按钮设置通过BOOL选择 [英] Button Set Selected via BOOL

问题描述

可有人请教育我，为什么下面不工作？这个按钮永远不会被设置为选中状态。

  [self.boldButton的setSelected：isBold];
 

如果我替换上面用if else语句它工作正常。我也可以改变的setSelected值1或0，而不是YES或NO，它仍然能正常工作。

 如果（isBold）
{
    [self.boldButton的setSelected：YES];
}
其他
{
    [self.boldButton的setSelected：NO];
}
 

所以我有一个工作项目，但我不明白为什么这两个实现不实现相同的结果。谢谢你。

FWIW - 我测试用大胆的另一种方法。但如果测试是有缺陷的，我怎么看不到第二个方法可以工作，而第一个还是没有。

   - （BOOL）isBold
{
    CTFontRef fontRef =（CTFontRef）CFBridgingRetain（个体经营）;
    CTFontSymbolicTraits symbolicTraits = CTFontGetSymbolicTraits（fontRef）;
    返回（symbolicTraits＆安培; kCTFontTraitBold）;
}
 

解决方案

BOOL 在＆LT的定义是这样的; objc / objc.h＆GT; ：

 的typedef签署的char BOOL;
 

这意味着 BOOL 通过127在-128实际上可以持有任何值（含）。

- [UIControl的setSelected：] 作品大致是这样的：

 的#define kSelectedBitPosition 10
的#define kSelectedBit（1 <<;＆下; kSelectedBitPosition） - （无效）的setSelected：选择（BOOL）{
    如果（（（自＆GT; _controlFlags＆GT;＆GT; kSelectedBitPosition）及1）==选择）{
        返回;
    }其他{
        自＆GT; _controlFlags =（自＆GT; _controlFlags＆安培;〜kSelectedBit）
            | （（选择＆放大器; 1） - ;＆下; kSelectedBitPosition）;
        [自我setNeedsDisplay];
    }
}
 

（我拆开的UIKit 与霍珀模拟器版本的数字，出。）

所以，注意两件事情：

• 的如果语句的条件只能是真，如果选择== 0 或选择== 1 。如果选为其他值它永远不会为真。




• 赋值语句（即更新 _controlFlags ）只使用选。因此，举例来说，如果选择== -2 ，这是逻辑真在C和有每一位设置的除了的位0，赋值语句仍然不会在 _controlFlags 对位开启。




这意味着您必须通过0或1 以 - [UIControl的setSelected：] 。没有其他的值将可靠地工作。

所有非零值转换为1 C语言中的最短途径是通过应用 操作符两次：！

  [self.boldButton的setSelected：!! isBold];
 

但是，它很可能是更好的解决您的 -isBold 方法返回一个安全的 BOOL 代替

   - （BOOL）isBold {
    CTFontRef fontRef =（CTFontRef）CFBridgingRetain（个体经营）;
    CTFontSymbolicTraits symbolicTraits = CTFontGetSymbolicTraits（fontRef）;
    返回!!（symbolicTraits＆安培; kCTFontTraitBold）;
}
 

Can someone please educate me why the following does not work? The button never gets set to selected.

[self.boldButton setSelected:isBold];

If I replace the above with an if else statement it works fine. I can also change the setSelected values to 1 or 0, instead of YES or NO and it still works fine.

if (isBold)
{
    [self.boldButton setSelected:YES];
}
else
{
    [self.boldButton setSelected:NO];
}

So I have a working project, but I don't understand why these two implementations don't deliver the same results. Thanks.

FWIW - I test for bold with another method. Though if the test were flawed, I don't see how the second approach could work, while the first still doesn't.

- (BOOL)isBold
{
    CTFontRef fontRef = (CTFontRef)CFBridgingRetain(self);
    CTFontSymbolicTraits symbolicTraits = CTFontGetSymbolicTraits(fontRef);
    return (symbolicTraits & kCTFontTraitBold);
}

解决方案

BOOL is defined like this in <objc/objc.h>:

typedef signed char     BOOL;

That means a BOOL can actually hold any value in the range -128 through 127 (inclusive).

-[UIControl setSelected:] works roughly like this:

#define kSelectedBitPosition 10
#define kSelectedBit (1 << kSelectedBitPosition)

- (void)setSelected:(BOOL)selected {
    if (((self->_controlFlags >> kSelectedBitPosition) & 1) == selected) {
        return;
    } else {
        self->_controlFlags = (self->_controlFlags & ~kSelectedBit)
            | ((selected & 1) << kSelectedBitPosition);
        [self setNeedsDisplay];
    }
}

(I disassembled the simulator version of UIKit with Hopper to figure that out.)

So, notice two things:

• The if statement condition can only be true if selected == 0 or selected == 1. It will never be true if selected has any other value.

• The assignment statement (that updates _controlFlags) only uses bit 0 (the 1's bit) of selected. So, for example, if selected == -2, which is logically true in C and has every bit set except bit 0, the assignment statement will still not turn on the bit in _controlFlags.

This means that you must pass 0 or 1 to -[UIControl setSelected:]. No other value will work reliably.

The shortest way to convert all non-zero values to 1 in C is by applying the ! operator twice:

[self.boldButton setSelected:!!isBold];

However, it would probably be better to fix your -isBold method to return a "safe" BOOL instead:

- (BOOL)isBold {
    CTFontRef fontRef = (CTFontRef)CFBridgingRetain(self);
    CTFontSymbolicTraits symbolicTraits = CTFontGetSymbolicTraits(fontRef);
    return !!(symbolicTraits & kCTFontTraitBold);
}

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