<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:orientation="vertical"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:paddingBottom="@dimen/activity_vertical_margin"    android:paddingLeft="@dimen/activity_horizontal_margin"    android:paddingRight="@dimen/activity_horizontal_margin"    android:paddingTop="@dimen/activity_vertical_margin"    tools:context=".MainActivity" >    <TextView         android:id="@+id/show"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="@string/hello_world" />    <Button         android:id="@+id/ok"         android:text="单击我"        android:layout_width="wrap_content"        android:layout_height="wrap_content"/></RelativeLayout>

package com.example.test;import java.util.Date;import android.os.Bundle;import android.app.Activity;import android.view.Menu;import android.view.View;import android.widget.Button;import android.widget.TextView;public class MainActivity extends Activity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        Button bn=(Button)findViewById(R.id.ok);        bn.setOnClickListener(new View.OnClickListener()        {            public void onClick(View v)            {                final TextView show=(TextView)findViewById(R.id.show);                show.setText("Hello Android~"+new Date());            }        });    }    @Override    public boolean onCreateOptionsMenu(Menu menu) {        // Inflate the menu; this adds items to the action bar if it is present.        getMenuInflater().inflate(R.menu.main, menu);        return true;    }    }