对于Objective-C，我绝对是初学者！任何帮助都将非常感激。
这段代码对我有用，但我觉得将来肯定会对我有所影响。例如，如果有人在for循环中调用autorelease drain，该怎么办？另外，itemPtr和stackbuf之间的区别是什么？ Apple网站上的NSFastEnumeration文档非常薄弱，我的代码行为与描述不符：
stackbuf
A C array of objects over which the sender is to iterate.
itemsPtr
A C array of objects
这不是很有帮助。我只使用itemsPtr，它的工作原理。究竟我应该怎么处理stackbuf以及如何处理stackbuf和itemsPtr的内存分配/释放？我在macosx-dev（2009年10月）上阅读了这个讨论，实现了NSFastEnumeration，并且对我不知道发生了什么感到更加自信。
所以......帮忙！这是正确的吗？我该如何做得更好？我应该怎么做stackBuf？如何休息时遇到麻烦？
代码作为源文件：http://vislab-ccom.unh.edu/~schwehr/Classes/2010/mbnutsandbolts/simple-fast-enum2.m（我在C ++中共同教授本课程，但试图在ObjC中为自己做一切）
001: #import <Foundation/Foundation.h>
002: #include <assert.h>
003:
004: @interface Datagram : NSObject
005: {
006: int dgId;
007: }
008: -(id)initWithDatagramType:(int)datagramType;
009: -(void)dealloc;
010: -(NSString *)description;
011: @property (readonly) int dgId;
012: @end
013:
014: @implementation Datagram
015: @synthesize dgId;
016: - (NSString *)description {
017: return [NSString stringWithFormat: @"Datagram: dgId:", dgId];
018: }
019:
020: -(id)initWithDatagramType:(int)datagramType {
021: self = [super init];
022: if (!self) return self;
023: dgId = datagramType;
024: return self;
025: }
026:
027: -(void)dealloc {
028: NSLog(@"dealloc datagram: %d",dgId);
029: [super dealloc];
030: }
031: @end
032:
033: // Pretend sequence of packet ID's coming from a sonar
034: int testSeq[] = {
035: 3, 12, 4, 19, 8,
036: 2, 2, 2, 2, 2, 2, 2, 2, 2, 9,
037: 2, 2, 2, 2, 9,
038: 2,2,2,2,9,
039: 1,2,3,4,5,6,7,8,9,
040: 11,12,13,14,15,16,17,18,19,
041: 3,
042: 0 // End of sequence / array sentinal
043: };
044:
045: @interface DatagramFile : NSObject <NSFastEnumeration>
046: {
047: // No ivars
048: }
049: -(id)init;
050: @end
051:
052: @implementation DatagramFile
053: -(id)init {
054: self = [super init];
055: if (!self) return self;
056: // NOP
057: return self;
058: }
059:
060: - (NSUInteger)countByEnumeratingWithState:(NSFastEnumerationState *)state objects:(id *)stackbuf count:(NSUInteger)len
061: {
062: NSLog(@"In countByEnumeratingWithState: stackbuf: %p, count: %d", stackbuf, len);
063: NSLog(@"\t state struct: state=%d %p %p", state->state, state->itemsPtr, state->mutationsPtr);
064: if (stackbuf) {
065: NSLog(@"***INSPECTING STACKBUF\n");
066: for(int i=0;i<1000 && stackbuf[i]!=0;i++) {
067: NSLog(@"Stackbuf %d: %p",i,stackbuf[i]); // What should I do with stackbuf[i]?
068: }
069: }
070: if (0 == state->state) {
071: NSLog(@"Initializing loop");
072: assert(0==state->itemsPtr);
073: state->itemsPtr = malloc(sizeof(id)*16);
074: memset(state->itemsPtr, 0, sizeof(id)*16);
075: } else if (0==len) {
076: // Will this get called if the call uses break inside the for loop?
077: NSLog(@"Finished loop. cleanup");
078: free(state->itemsPtr);
079: state->itemsPtr = 0;
080: return 0;
081: }
082: state->mutationsPtr = (unsigned long *)self; // Tell the caller that the file has not changed
083:
084: NSUInteger count=0;
085: for (; count < len && testSeq[state->state]!=0; count++, state->state++) {
086: NSLog(@"Creating datagram of type %d state: %d count %d",testSeq[state->state], state->state, count);
087: Datagram *dg = [[Datagram alloc] initWithDatagramType:testSeq[state->state]];
088: state->itemsPtr[count] = dg;
089: [dg autorelease];
090: }
091: NSLog(@"countByEnumeratingWithState read %d datagrams. state->state: %d",count, state->state);
092: return count;
093: }
094: @end // implementation DatagramFile
095:
096: int main (int argc, const char * argv[]) {
097: NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
098:
099: DatagramFile *df = [[DatagramFile alloc] init];
100: for (Datagram *dg in df) {
101: NSLog(@"About to read datagram in for");
102: NSLog(@" Datagram type: %d", [dg dgId]);
103: }
104:
105: NSLog(@"about to drain pool");
106: [pool drain];
107: NSLog(@"pool drained. ready for winter");
108: return 0;
109: }
答案 0 :(得分：1)
奇;我确信在The Objective-C Programming Language中曾经有过更全面的文档。无论如何，要回答您的具体问题：state->itemsPtr是您放置实际结果的地方。 stackbuf和len提供了可用于此目的的临时空间，但您无需这样做。例如，如果您的集合使用直接C对象引用数组，则可以直接将其放在state->itemsPtr中，从而一次性返回所有对象。
至于你的实施：
stackbuf的初始内容永远不会有用。malloc()而不是stackbuf缓冲区。使用len代替硬编码16。