Question

这是我的简单测试代码。我想在2个对象之间创建字段赋值链接，并且该字段在运行时使用反射通过缓存其setter / getter方法的委托来确定。但是，不知怎的，它不起作用。任务不起作用;也许我犯了一个愚蠢的错误。我哪里错了？

public static class AssignmentExpression
{
    public static Expression Create(Expression left, Expression right)
    {
        MethodInfo m = typeof(AssignmentExpression)
                  .GetMethod("AssignTo", BindingFlags.NonPublic | BindingFlags.Static)
                  .MakeGenericMethod(left.Type);

        return Expression.Call( null,m,left, right);
    }

    private static void AssignTo<T>(ref T left, T right)  
    {                                                     
        left = right;                                     
    }
}

public class FieldLink
{
    protected Delegate srcGetter;
    protected Delegate dstSetter;

    public FieldLink(FieldInfo srcObject, FieldInfo dstObject)
    {
        this.srcGetter = FieldLink.createGetter(srcObject);
        this.dstSetter = FieldLink.createSetter(dstObject);
    }

    public void update<T>(T dst, T src)
    {
        this.dstSetter.DynamicInvoke(dst, this.srcGetter.DynamicInvoke(src));
    }

    protected static Delegate createGetter(FieldInfo field)
    {
        ParameterExpression objParm = Expression.Parameter(field.DeclaringType, "obj");
        Type delegateType = typeof(Func<,>).MakeGenericType(field.DeclaringType, field.FieldType);
        MemberExpression fieldExpr = Expression.Field(objParm, field.Name);
        LambdaExpression lambda = Expression.Lambda(delegateType, fieldExpr, objParm);
        return lambda.Compile();
    }

    protected static Delegate createSetter(FieldInfo field)
    {
        ParameterExpression objParm = Expression.Parameter(field.DeclaringType, "obj");
        ParameterExpression valueParm = Expression.Parameter(field.FieldType, "value");
        Type delegateType = typeof(Action<,>).MakeGenericType(field.DeclaringType, field.FieldType);
        MemberExpression memberExpr = Expression.Field(objParm, field.Name);
        Expression assignExpr = AssignmentExpression.Create(memberExpr, valueParm);
        LambdaExpression lambda = Expression.Lambda(delegateType, assignExpr, objParm, valueParm);
        return lambda.Compile();
    }
}

public class Test
{
    public int fieldInt = 0;
}

public class TestClass
{
    public Test a = new Test();
    public Test b = new Test();
    public void Start()
    {
        a.fieldInt = 5;

        Debug.Log("before a = " + a.fieldInt + " b = " + b.fieldInt);
        FieldLink testLink = new FieldLink(this.a.GetType().GetField("fieldInt"),
                                           this.b.GetType().GetField("fieldInt"));
        testLink.update(this.b, this.a);
        Debug.Log("after  a = " + a.fieldInt + " b = " + b.fieldInt);
        //here a.fieldInt should be equal to b.fieldInt, but somehow its unchanged!
    }
}

Answer 1

您的代码似乎有效，但可能并不完全符合您的预期。当您致电update时，您将b.fieldInt作为left参数传递，将a.fieldInt作为right参数传递; update方法然后将a.fieldInt（5）的值分配给b.fieldInt字段，从而导致两个对象的fieldInt值为5.如果您反转参数，两个字段最终都为零。这不是你所期望的吗？

顺便说一下 - 也许你有其他理由使用你自己的AssignmentExpression课程 - 但你实际上可以替换：

Expression assignExpr = AssignmentExpression.Create(memberExpr, valueParm);

...与：

Expression assignExpr = Expression.Assign(memberExpr, valueParm);

......你得到的结果相同。

Field Setter / Getter使用Delegate

1 个答案: