@ViewDebug.ExportedProperty的使用

• 原文链接：http://daemon369.github.io/android/2014/06/12/android-viewdebug-exportedproperty/
• http://www.eoeandroid.com/thread-55461-1-1.html；

This annotation can be used to mark fields and methods to be dumped by the view server. Only non-void methods with no arguments can be annotated by this annotation. 
这个注释可以用来标记域和方法，该域和方法将会被视服务所“转存”，只有不带参数的非空方法才能被这个注释所诠释；

在查看View源码时，但不清楚@ViewDebug.ExportedProperty的用法：

    /**
     * The view flags hold various views states.
     * {@hide}
     */
    @ViewDebug.ExportedProperty
    int mViewFlags;
 
    /**
     * The distance in pixels from the left edge of this view's parent
     * to the left edge of this view.
     * {@hide}
     */
    @ViewDebug.ExportedProperty(category = "layout")
    protected int mLeft;
    /**
     * The distance in pixels from the left edge of this view's parent
     * to the right edge of this view.
     * {@hide}
     */
    @ViewDebug.ExportedProperty(category = "layout")
    protected int mRight;
    /**
     * The distance in pixels from the top edge of this view's parent
     * to the top edge of this view.
     * {@hide}
     */
    @ViewDebug.ExportedProperty(category = "layout")
    protected int mTop;
    /**
     * The distance in pixels from the top edge of this view's parent
     * to the bottom edge of this view.
     * {@hide}
     */
    @ViewDebug.ExportedProperty(category = "layout")
    protected int mBottom;
 
    /**
     * The offset, in pixels, by which the content of this view is scrolled
     * horizontally.
     * {@hide}
     */
    @ViewDebug.ExportedProperty(category = "scrolling")
    protected int mScrollX;
    /**
     * The offset, in pixels, by which the content of this view is scrolled
     * vertically.
     * {@hide}
     */
    @ViewDebug.ExportedProperty(category = "scrolling")
    protected int mScrollY;
 
    /**
     * The left padding in pixels, that is the distance in pixels between the
     * left edge of this view and the left edge of its content.
     * {@hide}
     */
    @ViewDebug.ExportedProperty(category = "padding")
    protected int mPaddingLeft;
    /**
     * The right padding in pixels, that is the distance in pixels between the
     * right edge of this view and the right edge of its content.
     * {@hide}
     */
    @ViewDebug.ExportedProperty(category = "padding")
    protected int mPaddingRight;
    /**
     * The top padding in pixels, that is the distance in pixels between the
     * top edge of this view and the top edge of its content.
     * {@hide}
     */
    @ViewDebug.ExportedProperty(category = "padding")
    protected int mPaddingTop;
    /**
     * The bottom padding in pixels, that is the distance in pixels between the
     * bottom edge of this view and the bottom edge of its content.
     * {@hide}
     */
    @ViewDebug.ExportedProperty(category = "padding")
    protected int mPaddingBottom;
 
    /**
     * Briefly describes the view and is primarily used for accessibility support.
     */
    private CharSequence mContentDescription;
 
    /**
     * Cache the paddingRight set by the user to append to the scrollbar's size.
     */
    @ViewDebug.ExportedProperty(category = "padding")
    int mUserPaddingRight;
 
    /**
     * Cache the paddingBottom set by the user to append to the scrollbar's size.
     */
    @ViewDebug.ExportedProperty(category = "padding")
    int mUserPaddingBottom;

---

使用@ViewDebug.ExportedProperty注解，我们可以在android提供的工具Monitor(或已经废弃的DDMS)中的Hierarchy Viewer中调试View的属性。我们可以直接观察View的某个变量或方法的值，实时观察View的状态变化。

