES"/>
<!-- The following two permissions are not required to use
     Google Maps Android API v2, but are recommended. -->
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>


<uses-feature
    android:glEsVersion="0x00020000"
    android:required="true"/>


     <application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >

       <meta-data
            android:name="com.google.android.maps.v2.API_KEY"
            android:value="AIzaSyBubW3lo3wUzhklDRREUtma1xMl5GBMAIM"/>

       <activity
        android:name="com.example.fin2.MainActivity"
        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=".Map_Display_Activity"      
        />
    </application>

   </manifest>

和我的源代码

package com.example.fin2;



import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.Toast;

public class MainActivity extends Activity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
}

        @Override
        public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.main, menu);

    return true;
}

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
    // TODO Auto-generated method stub

    switch (item.getItemId()) {

    case R.id.display_map :

        Intent intent = new Intent(MainActivity.this,      Map_Display_Activity.class);
        startActivity(intent);

        return true;

    case R.id.autres :
        return true;

    case R.id.quitter:
        finish();
        return true;


    }
    return false;
}

   public class Map_Display_Activity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);

        setContentView(R.layout.map_display);

        Intent intent = getIntent();

        if (intent != null) {
            Toast.makeText(Map_Display_Activity.this, "Diplay Map", Toast.LENGTH_SHORT).show();

        }
    }

}

}

错误代码：

android.content.ActivityNotFoundException: Unable to find explicit activity class {com.example.fin2/com.example.fin2.MainActivity$Map_Display_Activity}; have you declared this activity in your AndroidManifest.xml?