学步园

public class ExitUtil {
public static final int EXIT_APPLICATION = 0x0001;
private Context mContext;
public ExitUtil(Context context) {
mContext = context;
}
// 完全退出应用程序
public void exit() {
Intent intent = new Intent(mContext, MainActivity.class);
// 设置FLAG!!!表示从当前Activity跳转到intent构造方法中添加的类，并且把两个Activity之间的Activity给finish掉！
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
// 发出退出应用程序指示
intent.putExtra("flag", EXIT_APPLICATION);
mContext.startActivity(intent);
}
}

public class BActivity extends Activity {
private static final int MENU_EXITAPPLICATION = Menu.FIRST;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
TextView tv = new TextView(this);
tv.setText("wecolme!");
setContentView(tv);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
menu.add(0, MENU_EXITAPPLICATION, 0, "退出程序");
return super.onCreateOptionsMenu(menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// 其它Activity调用程序就通过此方法
if (item.getItemId() == MENU_EXITAPPLICATION) {
ExitUtil eu = new ExitUtil(this);
eu.exit();
}
return super.onOptionsItemSelected(item);
}
}

public class MainActivity extends Activity {
Button btn = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btn = (Button) findViewById(R.id.btn);
btn.setOnClickListener(new OnClickListener() {// 点击进入BActivity
@Override
public void onClick(View v) {
Intent intent = new Intent(getApplicationContext(), BActivity.class);
startActivity(intent);
}
});
}
// 接受退出程序的指令
@Override
protected void onStart() {
int flag = getIntent().getIntExtra("flag", 0);// 第一次,进入应用时获取得到的flag为默认的值0!
if (flag == ExitUtil.EXIT_APPLICATION) {
finish();
}
Log.i("TAG", "Start");
super.onStart();
}
// 当Activity是单例模式的时候，两次启动该Activity就不会调用onCreate->onStart这些方法了
@Override
protected void onNewIntent(Intent intent) {
int flag = getIntent().getIntExtra("flag", 0);
if (flag == ExitUtil.EXIT_APPLICATION) {
finish();
}
Log.i("TAG", "NewIntent");
super.onNewIntent(intent);
}
}