如何检查依赖项对象是否包含依赖项属性？

Question

基本上我想要一些简单的反射，我有一个任意的DependencyProperty作为参数。如果DependencyProperty由PlaneProjection的/ property定义，我会有一个特殊情况（例如在if语句中）。我已经完成了一些简单的GetType（），但没有像MemberType这样的预期getter运气。

public void SomeFunc(DependencyProperty dp)
{
    // if dp is a dependency property of plane projection, do something
    // would maybe look like PlaneProjection.hasProperty(dp)
}

Answer 1

尝试使用扩展方法的代码：

public static class Helpers
{
    public static DependencyProperty FindDependencyProperty(this DependencyObject target, string propName)
    {
        FieldInfo fInfo = target.GetType().GetField(propName, BindingFlags.Static | BindingFlags.FlattenHierarchy | BindingFlags.Public);

        if (fInfo == null) return null;

        return (DependencyProperty)fInfo.GetValue(null);
    }

    public static bool HasDependencyProperty(this DependencyObject target, string propName)
    {
        return FindDependencyProperty(target, propName) != null;
    }

    public static string GetStaticMemberName<TMemb>(Expression<Func<TMemb>> expression)
    {
        var body = expression.Body as MemberExpression;

        if (body == null) throw new ArgumentException("'expression' should be a member expression");

        return body.Member.Name;
    }
}

用法：

planeProjection1.HasDependecyProperty(
    Helpers.GetStaticMemberName(() => PlaneProjection.CenterOfRotationXProperty));

Answer 2

这种情况会发现吗？

编辑：仅在WPF中 - 而不是SilverLight。

dp.OwnerType.IsAssignableFrom(typeof(PlaneProjection))

Answer 3

这应该照顾您在SilverLight中的需求：

private static readonly Dictionary<DependencyProperty, Type> _ownerCache = new Dictionary<DependencyProperty, Type>();
// normally you'd use a HashSet<DependencyProperty>, but it's not available in SilverLight
private static readonly Dictionary<Type, Dictionary<DependencyProperty, bool>> _excludeCache = new Dictionary<Type, Dictionary<DependencyProperty, bool>>();

public static bool IsOwnedByTypeOrParent(DependencyProperty dp, Type type)
{
    lock (_ownerCache)
    {
        Type owner;
        if (_ownerCache.TryGetValue(dp, out owner))
            return owner.IsAssignableFrom(type);

        Dictionary<DependencyProperty, bool> exclude;
        if (_excludeCache.TryGetValue(type, out exclude))
        {
            if (exclude.ContainsKey(dp))
                return false;
        }

        FieldInfo[] fields = type.GetFields(BindingFlags.Static | BindingFlags.FlattenHierarchy);
        foreach (FieldInfo field in fields)
        {
            if (typeof(DependencyProperty).IsAssignableFrom(field.FieldType))
            {
                try
                {
                    object value = field.GetValue(null);
                    if (object.ReferenceEquals(dp, value))
                    {
                        _ownerCache[dp] = field.DeclaringType;
                        return true;
                    }
                }
                catch
                {
                }
            }
        }

        if (exclude == null)
        {
            exclude = new Dictionary<DependencyProperty, bool>();
            _excludeCache[type] = exclude;
        }

        exclude.Add(dp, false);

        /* optional if you want to minimize memory overhead. unnecessary unless
         * you are using this on enormous numbers of types/DPs
         */
        foreach (var item in _excludeCache)
        {
            item.Value.Remove(dp);
        }

        return false;
    }
}

Answer 4

依赖项属性具有默认值，并且在检索时始终显示为设置为某些内容。

您可以检查是否已在依赖项对象上设置依赖项属性，如果是，通过使用帮助程序DependencyPropertyHelper类检索和检查其ValueSource，请考虑以下内容：

public static IsPropertyDefault(this DependencyObject obj, DependencyProperty dp)
{
  return DependencyPropertyHelper.GetValueSource(obj, dp).BaseValueSource 
    == BaseValueSource.Default;
}

public static IsPropertySetLocally(this DependencyObject obj, DependencyProperty dp)
{
  return DependencyPropertyHelper.GetValueSource(obj, dp).BaseValueSource 
    == BaseValueSource.Local;
}

其中一个应该对你有用;如果你的依赖属性可以通过继承设置并且你关心它，你可以检查！IsPropertyDefault。如果您特别关心是否已在对象上直接显式声明属性，则可以检查IsPropertySetLocally。