c# - 我什么时候应该处理异常以及什么时候应该抛出异常？

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在编程时，我发现自己很难思考当可能抛出异常时我的程序应该如何工作。

看下面的例子:

    public void AddComponent(IEntityComponent component)
    {
        if (component == null)
        {
            // Should I throw an ArgumentNullException or should I just return?
        }

        if (ContainsComponentOfType(component.GetType()))
        {
            // Should I return here? Or should I throw an ArgumentException?
        }

        // Finally, we know we can add the component to the entity
        components.Add(component);
    }

    public bool ContainsComponentOfType(Type componentType)
    {
        if (componentType == null)
        {
            // Should I throw an exception here? Should I return false?
        }

        return components.Any(c => c.GetType() == componentType);
    }

请注意，使用我的引擎创建游戏的人将使用上述代码。

Answer 1

该策略可以变化，从零容忍(在任何可以抛出异常的地方抛出异常)到宽松(我们尽可能原谅调用者)。常见的做法是 DoAction (在您的情况下是 AddComponent)严格，而 TryDoAction (TryAddComponent)宽松。

零容忍版本:

// Strict: we are quite sure in the arguments; 
// that's why it's an exceptional case (error in the code!) if arguments are invalid
// and we fail to add 
public void AddComponent(IEntityComponent component) {
  // Contract: here we validate the input arguments
  // Since we sure in them we apply zero tolerance policy:
  // if contract is't met throw corresponding exception

  // we want not null component  
  if (component == null)
    throw new ArgumentException(nameof(component));

  // which contains at least one item of the required type
  if (ContainsComponentOfType(component.GetType()))
    throw new ArgumentException("Component must contain...",  nameof(component)); 

  // Finally, we know we can add the component to the entity
  components.Add(component);
}

宽松的实现

// Lenient: we have arguments from the (unknown) source in which we are not sure
// we want just to try adding (and get true / false) if we succeed or not
public bool TryAddComponent(IEntityComponent component) {
  // Contract: we validate the input arguments from unknown source
  // if validation fails we should not throw any exception (it's not an
  // exceptional case to get incorrect data from unreliable source) but
  // let the caller know that we don't succeed

  // We can't add if component is null
  if (component == null)
    return false;

  // We have nothing to add if component doesn't contain required items 
  if (ContainsComponentOfType(component.GetType()))
    return false;

  // Finally, we know we can add the component to the entity
  components.Add(component);

  return true;
}

// Do we really want to expose it?
// ContainsComponentOfType is an implementation detail which we keep private
private bool ContainsComponentOfType(Type componentType) {
  // Since it's a private method we can omit the check
  return components.Any(c => c.GetType() == componentType);
}

用法:由于您正在构建引擎，两种情况(严格和宽松)都可能出现

MyClass loader = new MyClass();

...

// Cloud Database must not be corrupted; if it is, we want to know it immediatly
loader.AddComponent(componentFromCloud);

...

// Local file can contain any data: it can be corrupted, user can try cheating etc.
if (!loader.TryAddComponent(componentFromLocalFile)) {
  // Let user know that saved data failed to be loaded 
}