Android的xml文件中的@和?的区别
4381 点击·0 回帖
灯火互联
楼主
 |  | |
 | @大家已经司空见惯。比如@+id/... @string/... 看下面代码： [html] <ProgressBar android:id="@+id/firstProgressBar" style="?android:progressBarStyleHorizontal" android:layout_width="200dp" android:layout_height="wrap_content" android:visibility="gone" /> <ProgressBar android:id="@+id/firstProgressBar" style="?android:progressBarStyleHorizontal" android:layout_width="200dp" android:layout_height="wrap_content" android:visibility="gone" /> 上面代码中用到了“？”，那么“？”是什么意思呢？ “？”引用主题属性，当您使用这个标记，你所提供的资源名必须能够在主题属性中找到，因为资源工具认为这个资源属性是被期望得到的，您不需要明确的指出它的类型（也就是不需要写全在哪个文件中?android:attr/android:textDisabledColor） 那么什么又叫主题属性呢？ 你可以在Android的SDK的以下目录中找到attrs.xml文件 D:\android-sdk\platforms\android-16\data\res\values 打开这个文件可以看到，Android系统的属性都定义在这个文件中。 举个例子（ImageView）： [html] <declare-styleable name="ImageView"> <!-- Sets a drawable as the content of this ImageView. --> <attr name="src" format="reference|color" /> <!-- Controls how the image should be resized or moved to match the size of this ImageView. --> <attr name="scaleType"> <enum name="matrix" value="0" /> <enum name="fitXY" value="1" /> <enum name="fitStart" value="2" /> <enum name="fitCenter" value="3" /> <enum name="fitEnd" value="4" /> <enum name="center" value="5" /> <enum name="centerCrop" value="6" /> <enum name="centerInside" value="7" /> </attr> <!-- Set this to true if you want the ImageView to adjust its bounds to preserve the aspect ratio of its drawable. --> <attr name="adjustViewBounds" format="boolean" /> <!-- An optional argument to supply a maximum width for this view. See {see android.widget.ImageView#setMaxWidth} for details. --> <attr name="maxWidth" format="dimension" /> <!-- An optional argument to supply a maximum height for this view. See {see android.widget.ImageView#setMaxHeight} for details. --> <attr name="maxHeight" format="dimension" /> <!-- Set a tinting color for the image --> <attr name="tint" format="color" /> <!-- If true, the image view will be baseline aligned with based on its bottom edge --> <attr name="baselineAlignBottom" format="boolean" /> <!-- If true, the image will be cropped to fit within its padding --> <attr name="cropToPadding" format="boolean" /> </declare-styleable> <declare-styleable name="ImageView"> <!-- Sets a drawable as the content of this ImageView. --> <attr name="src" format="reference|color" /> <!-- Controls how the image should be resized or moved to match the size of this ImageView. --> <attr name="scaleType"> <enum name="matrix" value="0" /> <enum name="fitXY" value="1" /> <enum name="fitStart" value="2" /> <enum name="fitCenter" value="3" /> <enum name="fitEnd" value="4" /> <enum name="center" value="5" /> <enum name="centerCrop" value="6" /> <enum name="centerInside" value="7" /> </attr> <!-- Set this to true if you want the ImageView to adjust its bounds to preserve the aspect ratio of its drawable. --> <attr name="adjustViewBounds" format="boolean" /> <!-- An optional argument to supply a maximum width for this view. See {see android.widget.ImageView#setMaxWidth} for details. --> <attr name="maxWidth" format="dimension" /> <!-- An optional argument to supply a maximum height for this view. See {see android.widget.ImageView#setMaxHeight} for details. --> <attr name="maxHeight" format="dimension" /> <!-- Set a tinting color for the image --> <attr name="tint" format="color" /> <!-- If true, the image view will be baseline aligned with based on its bottom edge --> <attr name="baselineAlignBottom" format="boolean" /> <!-- If true, the image will be cropped to fit within its padding --> <attr name="cropToPadding" format="boolean" /> </declare-styleable> 以上是从attrs.xml文件中提取的，可以看到ImageView的一些特有属性（由于ImageView继承自View，所以View的属性自然就继承了）。 同样，Android系统也为Theme定义了很多属性（可以看看attrs.xml文件），其中每个主题属性的名称都一一对应D:\android-sdk\platforms\android-16\data\res\values目录下的themes.xml文件。当要用到主题属性的时候，就不需要特别指定android:attr/，可以直接在？后面加上属性名。 | |
 |  |