問題描述

這對我來說似乎很奇怪——VB.NET 通過它的 RaiseEvent 關(guān)鍵字隱式地處理空檢查.它似乎大大增加了圍繞事件的樣板數(shù)量，我看不出它提供了什么好處.

This seems odd to me -- VB.NET handles the null check implicitly via its RaiseEvent keyword. It seems to raise the amount of boilerplate around events considerably and I don't see what benefit it provides.

我確信語言設(shè)計者有充分的理由這樣做..但我很好奇是否有人知道原因.

I'm sure the language designers had a good reason to do this.. but I'm curious if anyone knows why.

推薦答案

這當(dāng)然是一個煩惱點.

當(dāng)您編寫訪問類中類似字段的事件的代碼時，您實際上是在訪問該字段本身(以 C# 4 中的一些更改為模；我們暫時不去那里).

When you write code which accesses a field-like event within a class, you're actually accessing the field itself (modulo a few changes in C# 4; let's not go there for the moment).

所以，選項是:

• 特殊情況下的類似字段的事件調(diào)用，以便它們實際上并不直接引用該字段，而是添加了一個包裝器

• 以不同的方式處理所有委托調(diào)用，例如:

Action<string> x = null;
x();

不會拋出異常.

當(dāng)然，對于非無效委托(和事件)，這兩種選擇都會產(chǎn)生問題:

Of course, for non-void delegates (and events) both options raise a problem:

Func<int> x = null;
int y = x();

應(yīng)該默默地返回0嗎?(int 的默認(rèn)值.)或者它實際上掩蓋了一個錯誤(更有可能).讓它默默地忽略您試圖調(diào)用空委托的事實會有些不一致.在這種情況下會更奇怪，它不使用 C# 的語法糖:

Should that silently return 0? (The default value of an int.) Or is it actually masking a bug (more likely). It would be somewhat inconsistent to make it silently ignore the fact that you're trying to invoke a null delegate. It would be even odder in this case, which doesn't use C#'s syntactic sugar:

Func<int> x = null;
int y = x.Invoke();

基本上，無論您做什么，事情都會變得棘手且與語言的其余部分不一致.我也不喜歡它，但我不確定一個實用但一致的解決方案可能是什么......

Basically things become tricky and inconsistent with the rest of the language almost whatever you do. I don't like it either, but I'm not sure what a practical but consistent solution might be...

這篇關(guān)于為什么 C# 要求您每次觸發(fā)事件時都編寫空檢查?的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網(wǎng)！