Using a logo instead of an icon
By default, the system uses your application icon in the action bar, as specified by the icon attribute in the<application> or <activity> element. However, if you also specify the logo attribute, then the action bar uses the logo image instead of the icon.
A logo should usually be wider than the icon, but should not include unnecessary text. You should generally 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 logo represents the expected user brand, whereas the app's icon is a modified version that conforms to the square requirement for the launcher icon.
如果在minifest.xml中指定了logo,ActionBar就不用icon而用它.
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:logo="@drawable/ab_me_l"
android:label="@string/app_name"
android:theme="@style/AppBaseTheme" > ...