iOS字符串NSString常用方法

//1）字面量，它是常量字符串，存儲常量區
NSString *str=@"hello";
//2）通過快捷構造法，存儲堆區
NSString *str = [NSString stringWithFormat:@"hello %@", @"world"];
//3）初始化方法
NSString *str = [[NSString alloc] initWithFormat:@"%@",@"hello"];

NSString *str=@"hello";
long length = str.length;

NSString *str=@"hello";

/*從索引字符串開始截取，直到字符串末尾，包含索引上的字符*/
NSString *strSub = [str substringFormIndex:2];

/*從字符串開頭開始截取，直到索引位置，不包含索引上的字符*/
NSString *strSubT = [str substringToIndex:2];

/*從哪個位置開始，截取多長*/
NSRange range = {2,4};
NSString *strSubR = [str substringWithRange:range];

/*獲取某個子串所在的區域*/
NSRange rangeS = [str rangeOfString"@"el"];

/*計算文本大小*/
CGSize maxSize = CGSizeMake(MAXFLOAT, MAXFLOAT);/*width與height都不限制*/
CGSize nameSize = [self.microBlogModel.name boundingRectWithSize:maxSize options:NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName:[UIFont systemFontOfSize:15]} context:nil].size;

/*單詞首字母轉大寫*/
[str capitalizedString];

/*字符替換*/
NSString *newStr = [str stringByReplacingOccurencesOfString:@"ll" withString:@"al"];

/*使用某個字符串替換掉原來字符串中某個區間的字符串*/
NSRange range = [str rangeOfString:@"ll"];
NSString *newStr = [str stringByReplacingCharactersInRange:range withSring:@"hi"];

/*刪除原字符串中的所有指定字符串*/
NSString *newStr = [str stringByReplacingOccurencesOfString:@"ll" withString:@""];

/*去掉兩頭空格*/
NSString *newStr = [str stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];

/*在原來路徑上拼接一個路徑*/
NSString *path = @"/Users/dengwei";
path = [path stringByAppendingPathComponent:@"Desktop"];

/*獲取擴展名*/
NSString *path = @"/Users/dengwei/Desktop/apple.txt";
path = [path stringByDeletingPathExtension];
path = [path stringByAppendingPathExtension:@"png"];

/*把字符串寫入文件*/
NSString *str = @"today is cold!";
NSString *path = @"/Users/dengwei/Desktop/apple.txt";
NSError *error;
BOOL isSuccess = [str writeToFile:path atomically:YES encoding:NSUTF8StringEncoding error:&error];

/*讀取文件*/
NSString *string = [NSString stringWithContentsOfFile:path encoding:NSUTF8StringEncoding error:&error];

/*
URL：Uniform Resource Locator 統一資源定位符
URL：格式  協議頭://主機名稱/資源路徑
http://www.baidu.com/some/images/pic.png
404：沒有找到資源
*/
NSString *str = @"today is cold!";
/*url路徑中不支持中文，若是有中文則需將中文轉碼*/
NSURL *url =  [NSURL URLWithString:@"file:///Users/dengwei/Desktop/apple.txt"];

/*將中文轉碼*/
NSString *url_cn =  @"file:///Users/dengwei/Desktop/中文.txt";
/*編碼，把UTF8編碼的字符串編碼成URL中可用的字符串*/
url_cn = [url_cn stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
/*解碼，把URL中可用的字符串編碼的字符串解碼成UTF8編碼的字符串*/
url_cn = [url_cn stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

url_cn = [NSURL URLWithString:url_cn];
NSError *error;
/*寫入*/
BOOL isSuccess = [str writeToURL:url atomically:YES encoding:NSUTF8StringEncoding error:&error];
/*讀取*/
NSString *string = [str stringWithContentsOfURL:url atomically:YES encoding:NSUTF8StringEncoding error:&error];

NSMutableString *strM = [NSMutableString string];
/*Capacity表示容量，可以容納多少字符，如果超過這個存儲空間，就會擴展它*/
NSMutableString *strM = [NSMutableString stringWithCapacity:10];