后退按钮表示像刷新键

Question

当我在测试我的应用程序时单击后退按钮时，它会刷新相同的活动，而不是返回到上一个活动。视频开始然后停止并告诉我“不能播放此视频” 以下是第一个和第二个活动代码：

import android.app.Activity;
public class Help extends Activity {

CheckBox c[] = new CheckBox[21];
private Button btn;


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

    btn = (Button)findViewById(R.id.submit);
    c[0]= (CheckBox) findViewById(R.id.bulk);
    c[1]= (CheckBox) findViewById(R.id.cond);


import android.app.Activity;
public class Med extends Activity {
VideoView vid;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
    setContentView(R.layout.med);
    vid = (VideoView)findViewById(R.id.setups); 
    String urlpath = "android.resource://" + getPackageName() + "/" + R.raw.setups;
    vid.setVideoURI(Uri.parse(urlpath));
    vid.start()