015-CFBridgingRelease简析

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一、CFBridgingRelease

Moves a non-Objective-C pointer to Objective-C and also transfers ownership to ARC.

把非OC的指针指向OC并且转换成ARC。

二、Declaration

id CFBridgingRelease(CFTypeRef X);

三、Discussion

You use this function to cast a Core Foundation-style object as an Objective-C object and transfer ownership of the object to ARC such that you don’t have to release the object, as illustrated in this example:

使用举例如下：

CFStringRef cfName = ABRecordCopyValue(person, kABPersonFirstNameProperty);
NSString *name = (NSString *)CFBridgingRelease(cfName);

四、相关CFBridgingRetain

Casts an Objective-C pointer to a Core Foundation pointer and also transfers ownership to the caller.

使用举例：

NSString *string = <#Get a string#>;
CFStringRef cfString = (CFStringRef)CFBridgingRetain(string);
// Use the CF string.
CFRelease(cfString);

五、实战使用

字符串分类，让字符串转url

/**
 字符串转url

 @return 由字符串转化成的NSURL
 */
- (NSURL *)url;

/**
 字符串转url
 
 @return 由字符串转化成的NSURL
 */
- (NSURL *)url {
    return [NSURL URLWithString:(NSString *)CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault, (CFStringRef)self, (CFStringRef)@"!$&'()*+,-./:;=?@_~%#[]", NULL, kCFStringEncodingUTF8))];
}

六、附CFURLCreateStringByAddingPercentEscapes

Creates a copy of a string, replacing certain characters with the equivalent percent escape sequence based on the specified encoding.

创建一个字符串副本，代替并使用指定格式编码。

6.1 Declaration

定义：

CFStringRef CFURLCreateStringByAddingPercentEscapes(CFAllocatorRef allocator, CFStringRef originalString, CFStringRef charactersToLeaveUnescaped, CFStringRef legalURLCharactersToBeEscaped, CFStringEncoding encoding);

6.2 参数

• allocator

The allocator to use to allocate memory for the new CFString
 object. Pass NULL
 or kCFAllocatorDefault to use the current default allocator.

这个参数传NULL和kCFAllocatorDefault就行

• originalString

The CFString object to copy.

传一个CFString对象

• charactersToLeaveUnescaped

Characters whose percent escape sequences you want to leave intact. Pass NULL to specify that all illegal characters be escaped.

字符转义，传NULL指定所有非法字符转义。
如例所示，里面的字符在url中是非法的，需要转义。

• legalURLCharactersToBeEscaped

Legal characters to be escaped. Pass NULL to specify that no legal characters be replaced.

合法字符除外。传NULL指定不合法字符被替换。

• encoding
  编码格式，毫无疑问的UTF8。

6.3 返回值

A copy of originalString replacing certain characters.

一份原始字符串取代了某些字符。

6.4 例子里使用CFURLCreateStringByAddingPercentEscapes刚好合适

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