字典<>在不是

Question

时报告无效密钥我有一些代码在索引0处将一个Func<short>添加到Dictionary<byte, Func<short>>。稍后，包含该字典的类中的某些代码尝试提取此Func（通过TryGetValue）和执行它，如果不起作用则抛出异常。即使被访问的索引是有效的，它也会抛出表示函数提取失败的异常。为什么是这样？在开关的情况下沙漠在你的代码（可以根据需要提供代码）

//processor construction and setup 
    VirtualProcessor processor = new VirtualProcessor(); 
    ... 
    processor.InputChannels.Add(0,() => { return 2; });//the func i'm trying to access 
    //end processor construction and setup 
    //build program 
    Dictionary<short, Command> commands = new Dictionary<short, Command>(); 
    commands.Add(0, CommandFactory.CreateInputCommand(0, 0));//this, in a roundabout way, attempts to call the func 
    commands.Add(1, CommandFactory.CreateLoadCommand(1, 200)); 
    commands.Add(2, CommandFactory.CreateAddCommand(0, 1, 2)); 
    commands.Add(3, CommandFactory.CreateHaltCommand()); 
    //end build program 
    //execution 
    processor.CurrentProgram = commands; 
    processor.ExecuteTillHalt(); 
    //end execution 
    Console.ReadLine(); 

某处，在另一个类...

Func<short> inChannel; 
    InputChannels.TryGetValue(command.Data2, out inChannel);//the attempt to access the func, this is the second value supplied to CreateInputCommand above 
    if (inChannel != null) 
      Registers[command.Data1] = inChannel();//should be here 
    else 
      throw new InvalidInputChannelException("Invalid input channel " + command.Data2); //throws this 

Answer 1

可能是一个错误 - 为什么要使用TryGetValue，然后检查null值？我会将其改写为：

if (InputChannels.TryGetValue(command.Data2, out inChannel)) 
    Registers[command.Data1] = inChannel(); 
else 
    throw ... 

如果其中一个函数返回null，您将得到您描述的结果。

Answer 2

请确保您致电CommandFactory.CreateInputCommand永不返回null。特别是，你的代码表明，它下面的调用返回null：

CommandFactory.CreateInputCommand(0, 0)