停止 enumerateAttribute:inRange:options:usingBlock: 使用 nil 值调用我的块
我在没有 kCTFontAttributeName 范围的现有 NSAttributedString 上调用以下选择器：
[attributedString enumerateAttribute:(NSString *) kCTFontAttributeName
inRange:NSMakeRange(0, [attributedString length])
options:NSAttributedStringEnumerationLongestEffectiveRangeNotRequired
usingBlock:^(id value, NSRange range, BOOL *stop) {
NSLog(@"Attribute: %@, %@", value, NSStringFromRange(range));
}];
我得到下面的输出，但我希望不会得到任何输出。建议？
Attribute: (null), {0, 27}
Attribute: (null), {27, 1}
Attribute: (null), {28, 1}
Attribute: (null), {29, 1}
Attribute: (null), {30, 1}
I'm calling the following selector on an existing NSAttributedString with no kCTFontAttributeName ranges:
[attributedString enumerateAttribute:(NSString *) kCTFontAttributeName
inRange:NSMakeRange(0, [attributedString length])
options:NSAttributedStringEnumerationLongestEffectiveRangeNotRequired
usingBlock:^(id value, NSRange range, BOOL *stop) {
NSLog(@"Attribute: %@, %@", value, NSStringFromRange(range));
}];
and I get the output below, but I would expect to get no output. Suggestions?
Attribute: (null), {0, 27}
Attribute: (null), {27, 1}
Attribute: (null), {28, 1}
Attribute: (null), {29, 1}
Attribute: (null), {30, 1}
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简短的回答？
-enumerateAttribute:inRange:options:usingBlock:并没有按照您（或我最初）的想法进行操作。从名称来看，您可能会假设它仅枚举包含给定属性的接收器范围。事实并非如此。它总是枚举整个字符串。它为它遇到的每个运行调用块。传递到块中的
value设置为该运行的给定属性的值。如果当前运行不包含给定属性，则会传递nil作为value。因此，对于不包含给定属性的字符串，它仍然会触发该块，但
value将始终为nil。对于完全被给定属性（具有相同值）覆盖的字符串，您希望该块触发一次，且value等于该属性在字符串中的值。对于部分被给定属性覆盖的字符串，您会期望该块会触发多次，有时使用value为nil，有时使用value等于属性的值。希望有帮助。我也花了一段时间才从正确的方向看它。
The short answer?
-enumerateAttribute:inRange:options:usingBlock:doesn't do what you (or I, originally) thought it does.From the name, you might assume it only enumerates over ranges of the receiver that contain the given attribute. This is not the case. It always enumerates over the entire string. It calls the block for each run it encounters. The
valuepassed into the block is set to the value the given attribute for that run. If the current run doesn't contain the given attribute, it passesnilforvalue.Thus, for a string that does not contain the given attribute, it will still fire the block, but the
valuewill always benil. For a string that that is completely covered by the the given attribute (with the same value), you would expect the block to fire once withvaluebeing equal to that attribute's value in the string. For a string that is partially covered by the given attribute, you would expect the block to fire multiple times, sometimes with avalueofnil, and sometimes with avalueequal to that of the attribute.Hope that helps. It took me a while to look at it from the correct direction, also.