C# 可以利用反射给只读属性赋值吗？

结论：可以

验证demo如下：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace IconTest
{
public partial class Form2 : Form
{
public Form2()
{
InitializeComponent();
ReflectTest rt = new ReflectTest();
rt.GetType().GetProperty("ID").SetValue(rt, "Guid", null);
MessageBox.Show(rt.ID);
}

}
public class ReflectTest
{
private string id;
[ReadOnly(true)]
public string ID
{
get
{
return id;
}
set
{
id = value;
}
}
}
}

运行winform程序输出：



小注：

TypeDescriptor.GetProperties用来setvalue这没有作用：

TypeDescriptor.GetProperties(rt)["ID"].SetValue(rt, "Guid");

那么为什么TypeDescriptor.GetProperties用来setvalue没有效果呢？

将上面的代码拆成如下两句：

PropertyDescriptor prop = TypeDescriptor.GetProperties(rt)["ID"];
prop.SetValue(rt, "Guid");

单点跟踪进去，可以发现：



在获取到PropertyDescriptor这个抽象类的实例后，在调用SetValue方法的时候，是从其子类ReflectPropertyDescriptor调用的。





而具体的实现是在子类：ReflectPropertyDescriptor中，从微软源码中找到ReflectPropertyDescriptor及SetValue

public override void SetValue(object component, object value) {
#if DEBUG
if (PropDescUsageSwitch.TraceVerbose) {
string compName = "(null)";
string valName  = "(null)";

if (component != null)
compName = component.ToString();
if (value != null)
valName = value.ToString();

Debug.WriteLine("[" + Name + "]: SetValue(" + compName + ", " + valName + ")");
}
#endif
if (component != null) {
ISite site = GetSite(component);
IComponentChangeService changeService = null;
object oldValue = null;

object invokee = GetInvocationTarget(componentClass, component);

Debug.Assert(!IsReadOnly, "SetValue attempted on read-only property [" + Name + "]");
if (!IsReadOnly) {

// Announce that we are about to change this component
//
if (site != null) {
changeService = (IComponentChangeService)site.GetService(typeof(IComponentChangeService));
Debug.Assert(!CompModSwitches.CommonDesignerServices.Enabled || changeService != null, "IComponentChangeService not found");
}

// Make sure that it is ok to send the onchange events
//
if (changeService != null) {
oldValue = SecurityUtils.MethodInfoInvoke(GetMethodValue, invokee, (object[])null);
try {
changeService.OnComponentChanging(component, this);
}
catch (CheckoutException coEx) {
if (coEx == CheckoutException.Canceled) {
return;
}
throw coEx;
}
}

try {
try {
SecurityUtils.MethodInfoInvoke(SetMethodValue, invokee, new object[] { value });
OnValueChanged(invokee, EventArgs.Empty);
}
catch (Exception t) {
// Give ourselves a chance to unwind properly before rethrowing the exception.
//
value = oldValue;

// If there was a problem setting the controls property then we get:
// ArgumentException (from properties set method)
// ==> Becomes inner exception of TargetInvocationException
// ==> caught here

if (t is TargetInvocationException && t.InnerException != null) {
// Propagate the original exception up
throw t.InnerException;
}
else {
throw t;
}
}
}
finally {
// Now notify the change service that the change was successful.
//
if (changeService != null) {
changeService.OnComponentChanged(component, this, oldValue, value);
}
}
}
}
}

从代码中可以看出来，只读属性直接被跳过去了。。。。。。

那么PropertyInfo有没有什么限制呢？

PropertyInfo调用的SetValue如下所示：



在微软开源的代码中可以找到其具体实现如下：

[DebuggerStepThroughAttribute]
[Diagnostics.DebuggerHidden]
#if !FEATURE_CORECLR
[TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
#endif
public override void SetValue(Object obj, Object value, Object[] index)
{
SetValue(obj,
value,
BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static,
null,
index,
null);
}

[DebuggerStepThroughAttribute]
[Diagnostics.DebuggerHidden]
public override void SetValue(Object obj, Object value, BindingFlags invokeAttr, Binder binder, Object[] index, CultureInfo culture)
{

MethodInfo m = GetSetMethod(true);

if (m == null)
throw new ArgumentException(System.Environment.GetResourceString("Arg_SetMethNotFnd"));

Object[] args = null;

if (index != null)
{
args = new Object[index.Length + 1];

for(int i=0;i<index.Length;i++)
args[i] = index[i];

args[index.Length] = value;
}
else
{
args = new Object[1];
args[0] = value;
}

m.Invoke(obj, invokeAttr, binder, args, culture);
}

暂时没有看到PropertyInfo调用的SetValue有什么限制

PropertyInfo.GetSetMethod 方法 (Boolean)