c# – Mono.Cecil自动实现的属性访问后备字段

我正在使用Mono.Cecil在自动实现的属性设置器中注入一些IL代码.问题是,我可以从TypeDefinition.Fields对象中引用它,但是当我使用该引用注入ldfld指令(在ldarg.0指令之后)时,它会导致应用程序中断,并且引发CLR无效程序检测到的异常.我还试图反编译ILSpy并在get_Item(int32)方法中获得异常Mono.Cecil参数超出范围的exepction.所以它就像我在编译器创建它之前尝试访问支持字段,但不知何故,Mono.Cecil在加载程序集时可以看到它.

public class ILTesting
{
    public int Counter { get; set; }
} 

这是注入前setter的样子：

IL_0000: ldarg.0
IL_0001: ldarg.1
IL_0002: stfld int32 SyringeWpfTest.ILTesting::'<Counter>k__BackingField'
IL_0007: ret

这是注射码：

var fieldName = "<" + property.Name + ">k__BackingField";
var fieldRef = ilTestType.Fields.Single(field => field.Name == fieldName);
var setterInstruction = property.SetMethod.Body.Instructions;

setterInstructions.Insert(0, Instruction.Create(OpCodes.Brfalse_S, setterInstructions.Last()));
setterInstructions.Insert(0, Instruction.Create(OpCodes.Ldloc_0));
setterInstructions.Insert(0, Instruction.Create(OpCodes.Stloc_0));
setterInstructions.Insert(0, Instruction.Create(OpCodes.Ceq));
setterInstructions.Insert(0, Instruction.Create(OpCodes.Ldc_I4_0));
setterInstructions.Insert(0, Instruction.Create(OpCodes.Ceq));
setterInstructions.Insert(0, Instruction.Create(OpCodes.Ldarg_1));
setterInstructions.Insert(0, Instruction.Create(OpCodes.Ldfld, reference));
setterInstructions.Insert(0, Instruction.Create(OpCodes.Ldarg_0));
setterInstructions.Insert(0, Instruction.Create(OpCodes.Nop));

这是我得到的IL：

IL_0000: nop
IL_0001: ldarg.0
IL_0002: ldfld int32 SyringeWpfTest.ILTesting::'<Counter>k__BackingField'
IL_0007: ldarg.1
IL_0008: ceq
IL_000a: ldc.i4.0
IL_000b: ceq
IL_000d: stloc.0
IL_000e: ldloc.0
IL_000f: brfalse.s IL_001a

IL_0011: nop
IL_0012: ldarg.0
IL_0013: ldarg.1
IL_0014: stfld int32 SyringeWpfTest.ILTesting::'<Counter>k__BackingField'
IL_0019: nop

IL_001a: ret

因此注入代码没有中断,对支持字段的引用存在,但在IL中看起来根本没有支持字段.

解决方法:

问题解决了！这不是财产,而是IL的工作方式.我用代码制作了一个完整的属性：

private int _counter;

public int Counter
{
     get { return _counter; }
     set
     {
          if (_counter != value)
          {
               _counter = value;
               NotifyUI();
          }
      }
}

我在ILSpy中打开了程序集,IL代码就像我注入到自动实现的属性一样.但后来我反编译IL以查看反编译后的C#代码是什么样的,代码看起来像：

private int _counter;

public int Counter
{
     get { return _counter; }
     set
     {
          bool flag = _counter != value; //THIS THING MADE MY LIFE SO HARD FOR A FEW DAYS!
          if (flag)
          {
               _counter = value;
               NotifyUI();
          }
      }
}

所以,问题是在方法堆栈框架上缺少局部变量.在方法中插入局部变量后,一切都很完美.

myProperty.SetMethod.Body.Variables.Add(new VariableDefinition(assembly.MainModul.Import(typeof(bool)));

标签：c,code-injection,mono-cecil
来源： https://codeday.me/bug/20190706/1399179.html