上一篇文章我已经介绍了TypeConverterAttribute元数据的作用,本文将通过代码向你展示具体的实现。在这个例子中,我要给控件添加一个复杂的属性,这个属性对这个控件没有什么功用,纯粹是为了演示,有些牵强附会了。
现在在前一篇文章中的创建的控件代码中添加一个Scope属性:
这个属性的类型是Scope类,代码如下:
添加完属性后,build控件工程,然后在测试的工程里选中添加的控件,然后在属性浏览器里观察它的属性,发现Scope属性是灰的,不能编辑。前一篇文章提到了,在属性浏览器里可以编辑的属性都是有类型转换器的,而.NET框架为基本的类型和常用的类型都提供了默认的类型转换器。接下来我们为Scope类添加一个类型转换器,以便这个属性能够被编辑,而且也可以在源代码文件里自动生成相应的代码。下面是类型转换器的代码:
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public class ScopeConverter : TypeConverter
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{
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public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
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{
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if (sourceType == typeof(String)) return true;
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return base.CanConvertFrom(context, sourceType);
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}
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public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType)
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{
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if (destinationType == typeof(String)) return true;
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if (destinationType == typeof(InstanceDescriptor)) return true;
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return base.CanConvertTo(context, destinationType);
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}
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public override object ConvertTo(ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value, Type destinationType)
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{
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String result = "";
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if (destinationType == typeof(String))
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{
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Scope scope = (Scope)value;
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result = scope.Min.ToString()+"," + scope.Max.ToString();
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return result;
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}
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if (destinationType == typeof(InstanceDescriptor))
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{
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ConstructorInfo ci = typeof(Scope).GetConstructor(new Type[]
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{typeof(Int32),typeof(Int32) });
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Scope scope = (Scope)value;
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return new InstanceDescriptor(ci, new object[]
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{ scope.Min,scope.Max });
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}
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return base.ConvertTo(context, culture, value, destinationType);
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}
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public override object ConvertFrom(ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value)
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{
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if (value is string)
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{
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String[] v = ((String)value).Split(',');
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if (v.GetLength(0) != 2)
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{
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throw new ArgumentException("Invalid parameter format");
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}
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Scope csf = new Scope();
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csf.Min = Convert.ToInt32(v[0]);
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csf.Max = Convert.ToInt32(v[1]);
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return csf;
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}
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return base.ConvertFrom(context, culture, value);
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}
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}
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现在我们为类型提供类型转换器,我们在类型前面添加一个TypeConverterAttribute,如下:
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[TypeConverter(typeof(ScopeConverter))]
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public class Scope
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添加完以后build工程,然后切换到测试工程,选中控件,在属性浏览器里查看属性,现在的Scope属性可以编辑了,如下图所示:
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我们修改默认的值,然后看看Form设计器为我们生成了什么代码:
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this.myListControl1.BackColor = System.Drawing.SystemColors.ActiveCaptionText;
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this.myListControl1.Item.Add(1);
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this.myListControl1.Item.Add(2);
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this.myListControl1.Item.Add(3);
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this.myListControl1.Item.Add(6);
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this.myListControl1.Item.Add(8);
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this.myListControl1.Item.Add(9);
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this.myListControl1.Location = new System.Drawing.Point(12, 34);
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this.myListControl1.Name = "myListControl1";
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this.myListControl1.Scope = new CustomControlSample.Scope(10, 200);
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this.myListControl1.Size = new System.Drawing.Size(220, 180);
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this.myListControl1.TabIndex = 1;
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this.myListControl1.Text = "myListControl1";
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关键是这一行this.myListControl1.Scope = new CustomControlSample.Scope(10, 200),Scope类的类型转换器为属性提供了实例化的代码。
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