---

ExprotedProperty注解源码

/**
 * This annotation can be used to mark fields and methods to be dumped by
 * the view server. Only non-void methods with no arguments can be annotated
 * by this annotation.
 */
@Target({ ElementType.FIELD, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
public @interface ExportedProperty {
    /**
     * When resolveId is true, and if the annotated field/method return value
     * is an int, the value is converted to an Android's resource name.
     *
     * @return true if the property's value must be transformed into an Android
     *         resource name, false otherwise
     */
    boolean resolveId() default false;
    /**
     * A mapping can be defined to map int values to specific strings. For
     * instance, View.getVisibility() returns 0, 4 or 8. However, these values
     * actually mean VISIBLE, INVISIBLE and GONE. A mapping can be used to see
     * these human readable values:
     *
     * <pre>
     * @ViewDebug.ExportedProperty(mapping = {
     *     @ViewDebug.IntToString(from = 0, to = "VISIBLE"),
     *     @ViewDebug.IntToString(from = 4, to = "INVISIBLE"),
     *     @ViewDebug.IntToString(from = 8, to = "GONE")
     * })
     * public int getVisibility() { ...
     * <pre>
     *
     * @return An array of int to String mappings
     *
     * @see android.view.ViewDebug.IntToString
     */
    IntToString[] mapping() default { };
    /**
     * A mapping can be defined to map array indices to specific strings.
     * A mapping can be used to see human readable values for the indices
     * of an array:
     *
     * <pre>
     * @ViewDebug.ExportedProperty(indexMapping = {
     *     @ViewDebug.IntToString(from = 0, to = "INVALID"),
     *     @ViewDebug.IntToString(from = 1, to = "FIRST"),
     *     @ViewDebug.IntToString(from = 2, to = "SECOND")
     * })
     * private int[] mElements;
     * <pre>
     *
     * @return An array of int to String mappings
     *
     * @see android.view.ViewDebug.IntToString
     * @see #mapping()
     */
    IntToString[] indexMapping() default { };
    /**
     * A flags mapping can be defined to map flags encoded in an integer to
     * specific strings. A mapping can be used to see human readable values
     * for the flags of an integer:
     *
     * <pre>
     * @ViewDebug.ExportedProperty(flagMapping = {
     *     @ViewDebug.FlagToString(mask = ENABLED_MASK, equals = ENABLED, name = "ENABLED"),
     *     @ViewDebug.FlagToString(mask = ENABLED_MASK, equals = DISABLED, name = "DISABLED"),
     * })
     * private int mFlags;
     * <pre>
     *
     * A specified String is output when the following is true:
     *
     * @return An array of int to String mappings
     */
    FlagToString[] flagMapping() default { };
    /**
     * When deep export is turned on, this property is not dumped. Instead, the
     * properties contained in this property are dumped. Each child property
     * is prefixed with the name of this property.
     *
     * @return true if the properties of this property should be dumped
     *
     * @see #prefix()
     */
    boolean deepExport() default false;
    /**
     * The prefix to use on child properties when deep export is enabled
     *
     * @return a prefix as a String
     *
     * @see #deepExport()
     */
    String prefix() default "";
    /**
     * Specifies the category the property falls into, such as measurement,
     * layout, drawing, etc.
     *
     * @return the category as String
     */
    String category() default "";
}

　　

---

使用

下面是@ViewDebug.ExportedProperty注解的部分属性的使用介绍：

1.category

category用来指定属性的类别，例如measurement, layout, drawing等。我们在自定义View中为使用@ViewDebug.ExportedProperty注解的变量或方法指定category：

@ExportedProperty(category = "marquee")
int x = 1;
@Override
@ExportedProperty(category = "marquee")
public boolean isFocused() {
    return true;
}

运行程序，在Hierarchy Viewer中查看View的属性如下：

2.resolveId

当resolveId为true时，如果使用注解的变量或方法的值为int数据，那么这个值会被转化为对应的Android资源的名称。

在R.java中找到一个资源ID：

public static final int activity_main=0x7f030000;

使用注解属性resolveId：

@ExportedProperty(category = "marquee", resolveId = true)
int b = 0x7f030000;

结果如下：

3.mapping

mapping可以将int值映射到指定的字符串值，例如View.getVisibility()返回的值是int值，View中使用注解将其映射为字符串，其中0为”VISIBLE”，4为”INVISIBLE”，8为”GONE”。我们重载View.getVisibility()并加上我们自己定制的映射：

@Override
@ViewDebug.ExportedProperty(category = "marquee",
        mapping = {
                @ViewDebug.IntToString(from = VISIBLE, to = "MARQUEE_VISIBLE"),
                @ViewDebug.IntToString(from = INVISIBLE, to = "MARQUEE_INVISIBLE"),
                @ViewDebug.IntToString(from = GONE, to = "MARQUEE_GONE")
        })
public int getVisibility() {
    return super.getVisibility();
}

结果如下：

4.indexMapping

indexMapping可以将数组的序号映射为字符串。

@ExportedProperty(category = "marquee",
        indexMapping = {
                @ViewDebug.IntToString(from = 0, to = "MARQUEE_FIRST"),
                @ViewDebug.IntToString(from = 1, to = "MARQUEE_SECOND"),
                @ViewDebug.IntToString(from = 2, to = "MARQUEE_THIRD")
        })
int[] elements = new int[] {
        111, 222, 333
};

结果如下：

---

Demo

package com.daemon.demo;
import android.content.Context;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.view.ViewDebug;
import android.view.ViewDebug.ExportedProperty;
import android.widget.TextView;
public class MarqueeText extends TextView {
    public MarqueeText(Context context) {
        super(context);
    }
    public MarqueeText(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    public MarqueeText(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }
    @Override
    protected void onFocusChanged(boolean focused, int direction, Rect previouslyFocusedRect) {
    }
    @ExportedProperty(category = "marquee")
    int x = 1;
    @Override
    @ExportedProperty(category = "marquee")
    public boolean isFocused() {
        return true;
    }
    @ExportedProperty(category = "marquee", resolveId = true)
    int b = 0x7f030000;
    @Override
    @ViewDebug.ExportedProperty(category = "marquee",
            mapping = {
                    @ViewDebug.IntToString(from = VISIBLE, to = "MARQUEE_VISIBLE"),
                    @ViewDebug.IntToString(from = INVISIBLE, to = "MARQUEE_INVISIBLE"),
                    @ViewDebug.IntToString(from = GONE, to = "MARQUEE_GONE")
            })
    public int getVisibility() {
        return super.getVisibility();
    }
    @ExportedProperty(category = "marquee",
            indexMapping = {
                    @ViewDebug.IntToString(from = 0, to = "MARQUEE_FIRST"),
                    @ViewDebug.IntToString(from = 1, to = "MARQUEE_SECOND"),
                    @ViewDebug.IntToString(from = 2, to = "MARQUEE_THIRD")
            })
    int[] elements = new int[] {
            111, 222, 333
    };
}