Android View(4)-View関連プロパティの詳細

A collection of attributes, as found associated with a tag in an XML document.
 Often you will not want to use this interface directly, instead passing it to Resources.
 Theme.obtainStyledAttributes() which will take care of parsing the attributes for you. 
 In particular, the Resources API will convert resource references 
 (attribute values such as "@string/my_label" in the original XML) to the desired type for you; 
 if you use AttributeSet directly then you will need to manually check for resource references 
 (with getAttributeResourceValue(int, int)) and do the resource lookup yourself if needed.
 Direct use of AttributeSet also prevents the application of themes and styles when retrieving attribute values.

This interface provides an efficient mechanism for retrieving data from compiled XML files, 
 which can be retrieved for a particular XmlPullParser through Xml.asAttributeSet(). 
 Normally this will return an implementation of the interface that works on top of 
 a generic XmlPullParser, however it is more useful in conjunction with compiled XML resources:
 XmlPullParser parser = resources.getXml(myResource);
 AttributeSet attributes = Xml.asAttributeSet(parser);

The implementation returned here, unlike using the implementation on top of a generic XmlPullParser, 
is highly optimized by retrieving pre-computed information that was generated by aapt 
when compiling your resources. For example, the getAttributeFloatValue(int, float)
 method returns a floating point number previous stored in the compiled resource 
 instead of parsing at runtime the string originally in the XML file.

This interface also provides additional information contained in the 
compiled XML resource that is not available in a normal XML file, 
such as getAttributeNameResource(int) which returns the resource 
identifier associated with a particular XML attribute name.

public interface AttributeSet {
    /**
     * Returns the number of attributes available in the set.
     * 
     * @return A positive integer, or 0 if the set is empty.
     */
    public int getAttributeCount();
    ...
    /**
     * Return the integer value of attribute at 'index' that is formatted as an
     * unsigned value.  In particular, the formats 0xn...n and #n...n are
     * handled.
     * 
     * @param index Index of the desired attribute, 0...count-1.
     * @param defaultValue What to return if the attribute isn't found.
     * 
     * @return Resulting value.
     */
    public int getAttributeUnsignedIntValue(int index, int defaultValue);
    /**
     * Return the float value of attribute at 'index'.
     * 
     * @param index Index of the desired attribute, 0...count-1.
     * @param defaultValue What to return if the attribute isn't found.
     * 
     * @return Resulting value.
     */
    public float getAttributeFloatValue(int index, float defaultValue);

    /**
     * Return the value of the "id" attribute or null if there is not one.
     * Equivalent to getAttributeValue(null, "id").
     * 
     * @return The id attribute's value or null.
     */
    public String getIdAttribute();
    /**
     * Return the value of the "class" attribute or null if there is not one.
     * Equivalent to getAttributeValue(null, "class").
     * 
     * @return The class attribute's value or null.
     */
    public String getClassAttribute();

    ...
}

XmlPullParser parser = resources.getXml(myResource);
 AttributeSet attributes = Xml.asAttributeSet(parser);

 public static AttributeSet asAttributeSet(XmlPullParser parser) {
        return (parser instanceof AttributeSet)
                ? (AttributeSet) parser
                : new XmlPullAttributes(parser);
    }

class XmlPullAttributes implements AttributeSet {
    public XmlPullAttributes(XmlPullParser parser) {
        mParser = parser;
    }
    public int getAttributeCount() {
        return mParser.getAttributeCount();
    }

    public String getAttributeName(int index) {
        return mParser.getAttributeName(index);
    }

    public String getAttributeValue(int index) {
        return mParser.getAttributeValue(index);
    }

    public String getAttributeValue(String namespace, String name) {
        return mParser.getAttributeValue(namespace, name);
    }

    public String getPositionDescription() {
        return mParser.getPositionDescription();
    }
    ...
    /*package*/ XmlPullParser mParser;
}

Container for an array of values that were retrieved with 
obtainStyledAttributes(AttributeSet, int[], int, int) or obtainAttributes(AttributeSet, int[]). 
Be sure to call recycle() when done with them. The indices used to retrieve values from this
structure correspond to the positions of the attributes given to obtainStyledAttributes.

public class TypedArray {

private final Resources mResources;
    /*package*/ XmlBlock.Parser mXml;
    /*package*/ int[] mRsrcs;
    /*package*/ int[] mData;
    /*package*/ int[] mIndices;
    /*package*/ int mLength;
    /*package*/ TypedValue mValue = new TypedValue();
  /**
     * Return the number of values in this array.
     */
    public int length() {
        return mLength;
    }
    
    /**
     * Return the number of indices in the array that actually have data.
     */
    public int getIndexCount() {
        return mIndices[0];
    }
    
    /**
     * Return an index in the array that has data.
     * 
     * @param at The index you would like to returned, ranging from 0 to
     * {@link #getIndexCount()}.
     * 
     * @return The index at the given offset, which can be used with
     * {@link #getValue} and related APIs.
     */
    public int getIndex(int at) {
        return mIndices[1+at];
    }
...
}

 To define custom attributes, add <declare-styleable> resources to your project.
 It's customary to put these resources into a res/values/attrs.xml file. 
 Here's an example of an attrs.xml file:

<resources>
   <declare-styleable name="PieChart">
       <attr name="showText" format="boolean" />
       <attr name="labelPosition" format="enum">
           <enum name="left" value="0"/>
           <enum name="right" value="1"/>
       </attr>
   </declare-styleable>
</resources>
This code declares two custom attributes, showText and labelPosition, that belong to 
a styleable entity named PieChart. The name of the styleable entity is, 
by convention, the same name as the name of the class that defines the custom view.
 Although it's not strictly necessary to follow this convention, many popular 
 code editors depend on this naming convention to provide statement completion.

