当前位置：网站首页>C＃可以利用反射给只读属性赋值吗？

C＃可以利用反射给只读属性赋值吗？

2022-07-26 06:34:00 【51CTO】

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;
       
            }
       
        }
       
    }
       
}
      
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.

运行winform程序输出：

C# 可以利用反射给只读属性赋值吗？_反射

小注：

TypeDescriptor.GetProperties用来setvalue这没有作用：

       
       TypeDescriptor.
       
       GetProperties(
       
       rt)[
       
       "ID"].
       
       SetValue(
       
       rt, 
       
       "Guid");
      
1.

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");
      
1.
2.

单点跟踪进去，可以发现：

C# 可以利用反射给只读属性赋值吗？_属性_02

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。

C# 可以利用反射给只读属性赋值吗？_只读_03

C# 可以利用反射给只读属性赋值吗？_反射_04

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);
       
                        }
       
                    }
       
                }
       
            }
       
        }
      
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
68.
69.
70.
71.
72.
73.
74.
75.
76.
77.
78.
79.
80.
81.

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：

C# 可以利用反射给只读属性赋值吗？_属性_05

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);
       
        }
      
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.