IOS_OC_基礎文法

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1.YES與NO

Object-c 提供了 BOOL 類型, 但這個BOOL 類型和 C++裡的並不一樣: 在C++裡一切非 0 值的東西都 為 true,而為 0 值的為 false。但是 Object-c 裡 1 為 true 並被宏定義為 YES=1,0 為 false 並被宏定義為 NO=0。

+ (BOOL)isEquals:(int)x with:(int)y{    return x - y;}if ([Provider isEquals:10 with:1021]) {// == YES //error        NSLog(@" !!!!!!"); } else {        NSLog(@" ===== "); }

2.類CLass

在OC的一個類中，不允許重複定義一個函數，區分函數是否重複根據方法名，與接收參數無關。與java不同

pubic void getInfo(Animal a);public void getInfo(Person p);

//同一個方法getInfo:- (void)getInfo:(Animal)a;- (void)getInfo:(Person)p;

3.常見的集合

void arrayTest(){    NSArray *array = [NSArray arrayWithObjects:@"one", @"two", @"three", nil];    NSLog(@"len = %lu", [array count]);    for (NSObject *obj in array) {        NSLog(@"== %@", obj);    }    for (int i=0; i<[array count]; i++) {        NSLog(@"%@", [array objectAtIndex:i]);    }    //寫進檔案,atomically是否先將檔案儲存至臨時檔案中，待儲存成功之後，再與原始檔案替換，是一種安全機制。    [array writeToFile:@"/Users/zf/Desktop/1.txt" atomically:YES];    //讀取檔案    NSArray *arr = [NSArray arrayWithContentsOfFile:@"/Users/zf/Desktop/1.txt"];    NSLog(@"len3 = %lu", [arr count]);    }

void mutableArrayTest(){    NSMutableArray *array = [NSMutableArray arrayWithCapacity:3];    [array addObject:@"one"];    [array addObject:@"two"];    [array addObject:@"three"];    [array addObject:@"two1"];        NSLog(@"len = %lu", [array count]);    [array removeObjectAtIndex:3];    NSLog(@"len = %lu", [array count]);        NSEnumerator *e = [array objectEnumerator];    NSString *x;    while (x = [e nextObject]) {        NSLog(@"x == %@", x);    }    NSEnumerator *e1 = [array reverseObjectEnumerator];}

void dictTest(){    NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil];    NSLog(@"%@", [dict objectForKey:@"key2"]);        NSMutableDictionary *d = [NSMutableDictionary dictionaryWithCapacity:3];        [d setObject:@"wwwwww" forKey:@"key1"];    [d removeObjectForKey:@"key1"];    NSLog(@"%lu, key1=%@", [d count], [d objectForKey:@"key1"]);}

NSArray：有序集合，元素在一個整塊的記憶體中並按序排列；

NSSet：無序集合，散列儲存。
讀developer.apple關於NSSet的解釋：You can use sets as an alternative to arrays when the order of elements isn’t important and performance in testing whether an object is contained in the set is a consideration—while arrays are ordered, testing for membership is slower than with sets.
搜尋一個元素，NSSet的效率會比NSArray高。為什麼呢？原理比較簡單：NSSet中元素的儲存和訪問都是一個hash的過程。比如你要儲存元素A，一個hash演算法直接就能直接找到A應該儲存的位置；同樣，當你要訪問A時，一個hash過程就能找到A儲存的位置。而對於NSArray，若想知道A到底在不在數組中，則需要一個一個元素比較，顯然效率不高。

4.NSString

void stringTest(){    NSString *str = [NSString stringWithFormat:@"aa,bb,cc,"];    NSArray *array = [str componentsSeparatedByString:@","];    NSLog(@"len = %lu", [array count]);        NSLog(@"%@", [array componentsJoinedByString:@"-"]);}