在集合视图中设置背景颜色时，使用点语法与方括号 [英] Dot syntax vs square brackets when setting background color in collection view

问题描述

我还在学习IOS SDK，所以希望这是有道理的。我仍然试图用点语法来解决问题。有人可以解释为什么这个代码不起作用，但第二个代码呢？

I'm still learning IOS SDK so hopefully this makes sense. I am still trying to wrap my head around using dot syntax. Could some one explain why this code doesn't work but the second one does?

不工作：

-(void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionView *cell = [collectionView cellForItemAtIndexPath:indexPath];
    [[cell contentView] setBackgroundColor:[UIColor blueColor]];
}

工作：

-(void)collectionView:(UICollectionView *)collectionView didDeselectItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionView *cell = [collectionView cellForItemAtIndexPath:indexPath];
    cell.contentView.backgroundColor = [UIColor blueColor];
}

我只是不明白为什么第一个代码不能正常工作。我使用的是最新版本的Xcode。是否将setBackgroundColor方法弃用为其他东西？

I just don't understand why the first code won't work as well. I am using the newest version of Xcode. Was the setBackgroundColor method deprecated into something else?

推荐答案

当您使用点符号时，请记住您 don 't 需要以任何方式更改属性名称。所以如果你说：

When you use dot notation, always keep in mind that you don't need to change the property name in any way. So if you say have:

@property (nonatomic) NSString *message;

编译器负责 setter 和 getter 方法，所以你需要做的就是在这个属性上使用点符号：

The compiler takes care of the setter and getter methods for you, so all you have to do to use the dot notation on this property is this:

self.message;         // getter
self.message = @"hi"; // setter
// the only difference being - which side of the = sign is your property at

另一方面，如果您想要更改setter / getter的行为，那么然后必须定义 setMessage 方法以下方式，实现（不覆盖）您自己的 setter ：

If on the other hand you want to change the behaviour of the setter/getter, you then have to you define the setMessage method in the following way, to implement (not override) your own setter:

- (void)setMessage:(NSString *)message {
    // custom code...
    _message = message;
}

也许这就是你所困惑的。对于 setBackgroundColor ，它仍然存在，你只是不使用点符号访问它，顺便提一下，允许所有种类这样简洁的东西：

Maybe that's what you're confusing. As for setBackgroundColor, it's still there, you just don't access it using the dot notation, which, by the way, allows for all kinds of neat stuff like this:

// .h
@property (nonatomic) int someNumber;

// .m
self.someNumber = 5;   // calls the setter, sets property to 5
self.someNumber += 10; // calls the setter and getter, sets property to 15
self.someNumber++;     // calls the setter and getter, sets property to 16

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