activity_main.xml檔案中

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    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="com.t20.getVersion.MainActivity" >
	
    <!-- 獲得當前作業系統的版本號 -->
    <Button
        android:id="@+id/btnGetVersion"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="15dp"
        android:text="獲得版本號" 
        android:onClick="getVersion"/>

    <TextView
        android:id="@+id/tvgetVersion"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/btnGetVersion"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="40dp"
        android:text="" />

</RelativeLayout>
 

MainActivity.java檔案中

package com.t20.getVersion;

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

public class MainActivity extends Activity {
	private TextView tvGetVersion;

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

		// 獲取控制元件
		tvGetVersion = (TextView) findViewById(R.id.tvgetVersion);
	}

	/**
	 * 獲得版本號
	 * 
	 * @param v
	 */
	public void getVersion(View v) {
		String version = Build.VERSION.SDK_INT + "";
		tvGetVersion.setText("當前作業系統的版本號為：" + version);
	}
}