android学开发：按钮点击

package a.b.com;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.EditText;


public class HelloWorld2Activity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
      
        
        /*button*/
        Button btn=(Button)findViewById(R.id.btn);
        btn.setOnClickListener ( new View.OnClickListener() 
        {
             
public void onClick(View v) {
EditText edt= (EditText)HelloWorld2Activity.this.findViewById(R.id.edt);
TextView txt= (TextView)HelloWorld2Activity.this.findViewById(R.id.txt);
txt.setText(getString(R.string.msg_dialog)+edt.getText());

}
});//end of btn.setOnClickListener
        
    }

}

=============main.xml=======

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >




    <TextView
        android:id="@+id/txt"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/hello" />






    <Button
        android:id="@+id/btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/go" />








    <EditText
        android:id="@+id/edt"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:inputType="numberPassword" >


        <requestFocus />


    </EditText>


</LinearLayout>

==========strings.xml================

<?xml version="1.0" encoding="utf-8"?>
<resources>


    <string name="hello">Hello World, HelloWorld2!</string>
    <string name="app_name">Button</string>
    <string name="tit_dialog">提示</string>
    <string name="msg_dialog">你好，中国</string>
    <string name="ok_dialog">确定</string>
    <string name="go">浏览</string>


</resources>