objective-c - iOS 中调用方法有什么区别

Question

假设我调用

[self methodname] 

以及其他

[self performSelector:@selector(methodname) withObject:nil];

Answer 1

没有任何区别。

直接来自documentation performSelector:

The performSelector: method is equivalent to sending an aSelector message directly to the receiver. For example, all three of the following messages do the same thing:

id myClone = [anObject copy];
id myClone = [anObject performSelector:@selector(copy)];
id myClone = [anObject performSelector:sel_getUid("copy")];

尽管具体情况没有区别，但是 performSelector: 存在的原因是它允许调用在编译时可能不可用的任意选择器，如文档中所述:

However, the performSelector: method allows you to send messages that aren’t determined until runtime. A variable selector can be passed as the argument:

SEL myMethod = findTheAppropriateSelectorForTheCurrentSituation();
[anObject performSelector:myMethod];

上述注意事项也适用于两个变体 performSelector:withObject:、performSelector:withObject:withObject:。

另请注意，这不适用于另一组方法，即

• performSelector:withObject:afterDelay:
• performSelector:withObject:afterDelay:inModes:
• performSelectorOnMainThread:withObject:waitUntilDone:
• performSelectorOnMainThread:withObject:waitUntilDone:modes:
• performSelector:onThread:withObject:waitUntilDone:
• performSelector:onThread:withObject:waitUntilDone:modes:
• performSelectorInBackground:withObject:

更多信息请点击:Does performSelector perform right away or is it scheduled to be performed?