theme- 工作原理

首先看一下theme中的设置，代码如下

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <style name="Theme.Funui" parent="Theme.Holo.Light">
        <item name="isFunui">true</item>
        <item name="colorForeground">@android:color/bright_foreground_funui</item>
        <item name="colorForegroundInverse">@android:color/bright_foreground_funui_inverse</item>
        <item name="colorBackground">@android:color/background_funui</item>
        <item name="colorBackgroundCacheHint">@android:drawable/background_cache_hint_selector_funui</item>
        <item name="disabledAlpha">0.5</item>
        <item name="backgroundDimAmount">0.6</item>

        <item name="colorPressedHighlight">@color/funui_gray_light</item>
        <item name="colorLongPressedHighlight">@color/funui_gray_bright</item>
        <item name="colorFocusedHighlight">@color/funui_blue_dark</item>
        <item name="colorMultiSelectHighlight">@color/funui_green_light</item>
        <item name="colorActivatedHighlight">@color/funui_blue_dark</item>

        <!-- Text styles -->
        <item name="textAppearance">@android:style/TextAppearance.Funui</item>
        <item name="textAppearanceInverse">@android:style/TextAppearance.Funui.Inverse</item>

        <item name="textColorPrimary">@android:color/primary_text_funui</item>
        <item name="textColorSecondary">@android:color/secondary_text_funui</item>
        <item name="textColorTertiary">@android:color/tertiary_text_funui</item>
        <item name="textColorPrimaryInverse">@android:color/primary_text_funui_inverse</item>
        <item name="textColorSecondaryInverse">@android:color/secondary_text_funui_inverse</item>
        <item name="textColorTertiaryInverse">@android:color/tertiary_text_funui_inverse</item>
        <item name="textColorPrimaryDisableOnly">@android:color/primary_text_disable_only_funui</item>
        <item name="textColorPrimaryInverseDisableOnly">@android:color/primary_text_disable_only_funui_inverse</item>
        <item name="textColorPrimaryNoDisable">@android:color/primary_text_nodisable_funui</item>
        <item name="textColorSecondaryNoDisable">@android:color/secondary_text_nodisable_funui</item>
        <item name="textColorPrimaryInverseNoDisable">@android:color/primary_text_nodisable_funui_inverse</item>
        <item name="textColorSecondaryInverseNoDisable">@android:color/secondary_text_nodisable_funui_inverse</item>
        <item name="textColorHint">@android:color/hint_foreground_funui</item>
        <item name="textColorHintInverse">@android:color/hint_foreground_funui_inverse</item>
        <item name="textColorSearchUrl">@android:color/search_url_text_funui</item>
        <item name="textColorHighlight">@android:color/highlighted_text_funui</item>
        <item name="textColorHighlightInverse">@android:color/highlighted_text_funui_inverse</item>
        <item name="textColorLink">@android:color/funui_blue_light</item>
        <item name="textColorLinkInverse">@android:color/funui_blue_light</item>
        <item name="textColorAlertDialogListItem">@android:color/primary_text_funui</item>
　　　　　<item name="checkboxStyle">@android:style/Widget.Funui.CompoundButton.CheckBox</item>
         <item name="searchViewTextColor">@color/searchview_text_color</item>
        <item name="textAppearanceLarge">@android:style/TextAppearance.Funui.Large</item>
        <item name="textAppearanceMedium">@android:style/TextAppearance.Funui.Medium</item>
        <item name="textAppearanceSmall">@android:style/TextAppearance.Funui.Small</item>
        <item name="textAppearanceLargeInverse">@android:style/TextAppearance.Funui.Large.Inverse</item>
        <item name="textAppearanceMediumInverse">@android:style/TextAppearance.Funui.Medium.Inverse</item>

</Resources>

然后我们查找一下其中的一个属性<item name="checkboxStyle">@android:style/Widget.Funui.CompoundButton.CheckBox</item>

