context.obtainStyledAttributes 研究

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我们在自定义View 时,一般都会用到 

TypedArray obtainStyledAttributes(                AttributeSet set, int[] attrs, int defStyleAttr, int defStyleRes);

 对于它的前面2个参数可能大家都知道, 对于后面两个参数一直不明白怎么用。

于是今天查了下。

           context obtainStyledAttributes 最终会调到Resources.Theme.obtainStyledAttributes(AttributeSet set,
                int[] attrs, int defStyleAttr, int defStyleRes) 

再看一下参数解释:

         * @param set The base set of attribute values.  May be null.
         * @param attrs The desired attributes to be retrieved.
         * @param defStyleAttr An attribute in the current theme that contains a
         *                     reference to a style resource that supplies
         *                     defaults values for the TypedArray.  Can be
         *                     0 to not look for defaults.
         * @param defStyleRes A resource identifier of a style resource that
         *                    supplies default values for the TypedArray,
         *                    used only if defStyleAttr is 0 or can not be found
         *                    in the theme.  Can be 0 to not look for defaults.


defStyleAttr 指向当前theme 某个item 描述的style 该style指定了一些默认值为这个TypedArray

defStyleRes  当defStyleAttr 找不到或者为0, 可以直接指定某个style


不是很理解 ,搜了一下源码:

发现用的地方 不多。如CalendarView

ypedArray attributesArray = context.obtainStyledAttributes(attrs, R.styleable.CalendarView,                R.attr.calendarViewStyle, 0);
CalendarView  在 attrs.xml 中 定义如下:

<declare-styleable name="CalendarView">        <!-- The first day of week according to {@link Java.util.Calendar}. -->        <attr name="firstDayOfWeek" format="integer" />        <!-- Whether do show week numbers. -->        <attr name="showWeekNumber" format="boolean" />        <!-- The minimal date shown by this calendar view in mm/dd/yyyy format. -->        <attr name="minDate" />        <!-- The minimal date shown by this calendar view in mm/dd/yyyy format. -->        <attr name="maxDate" />        <!-- The number of weeks to be shown. -->        <attr name="shownWeekCount" format="integer"/>        <!-- The background color for the selected week. -->        <attr name="selectedWeekBackgroundColor" format="color|reference" />        <!-- The color for the dates of the focused month. -->        <attr name="focusedMonthDateColor" format="color|reference" />        <!-- The color for the dates of an unfocused month. -->        <attr name="unfocusedMonthDateColor" format="color|reference" />        <!-- The color for the week numbers. -->        <attr name="weekNumberColor" format="color|reference" />        <!-- The color for the separator line between weeks. -->        <attr name="weekSeparatorLineColor" format="color|reference" />        <!-- Drawable for the vertical bar shown at the beginning and at the end of the selected date. -->        <attr name="selectedDateVerticalBar" format="reference" />        <!-- The text appearance for the week day abbreviation of the calendar header. -->        <attr name="weekDayTextAppearance" format="reference" />        <!-- The text appearance for the calendar dates. -->        <attr name="dateTextAppearance" format="reference" />    </declare-styleable>

默认 defStyleAttr 为 calendarViewStyle 

也定义在attrs.xml

       

 <!-- The CalendarView style. -->        <attr name="calendarViewStyle" format="reference" />

再看看在theme.xml 中 它指向:

<!-- CalendarView style--Defalut>        <item name="calendarViewStyle">@style/Widget.CalendarView</item>        。。。。           <!-- CalendarView style--Holo>        <item name="calendarViewStyle">@style/Widget.Holo.CalendarView</item>        。。。         <!-- CalendarView style-HOLOLight->        <item name="calendarViewStyle">@style/Widget.Holo.Light.CalendarView</item>

不同的theme 指向不同的style


 如style.xml 中的


 <style name="Widget.CalendarView">        <item name="Android:showWeekNumber">true</item>        <item name="android:minDate">01/01/1900</item>        <item name="android:maxDate">12/31/2100</item>        <item name="android:shownWeekCount">6</item>        <item name="android:selectedWeekBackgroundColor">#330099FF</item>        <item name="android:focusedMonthDateColor">#FFFFFFFF</item>        <item name="android:unfocusedMonthDateColor">#66FFFFFF</item>        <item name="android:weekNumberColor">#33FFFFFF</item>        <item name="android:weekSeparatorLineColor">#19FFFFFF</item>        <item name="android:selectedDateVerticalBar">@android:drawable/day_picker_week_view_dayline_holo</item>        <item name="android:weekDayTextAppearance">@android:style/TextAppearance.Small.CalendarViewWeekDayView</item>        <item name="android:dateTextAppearance">?android:attr/textAppearanceSmall</item>    </style>

指定了CalendarView 的atrrs 中的一些默认值。


自此我们明白了defStyleAttr的用法。 如果某个stylable 定义了一些item , 但是使用者并不一定对所有的item 在xml 使用时设置。 我们需要给他设定一些默认值

这些值可以在不同的theme 中不一样。


defStyleRes 使用则更简单。可以直接某个style, 当defStyleAttr不起作用时。


转自:http://blog.csdn.net/yunnywu/article/details/23694341
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