【Objc-C】Toll-Free Bridging : 無損橋接

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Toll-Free Bridging : 無損橋接

在 ARC 管理中，常會看到這個名詞

簡單來說就是因為 OC 是 C 的執行庫，而為了讓 OC 可以與 C 進行資料交換，就得利用 Toll-Free Bridging 進行資料格式的交換 如 NSArray 與 CFArray 參考

CFArray is “toll-free bridged” with its Cocoa Foundation counterpart, NSArray. This means that the Core Foundation type is interchangeable in function or method calls with the bridged Foundation object. Therefore, in a method where you see an NSArray * parameter, you can pass in a CFArrayRef, and in a function where you see a CFArrayRef parameter, you can pass in an NSArray instance. This also applies to concrete subclasses of NSArray. See Toll-Free Bridged Types for more information on toll-free bridging.

Toll-Free Bridged Types

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NSArray *_array = [[NSArray alloc]init]; 
NSString *values = {@"foo",@"bar"}; 
CFArrayRef arrayRef = CFArrayCreate(kCFAllocatorDefault, (void *)values, (CFIndex)2,NULL); 
NSArray *array = (__bridgeNSArray *)arrayRef;//注意這一行的__bridge 
NSDa

NSString -> CFString

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NSString *foo = @"bar"; 
CFStringRef bar = (__bridge CFStringRef)(foo); 
NSLog(@"%ld", CFStringGetLength(bar));

CFString -> NSString

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CFStringRef foo = CFStringCreateWithCString(kCFAllocatorDefault, "foo", kCFStringEncodingUTF8); 
NSString *bar = (__bridge NSString *)(foo);
NSLog(@"%ld", bar.length); 
CFRelease(foo);

__bridge

目的在於處理 ARC <-> MRC 間的溝通

而 『MRC 下的 Toll－Free Bridging 因為不涉及記憶體管理的轉移，相互之間可以直接交換使用。』

Toll-Free Bridged Types 中，有支援 Toll-Free Bridging 的對照表