<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/prompt"
    />
<EditText
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:id="@+id/name"
    />
<Button
     android:layout_height="wrap_content"
     android:layout_width="wrap_content"
     android:text="@string/getversion"
     android:onClick="getVersion" />
<TextView  
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:id="@+id/versionInfo"
    />
</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="app_name">Get Application Version</string>
    <string name="prompt">Enter Package Name:</string>
    <string name="getVersion">Get Version</string>
    <string name="packageNotFound">Package not found.</string>
    <string name="packageInfo">Version code: %s, version name: %s</string>
</resources>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.android.appinfo"
      android:versionCode="1"
      android:versionName="1.0">
    <application android:label="@string/app_name" android:icon="@drawable/icon">
        <activity android:name="GetAppVersion"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

package com.android.appinfo;

import android.app.Activity;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.pm.Signature;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

public class GetAppVersion extends Activity
{
    private static final String LOG_TAG = "GetAppVersion";

    private EditText nameField;
    private TextView versionInfoField;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

  nameField = (EditText) findViewById(R.id.name);
  versionInfoField = (TextView) findViewById(R.id.versionInfo);
    }

    public void getVersion(View view) {
  CharSequence name = nameField.getText();
  try {
      PackageInfo pkgInfo = getPackageManager().getPackageInfo(name.toString(), 0);
      versionInfoField.setText(String.format(
    getString(R.string.packageInfo),
    pkgInfo.versionCode, 
    pkgInfo.versionName
      ));
  }
  catch (PackageManager.NameNotFoundException e) {
      versionInfoField.setText(getString(R.string.packageNotFound));
  }
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<project name="AppInfo" default="help">
.
.
.
</project>

ant install