更改属性上的ReadOnly标志 [英] Change ReadOnly flag on property

问题描述

我试图通过反射更改只读属性.一切正常的属性运行良好.但是当我使用自定义编辑器时，它不会更改标志.

这是我要更改的属性:

I''ve tried to change a readonly attribute over reflection. Everything runs nice with the normal properties. But when I''m using a custom editor, it doesn''t change the flag.

Here are the properties I want to change:

[UIPathEditor.OfdParams("Video Files|*.wmv", "Choose Background Video")]
 [Editor(typeof(UIPathEditor), typeof(UITypeEditor))]
 [ReadOnly(false)]
 [Description("The background video")]
 [Category("Appearance")]
 public string Video
 {
     get { return _backgroundVideo; }
     set { _backgroundVideo = value; }
 }

 [ReadOnly(false)]
 [Description("The volume of the video")]
 [Category("Appearance")]
 public int Volume
 {
     get { return _volume; }
     set { if (value <= 100 && value >= 0)_volume = value;}
 }

这是我用来执行此操作的代码:

This is the code I use to do this:

PropertyDescriptor property;
           ReadOnlyAttribute attribute;
           FieldInfo isReadOnly;

           property = TypeDescriptor.GetProperties(typeof(MenuProp))["Video"];
           attribute = (ReadOnlyAttribute)property.Attributes[typeof(ReadOnlyAttribute)];
           isReadOnly = attribute.GetType().GetField("isReadOnly", BindingFlags.NonPublic | BindingFlags.Instance);

           isReadOnly.SetValue(attribute, Video);

           property = TypeDescriptor.GetProperties(typeof(MenuProp))["Volume"];
           attribute = (ReadOnlyAttribute)property.Attributes[typeof(ReadOnlyAttribute)];
           isReadOnly = attribute.GetType().GetField("isReadOnly", BindingFlags.NonPublic | BindingFlags.Instance);

           isReadOnly.SetValue(attribute, Volume);

有了音量属性，它运行良好.但是在Video属性上没有任何作用...

我想更改 Attribute [ReadOnly(false)] ，因为它是针对要编辑这些属性的属性网格.而且我想根据所选对象在可编辑和不可编辑之间切换.

With the volume-property it runs fine. But on the Video property it has no effect...

I want to change the Attribute[ReadOnly(false)] because its for a property-grid where I want to edit those properties. And I want to switch between editable and non-editable depending on the choosen object.

推荐答案

至少有一个原因导致它原则上不起作用.您的isReadOnly是一个字段，但是您在谈论的是属性.如果此字段是属性后面的字段，则对其进行修改通常无效.

考虑如何实现(通常以这种方式实现):字段isReadOnly仅用于记住属性的当前值.典型的代码如下所示:

There is at least one reason why it might not work in principle. Your isReadOnly is a field, but you''re talking about a property. If this field is a field behind the property, modification of it usually has no effect.

Think about how it can be implemented (and usually implemented this way): the field isReadOnly is used only to remember current value of the property. The typical code looks like this:

public IsReadOnly {
    get { return isReadOnly; }
    set {
        if (value == isReadOnly) return;
        isReadOnly = value;
        SetReadOnlyCore(value); //all real work is done here
    }
}
bool isReadOnly;

所有实际工作都在设置员的最后完成.为了说明起见，我将其命名为对某些方法SetReadOnlyCore的调用.它可能正在通过P/Invoke调用某些本机方法.

通过Reflection修改字段，您无需调用属性设置器.所以什么都没发生尝试修改属性本身，而不是字段.

—SA

All real work is done at the end of the setter; for illustration, I named is the call to some method SetReadOnlyCore. It could be calling some native method via P/Invoke.

By modifying the field via Reflection you don''t call the property setter; so nothing happens. Try to modify the property itself, not a field.

—SA

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