在android ADT 16.0以后控件中没有文本描述的view如果不加android:contentDescription="@string/**"就会有黄色的下划线。
而android:contentDescription的属性作用是：设置View的备注说明，作为一种辅助功能提供，为一些没有文字描述的View提供说明，如ImageButton。这里在界面上不会有效果，自己在程序中控制，可临时放一点字符串数据，或者文字描述为null，如：android:contentDescription=" ".
api文档中解释：
Resolved this warning by setting attribute android:contentDescription for my ImageView
android:contentDescription="@string/desc"
Android Lint support in ADT 16 throws this warning to ensure that image widgets provide a contentDescription
This defines text that briefly describes content of the view. This property is used primarily for accessibility. Since some views do not have textual representation this attribute can be used for providing such.
Non-textual widgets like ImageViews and ImageButtons should use the contentDescription attribute to specify a textual description of the widget such that screen readers and other accessibility tools can adequately describe the user interface.
