<uses-sdkandroid:minSdkVersion="18"android:targetSdkVersion="18" />

<itemandroid:id="@+id/item1"android:alphabeticShortcut="B"android:orderInCategory="200"android:title="返回"></item><itemandroid:id="@+id/help"android:title="帮助"android:showAsAction="always"/><itemandroid:id="@+id/about"android:title="关于"android:showAsAction="always"/><itemandroid:id="@+id/clock"android:title="时钟"android:showAsAction="always"android:actionLayout="@layout/clock"/>

public boolean onCreateOptionsMenu(Menu menu) {// TODO Auto-generated method stubMenuInflater inflater = new MenuInflater(this);inflater.inflate(R.menu.main, menu);return super.onCreateOptionsMenu(menu);}public boolean onOptionsItemSelected(MenuItem item) {// TODO Auto-generated method stubswitch (item.getItemId()) {case android.R.id.home://创建启动MainActivity的IntentIntent intent=new Intent(this,MainActivity.class);//添加额外的Flag，将Activity栈中处于MainActivity之上的Activity弹出
   intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);startActivity(intent);break;case R.id.help:Intent intent1=new Intent(this,HelpActivity.class);startActivity(intent1);break;default:break;}return super.onOptionsItemSelected(item);}

ActionBar actionBar = getActionBar();//获取ActionBar对象actionBar.setDisplayShowHomeEnabled(true);//显示应用程序图标actionBar.setDisplayHomeAsUpEnabled(true);//将应用程序图标转变为可点击图标，并添加一个返回箭头。

@OverridePublic Boolean onOptionsItemSelected(MenuItem item) {// TODO Auto-generated method stubswitch (item.getItemId()) {case android.R.id.home://创建启动MainActivity的IntentIntent intent=new Intent(this,MainActivity.class);//添加额外的Flag，将Activity栈中处于MainActivity之上的Activity弹出
            intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);startActivity(intent);break;default:break;}returnsuper.onOptionsItemSelected(item);}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical" ><AnalogClockandroid:id="@+id/analogClock1"android:layout_width="wrap_content"android:layout_height="wrap_content" /></LinearLayout>

 <itemandroid:id="@+id/clock"android:title="时钟"android:showAsAction="always"android:actionLayout="@layout/clock"/>