如何注册应与值类型一起使用的 DependencyProperty

Question

在 C++/CX 中 class 我想创建一个 DependencyProperty 来获取或设置一个普通的 C++ float 值类型，但我不知道我需要如何指定DependencyProperty::Register.

期望的类型

我举个例子。如果我要使用与引用类型一起使用的属性，我会将以下内容放入我的 C++/CX class:

的头文件中

public:

  static property Windows::UI::Xaml::DependencyProperty^ BackgroundColorProperty
  {
    Windows::UI::Xaml::DependencyProperty^ get();
  };

  property Windows::UI::Xaml::Media::Brush^ BackgroundColor
  {
    Windows::UI::Xaml::Media::Brush^ get();
    void set(Windows::UI::Xaml::Media::Brush^ value);
  };

private:

  static Windows::UI::Xaml::DependencyProperty^ _backgroundColorProperty;

  static void OnBackgroundColorChanged(Windows::UI::Xaml::DependencyObject^ d, Windows::UI::Xaml::DependencyPropertyChangedEventArgs^ e);

实现看起来像这样：

DependencyProperty^ MyCustomClass::BackgroundColorProperty::get()
{
  return _backgroundColorProperty;
}

Windows::UI::Xaml::Media::Brush^ MyCustomClass::BackgroundColor::get()
{
  return static_cast<Windows::UI::Xaml::Media::Brush^>(GetValue(BackgroundColorProperty));
}

void MyCustomClass::BackgroundColor::set(Windows::UI::Xaml::Media::Brush^ value)
{
  SetValue(BackgroundColorProperty, value);
}

DependencyProperty^ MyCustomClass::_backgroundColorProperty =
  DependencyProperty::Register("BackgroundColor",
                               Brush::typeid,
                               MyCustomClass::typeid,
                               ref new PropertyMetadata(ref new SolidColorBrush(Windows::UI::ColorHelper::FromArgb(255, 255, 255, 255)), ref new PropertyChangedCallback(&MyCustomClass::OnBackgroundColorChanged)));

void MyCustomClass::OnBackgroundColorChanged(DependencyObject^ d, DependencyPropertyChangedEventArgs^ e)
{
  MyCustomClass^ myClass = static_cast<MyCustomClass^>(d);
  // Do whatever needs to be done
}

一切正常。 Visual Studio 的 XAML 设计师认识到属性并且一切都按预期工作。

但是假设我想要一个使用 float 而不是 Brush 的属性。我需要如何在 DependencyProperty::Register 方法中指定必要的类型？我指的是下面代码中的第二个参数。

DependencyProperty^ MyCustomClass::_backgroundColorProperty =
  DependencyProperty::Register("BackgroundColor",
                               /* How do I specify the type of the float here?*/,
                               MyCustomClass::typeid,
                               ref new PropertyMetadata(1.0f, ref new PropertyChangedCallback(&MyCustomClass::OnBackgroundColorChanged)));

我尝试了以下方法，但没有用：

ref new TypeKind(TypeKind::Primitive, float32)
typeof(float32)
typeof(float)
typeid(float)
ref new Windows::UI::Xaml::Interop::TypeKind(TypeKind::Primitive, float)
ref new Windows::UI::Xaml::Interop::TypeKind(TypeKind::Primitive, typeid(float))

Answer 1

可以直接使用float::typeid注册float类型

DependencyProperty^ MyCustomClass::_backgroundColorProperty =
DependencyProperty::Register("BackgroundColor",
    float::typeid,
    MyCustomClass::typeid,
    ref new PropertyMetadata(1.0f, ref new PropertyChangedCallback(&MyCustomClass::OnBackgroundColorChanged)));

此外，从这个document，它提到：

If you want a DP with a floating-point type, then make it double (Double in MIDL 3.0). Declaring and implementing a DP of type float (Single in MIDL), and then setting a value for that DP in XAML markup, results in the error Failed to create a 'Windows.Foundation.Single' from the text ''.

所以我建议你使用双依赖属性而不是浮动。

如何注册应与值类型一起使用的 DependencyProperty

How to register a DependencyProperty that shall work with a value type

winrt-xaml

uwp-xaml

c++-cx