Question

访问propertygrid时，只会调用ConvertTo方法（很多次）。这正确地返回了“Foo！” propertygrid中的字符串。当我点击编辑时，我得到一个例外Cannot convert object of type Foo to type System.String.（不完全是翻译的）。 ConvertFrom方法没有被调用，任何线索为什么？并且错误表明它正在尝试转换为字符串，而不是来自。

我想当我想编辑这个对象时，它必须从Foo转换为字符串，并在完成编辑后。

StringConverter类：

public class FooTypeConverter : StringConverter {
    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value) {
        return new Foo((string) value);
    }

    public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType) {
        return "Foo!";
    }

    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType) {
        return true;
    }

    public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType) {
        return true;
    }
}

正在访问的财产：

Foo _foo = new Foo();
[Editor(typeof(System.ComponentModel.Design.MultilineStringEditor), typeof(UITypeEditor))]
[TypeConverter(typeof(FooTypeConverter))]
public Foo Foo {
    get {
        return _foo;
    }
    set {
        _foo = value;
    }
}

Answer 1

重新更新;这是一个FooEditor应该作为一个垫片：

class FooEditor : UITypeEditor
{
    MultilineStringEditor ed = new MultilineStringEditor();
    public override object EditValue(ITypeDescriptorContext context, IServiceProvider provider, object value)
    {
        Foo foo = value as Foo;
        if (foo != null)
        {
            value = new Foo((string)ed.EditValue(provider, foo.Value));
        }
        return value;        
    }
    public override UITypeEditorEditStyle GetEditStyle(ITypeDescriptorContext context)
    {
        return ed.GetEditStyle();
    }
    public override bool  IsDropDownResizable {
        get { return ed.IsDropDownResizable; }
    }
}

你显然需要关联它：

[TypeConverter(typeof(FooTypeConverter))]
[Editor(typeof(FooEditor), typeof(UITypeEditor))]
class Foo { /* ... */ }

Answer 2

无法复制;这对我来说可以;您应该测试destinationType和value的类型，顺便说一句 - 但这并不能阻止它调用ConvertFrom。您是否有一个完整的示例（可能基于以下内容）显示不调用ConvertFrom？

using System;
using System.ComponentModel;
using System.Globalization;
using System.Windows.Forms;
public class FooTypeConverter : StringConverter {
    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
    {
        return new Foo("FooTypeConverter.ConvertFrom: " + Convert.ToString(value));
    }
    public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
    {
        return "FooTypeConverter.ConvertTo: " + ((Foo)value).Value;
    }
    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
    {
        return true;
    }
    public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType)
    {
        return true;
    }
}
[TypeConverter(typeof(FooTypeConverter))]
class Foo
{
    public string Value { get; set; }
    public Foo(string value) { Value = value; }

    public override string ToString()
    {
        return "Foo.ToString";
    }
}
class Test
{
    public Foo Foo { get; set; }

    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        using(Form form = new Form())
        using (PropertyGrid grid = new PropertyGrid())
        {
            grid.Dock = DockStyle.Fill;
            grid.SelectedObject = new Test { Foo = new Foo("Main") };
            form.Controls.Add(grid);
            Application.Run(form);
        }
    }
}

propertygrid中的TypeConverter只能从字符串转换而不是转换为

2 个答案: