IOS_OC _ basic syntax

1. YES and NO

Object-c provides the BOOL type, but this BOOL type is not the same as that in C ++: In C ++, all non-0 values are true, the value 0 is false. However, in Object-c, 1 is true and the macro is defined as YES = 1, 0 is false, and the macro is defined as NO = 0.

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

2. CLass

In an OC class, you cannot define a function repeatedly to identify whether the function is repeated based on the method name, regardless of the receiving parameter. Different from java

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

// The same method getInfo:-(void) getInfo :( Animal) a;-(void) getInfo :( Person) p;

3. Common collections

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]);} // write it into the file. Whether atomically saves the file to the temporary file first. After the file is saved successfully, it is replaced with the original file. This is a security mechanism. [Array writeToFile: @ "/Users/zf/Desktop/1.txt" atomically: YES]; // read the file 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: an ordered set of elements in the memory of a whole block and arranged in order;

NSSet: unordered set, hashed storage.
Read developer. apple's explanation of NSSet: 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.
When you search for an element, NSSet is more efficient than NSArray. Why? The principle is relatively simple: the storage and access of elements in NSSet are a hash process. For example, if you want to store element A, A hash algorithm can directly locate the location where A should be stored. Similarly, when you want to access, A hash process can locate the storage location of. For NSArray, if you want to know whether A is not in the array, You need to compare the elements one by one. Obviously, the efficiency is not high.

4. NSString

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