        <declare-styleable name="TextView">
        ...
        <!-- Text color. -->
        <attr name="textColor" />
        <!-- Color of the text selection highlight. -->
        <attr name="textColorHighlight" />
        <!-- Color of the hint text. -->
        <attr name="textColorHint" />
        <!-- Base text color, typeface, size, and style. -->
        <attr name="textAppearance" />
        <!-- Size of the text. Recommended dimension type for text is "sp" for scaled-pixels (example: 15sp). -->
        <attr name="textSize" />
        <!-- Sets the horizontal scaling factor for the text. -->
        <attr name="textScaleX" format="float" />
        <!-- Typeface (normal, sans, serif, monospace) for the text. -->
        <attr name="typeface" />
        <!-- Style (bold, italic, bolditalic) for the text. -->
        <attr name="textStyle" />
        <!-- Text color for links. -->
        <attr name="textColorLink" />
        <!-- Makes the cursor visible (the default) or invisible. -->
        <attr name="cursorVisible" format="boolean" />
        <!-- Makes the TextView be at most this many lines tall. -->
        <attr name="maxLines" format="integer" min="0" />
        <!-- Makes the TextView be at most this many pixels tall. -->
        <attr name="maxHeight" />
        <!-- Makes the TextView be exactly this many lines tall. -->
        <attr name="lines" format="integer" min="0" />
        <!-- Makes the TextView be exactly this many pixels tall.
             You could get the same effect by specifying this number in the
             layout parameters. -->
        <attr name="height" format="dimension" />
        <!-- Makes the TextView be at least this many lines tall. -->
        <attr name="minLines" format="integer" min="0" />
        <!-- Makes the TextView be at least this many pixels tall. -->
        <attr name="minHeight" />
        <!-- Makes the TextView be at most this many ems wide. -->
        <attr name="maxEms" format="integer" min="0" />
        <!-- Makes the TextView be at most this many pixels wide. -->
        <attr name="maxWidth" />
        <!-- Makes the TextView be exactly this many ems wide. -->
        <attr name="ems" format="integer" min="0" />
        <!-- Makes the TextView be exactly this many pixels wide.
             You could get the same effect by specifying this number in the
             layout parameters. -->
        <attr name="width" format="dimension" />
        <!-- Makes the TextView be at least this many ems wide. -->
        <attr name="minEms" format="integer" min="0" />
        <!-- Makes the TextView be at least this many pixels wide. -->
        <attr name="minWidth" />
        ...
    </declare-styleable>
	 <declare-styleable name="TextViewAppearance">
        <!-- Base text color, typeface, size, and style. -->
        <attr name="textAppearance" />
    </declare-styleable>
	...

1. reference：    。
2. color：   。
3. boolean：   。
4. dimension：   。
5. float：   。
6. integer：   。
7. string：   。
8. fraction：   。
9. enum：   。
10. flag：    。

public class TextView extends View implements ViewTreeObserver.OnPreDrawListener {
        ...
        public TextView(Context context,
                    AttributeSet attrs,
                    int defStyle) {
        super(context, attrs, defStyle);
         ...
         //   View   
        final Resources.Theme theme = context.getTheme();
        /*
         * Look the appearance up without checking first if it exists because
         * almost every TextView has one and it greatly simplifies the logic
         * to be able to parse the appearance first and then let specific tags
         * for this View override it.
         */
        //       ，  obtainStyledAttributes  TypedArray 
        TypedArray a = theme.obtainStyledAttributes(
                    attrs, com.android.internal.R.styleable.TextViewAppearance, defStyle, 0);
        TypedArray appearance = null;
		//  index       
        int ap = a.getResourceId(
                com.android.internal.R.styleable.TextViewAppearance_textAppearance, -1);
        a.recycle();//    ，  recycle（）
        if (ap != -1) {
		//       TextView       
            appearance = theme.obtainStyledAttributes(
                    ap, com.android.internal.R.styleable.TextAppearance);
        }
		//         
        if (appearance != null) {
            int n = appearance.getIndexCount();
            for (int i = 0; i < n; i++) {
                int attr = appearance.getIndex(i);

                switch (attr) {
                case com.android.internal.R.styleable.TextAppearance_textColorHighlight:
                    textColorHighlight = appearance.getColor(attr, textColorHighlight);
                    break;
              
                case com.android.internal.R.styleable.TextAppearance_textColor:
                    textColor = appearance.getColorStateList(attr);
                    break;
              
                case com.android.internal.R.styleable.TextAppearance_textColorHint:
                    textColorHint = appearance.getColorStateList(attr);
                    break;
                
                case com.android.internal.R.styleable.TextAppearance_textColorLink:
                    textColorLink = appearance.getColorStateList(attr);
                    break;
               
                case com.android.internal.R.styleable.TextAppearance_textSize:
                    textSize = appearance.getDimensionPixelSize(attr, textSize);
                    break;

                case com.android.internal.R.styleable.TextAppearance_typeface:
                    typefaceIndex = appearance.getInt(attr, -1);
                    break;

                case com.android.internal.R.styleable.TextAppearance_textStyle:
                    styleIndex = appearance.getInt(attr, -1);
                    break;

                case com.android.internal.R.styleable.TextAppearance_textAllCaps:
                    allCaps = appearance.getBoolean(attr, false);
                    break;
                }
            }
            appearance.recycle();
       ...
}
}