属性描述符如何使用相同的代码行获取两个控件的值? [英] How can Property Descriptor gets values of two controls using same code line?

问题描述

我在前雇员为自定义 gridview 开发的项目之一中发现了此代码，该自定义控件工作正常，但我不确定它到底在做什么，

I found this code in one of the project developed by an Ex-Employee for custom gridview with custom controls which works fine but I am not sure what exactly it is doing,

代码:

public class aBoundField : ImageField
{
    //here I got some get set properties defined
    protected override void OnDataBindField(object sender, EventArgs e)
    {
        Control control = (Control)sender;

        PropertyDescriptor propertyA = TypeDescriptor.GetProperties(DataBinder.GetDataItem(control.NamingContainer)).Find("boundField", true);
        PropertyDescriptor propertyB = TypeDescriptor.GetProperties(DataBinder.GetDataItem(control.NamingContainer)).Find("boundField", true);

        PropertyAFieldValue = this.GetValue(control.NamingContainer, this._PropertyAField, ref propertyA).ToString();
        PropertyBFieldValue = this.GetValue(control.NamingContainer, this._PropertyBField, ref propertyB).ToString();
            base.OnDataBindField(sender, e);
    }

OnDataBindField 方法中发生了什么，尤其是在获取 PropertyDescriptor 时.我做了一些研究，发现它是一个属性包，但如果它是一个属性包，它如何知道这段代码中属性 A 或属性 B 的值是什么.

What's happening in OnDataBindField method especially when it is getting PropertyDescriptor. I did bit research and figured out that it is a property bag, but if it is a property bag How would it know what value is for property A or Property B in this code.

 PropertyDescriptor propertyA = TypeDescriptor.GetProperties(DataBinder.GetDataItem(control.NamingContainer)).Find("boundField", true);
 PropertyDescriptor propertyB = TypeDescriptor.GetProperties(DataBinder.GetDataItem(control.NamingContainer)).Find("boundField", true);

我不太明白的是

Property Descriptor 如何使用相同的代码行获取两个控件的值

How can Property Descriptor gets values of two controls using same code line

TypeDescriptor.GetProperties(DataBinder.GetDataItem(control.NamingContainer)).Find("boundField", true)

上面的代码行将如何确定它是用于属性 A 还是属性 B.

How would above code line will figure out if its for Property A or Property B.

我试图从一个属性描述符中获取值，认为它是一个属性包，但它没有正常工作.

I tried to get values from one property descriptor thinking its a property bag but it didn't worked properly.

推荐答案

GetValue(control.NamingContainer, this._PropertyAField, ref propertyA)

ProperyA 作为参考，因此在该方法中发生在 propertyA 上的所有事情都将更新上面定义的 propertyA.

ProperyA is given as a reference therefor everything that happens to propertyA inside that method will update propertyA that was defined above.

使用

PropertyDescriptor propertyA = null;

代替

PropertyDescriptor propertyA = TypeDescriptor.GetProperties(DataBinder.GetDataItem(control.NamingContainer)).Find("boundField", true);

仍然有效.

进一步阅读
ref 方法参数关键字

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