我们先不说后面的@android:style/Widget.Funui.CompoundButton.CheckBox 就先看一下这个checkboxStyle ，搜索以后，发现如下代码

public class Button extends TextView {
    public Button(Context context) {
        this(context, null);
    }   

    public Button(Context context, AttributeSet attrs) {

//引用的地方
        this(context, attrs, com.android.internal.R.attr.buttonStyle);
    }   

    public Button(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }   

    @Override
    public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
        super.onInitializeAccessibilityEvent(event);
        event.setClassName(Button.class.getName());
    }   

    @Override
    public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
        super.onInitializeAccessibilityNodeInfo(info);
        info.setClassName(Button.class.getName());
    }
}

这就是第一种情况，也就是，属性是直接在代码中添加的，有点类似于我们的自定义属性。不过呢，这个明显的是，直接添加的一个theme,他的作用就跟我们直接创建一个aaa的style，然后new (.....,R.style.aaa)一样的，

只不过它是应用整个activity的

另外我们还发现了它出现在另外一个地方res/values/attr.xml中，如下

<!--类似于一个声明-->
<attr name="checkboxStyle" format="reference" />
        <!-- Default CheckedTextView style. -->
        <attr name="checkedTextViewStyle" format="reference" />
        <!-- Default ListView style for drop downs. -->
        <attr name="dropDownListViewStyle" format="reference" />
        <!-- Default EditText style. -->
        <attr name="editTextStyle" format="reference" />
        <!-- Default ExpandableListView style. -->
        <attr name="expandableListViewStyle" format="reference" />
        <!-- ExpandableListView with white background. -->
        <attr name="expandableListViewWhiteStyle" format="reference" />
        <!-- Default Gallery style. -->
        <attr name="galleryStyle" format="reference" />
        <!-- Default GestureOverlayView style. -->
        <attr name="gestureOverlayViewStyle" format="reference" />
        <!-- Default GridView style. -->
        <attr name="gridViewStyle" format="reference" />
        <!-- The style resource to use for an ImageButton. -->
        <attr name="imageButtonStyle" format="reference" />
        <!-- The style resource to use for an ImageButton that is an image well. -->
        <attr name="imageWellStyle" format="reference" />
        <!-- Default ListView style. -->
        <attr name="listViewStyle" format="reference" />

至于它后面跟的数值Widget.Funui.CompoundButton.CheckBox，如下

 <style name="Widget.CompoundButton.CheckBox">
        <item name="android:button">?android:attr/listChoiceIndicatorMultiple</item>
    </style>

我们可以看到，它其实就是一个checkbox 中button属性的设置

下面我们来查找另外的一个属性看看结果<item name="searchViewTextColor">@color/searchview_text_color</item>

仍然是在res/values/attr.xml里面看到它的身影

<attr name="searchViewTextColor" format="reference|color" />

另外，并没有在代码中看到它，只是在一些xml中看到了，如下

 <view class="android.widget.SearchView$SearchAutoComplete"
                android:id="@+id/search_src_text"
                android:layout_height="36dip"
                android:layout_width="0dp"
                android:layout_weight="1"
                android:minWidth="@dimen/search_view_text_min_width"
                android:layout_gravity="center_vertical"
                android:paddingStart="@dimen/dropdownitem_text_padding_left"
                android:paddingEnd="@dimen/dropdownitem_text_padding_right"
                android:singleLine="true"
                android:ellipsize="end"
                android:background="@null"
                android:inputType="text|textAutoComplete|textNoSuggestions"
                android:textColor="?android:attr/searchViewTextColor"
                android:textColorHint="?android:attr/searchViewTextColorHint"
                android:imeOptions="actionSearch"
                android:dropDownHeight="wrap_content"
                android:dropDownAnchor="@id/search_edit_frame"
                android:dropDownVerticalOffset="0dip"
                android:dropDownHorizontalOffset="0dip"
                android:contentDescription="@string/searchview_description_query"
            />

android:textColor="?android:attr/searchViewTextColor"
它是引用了

searchViewTextColor 这个值在theme有了定义，相当于引用了@color/searchview_text_color

这里我们是不是可以得出一个结论呢，
theme下定义的资源，我们都是可以直接使用的，也就是它就是一个资源的别名，就像定义在value中一样。
不同的是，它是可以被覆盖的，也就是说，当前应用会覆盖系统默认的