Android icon vs logo

Android 配置文件中有icon和logo两个属性。那这两个属性有什么区别呢？
清单文件中activity的icon属性介绍：

android:icon
An icon representing the activity. The icon is displayed to users when a representation of the activity is required on-screen. For example, icons for activities that initiate tasks are displayed in the launcher window. The icon is often accompaniedby
a label (see the android:label attribute).
This attribute must be set as a reference to a drawable resource containing theimage definition. If it is not set, the icon specified for the application as awhole is used instead (see the <application>element's icon attribute).
Theactivity's icon — whether set here or by the <application> element— is also the default
icon for all the activity's intent filters (see the <intent-filter> element's icon attribute).

大体意思就是说icon代表了一个activity，它作为activity的界面显示展示给用户，比如说启动界面上MainActivity的图标。此外，它的属性值必须是一个drawable类型的资源文件。如果没有给activity定义，那么这个activity会使用application的icon属性。
下面是application的icon属性介绍：

android:icon
An iconfor the application as whole, and the default icon for each of theapplication's components. See the individual icon attributesfor <activity>, <activity-alias>, <service>, <receiver>,and <provider>elements.
This attribute must be set as a reference to a drawable resource containing the image (for example"@drawable/icon").There is no default icon.
同activity的icon属性类似，但是application的icon属性石没有默认值的。aplication的icon属性是用来显示在安装界面和安装包缩略图的，而不包括桌面和启动器图标。桌面、启动器上显示的图是应用的主activity（一般名称为MainActivity）里icon。
logo属性介绍：

android:logo
A logo for the application as whole, and the default logofor activities.
This attribute must be set as a reference to a drawableresource containing the image (for example"@drawable/logo"). There is no default logo.

logo不会被作为桌面图标，仅作为activity的导航图，而当同时设置了icon与logo属性时（闲的），logo会完全覆盖掉icon。

Using a logo instead ofan icon

By default, the systemuses your application icon in the action bar, as specified by the icon attribute
in the<application> or <activity> element.
However, if you also specifythe logo attribute, then the action bar usesthe logo image
instead of the icon.
A logo should usually bewider than the icon, but should not include unnecessary text. You shouldgenerally use a logo only when it represents your brand in a traditional format that users recognize. A good example is the YouTube
app's logo—the logorepresents the expected user brand, whereas the app's icon is a modifiedversion that conforms to the square requirement for the launcher icon.

ActionBar的应用：

ActionBar actionBar=getActionBar();

使用android:logo属性。不像方方正正的icon，logo的图像不会有任何宽度限制
当你有Logo的时候，你可以隐藏label。

隐藏Label标签：

actionBar.setDisplayShowTitleEnabled(false);

隐藏logo和icon：

actionBar.setDisplayShowHomeEnabled(false);

默认情况下，actionBar放在你的activity的顶部，且作为activity布局的一部分。设置成为覆盖模式后，actionBar相当于漂浮在activity之上，不干预activity的布局。

public void onCreate(Bundle savedInstanceState) { 
   super.onCreate(savedInstanceState);
   getWindow().requestFeature(Window.FEATURE_ACTION_BAR_OVERLAY);
   setContentView(R.layout.main);
}

参考：
http://stackoverflow.com/questions/6735649/android-icon-vs-logo
http://tieba.baidu.com/p/3516704970 http://blog.csdn.net/jdsjlzx/article/details/41353029