1.建立字串
（1）常量字串
複製代碼 代碼如下:
NSString *string = @"i am an iOSDevTip!";
（2）常用建立方法
複製代碼 代碼如下:
NSString *string = [[NSString alloc] init];
string = @"i am an iOSDevTip too!";
（3）用initWithString建立字串
複製代碼 代碼如下:
NSString *string = [[NSString alloc] initWithString:@"iOSDevTip is here!"];
2.格式化建立字串
（1）int格式化字串
複製代碼 代碼如下:
int age = 20;
NSString *personAge = [NSString stringWithFormat:@"this person age is %d",age];
既然int格式化字串，那麼float、double等，也可以格式化字串。
（2）NSString格式化字串
複製代碼 代碼如下:
NSString *name = @"iOSDevTip";
NSString *personName = [NSString stringWithFormat:@"this person name is %@",name];
3.字串比較
（1）isEqualToString方法比較
複製代碼 代碼如下:
NSString *stingOne = @"This is an iOSDevTip!";
NSString *stringTwo = @"This is an iOSDevTip!";
BOOL result = [stingOne isEqualToString:stringTwo];
（2）compare方法比較
複製代碼 代碼如下:
BOOL result = [stingOne compare:stringTwo] == NSOrderedSame;
compare:方法傳回值類型為NSComparisonResult。而NSComparisonResult有下面幾個枚舉值。
複製代碼 代碼如下:
typedef NS_ENUM(NSInteger, NSComparisonResult) {NSOrderedAscending = -1L, NSOrderedSame, NSOrderedDescending};
4.字串大小寫轉換
（1）小寫轉大寫
複製代碼 代碼如下:
NSString *string = @"This is an iOSDevTip!";
[string lowercaseString];
（2）大寫轉小寫
複製代碼 代碼如下:
NSString *string = @"This is an iOSDevTip!";
[string uppercaseString];
（3）首字母大寫
複製代碼 代碼如下:
NSString *string = @"ligang";
NSLog(@"string: %@",[string capitalizedString]);
列印：
2015-07-16 23:06:11.652 iOSStrongDemo[10279:3062010] string: Ligang
5.截取字串
（1）substringToIndex截取字串
複製代碼 代碼如下:
NSString *string = @"This is a operation string!";
NSString *subToString = [string substringToIndex:6];
（2）截取的subToString為This i
substringFromIndex截取字串
複製代碼 代碼如下:
NSString *subFromString = [string substringFromIndex:6];
（3）截取的subFromString為s a operation string!
substringWithRange截取字串
複製代碼 代碼如下:
NSString *rangeString = [string substringWithRange:NSMakeRange(6, 3)];
截取的rangeString為s a!
6.判斷字串是否包含另一個字串
（1）rangeOfString判斷
複製代碼 代碼如下:
NSString *string1 = @"This is a iOSDevTip";
NSString *string2 = @"iOSDevTip";
NSRange range = [string1 rangeOfString:string2];
NSInteger location = range.location;
NSInteger leight = range.length;
NSString *logString = [[NSString alloc] initWithString:[NSString stringWithFormat:@"Location:%ld,Leight:%ld",location,leight]];
NSLog(@"logString:%@",logString);
列印出來：
iOSStrongDemo[8837:2221170] logString:Location:10,Leight:9
（2）判斷是否包含前尾碼
複製代碼 代碼如下:
NSString *string = @"I love China";
BOOL isHasI = [string hasPrefix:@"I"];
BOOL isHasChina = [string hasSuffix:@"China"];
7.分割字串
複製代碼 代碼如下:
NSString *string = @"This is a iOSDevTip";
NSArray *array = [string componentsSeparatedByString:@"a"];
NSString *string1 = [array objectAtIndex:0];
NSString *string2 = [array objectAtIndex:1];
NSLog(@"string1:%@ string2:%@",string1,string2);
列印：
2015-07-16 22:40:39.559 iOSStrongDemo[10165:3055448] string1:This is string2: iOSDevTip
8.插入字串
複製代碼 代碼如下:
NSMutableString *string = [[NSMutableString alloc] initWithString:@"I China"];
[string insertString:@"Love " atIndex:2];
NSLog(@"string: %@",string);
列印：
2015-07-16 22:44:10.706 iOSStrongDemo[10206:3057014] string: I Love China
（1）追加字串
複製代碼 代碼如下:
NSMutableString *string = [[NSMutableString alloc] initWithString:@"I Love "];
[string appendString:@"China"];
NSLog(@"string:%@",string);
列印：
2015-07-16 22:42:32.305 iOSStrongDemo[10189:3056410] string:I Love China
9.刪除字串
複製代碼 代碼如下:
NSMutableString *string = [[NSMutableString alloc] initWithString:@"I love China"];
[string deleteCharactersInRange:NSMakeRange(2, 4)];
NSLog(@"String1: %@",string);
列印：
2015-07-16 22:46:58.437 iOSStrongDemo[10219:3057749] String1: I China
10.替換字串
複製代碼 代碼如下:
NSString *string = @"I love China";
NSString *replaceString = [string stringByReplacingOccurrencesOfString:@"love" withString:@"like"];
NSLog(@"replaceString: %@",replaceString);
列印：
2015-07-16 22:56:07.405 iOSStrongDemo[10236:3059503] replaceString: I like China
11.去除字串首尾的空格和分行符號
複製代碼 代碼如下:
NSString *string = @" I love China ";
NSString *text = [string stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];
NSLog(@"text:%@",text);
列印：
2015-07-16 23:00:47.845 iOSStrongDemo[10265:3061013] text:I love China
