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 1.常用功能使用
 
  
1)初始化
NSString *astring = @"This is a String!"; //固定字符串 NSString *str = [NSString stringWithFormat:@"asd%d%@",123,@"ttt"]; //拼组字符串
2)截取
NSString *str = [@"asd" substringFromIndex:1]; //从第几位开始截到最后 NSString *str1 = [str substringToIndex:1]; //从开始位置截到第几位 NSString *str = [[@"asd" substringFromIndex:1] substringToIndex:1]; //从第几位开始截几个字符
3)分解
NSArray *array = [@"asd|tes|mmm" componentsSeparatedByString:@"|"];
4)查找
 NSRange range = [@"12rasd124" rangeOfString:@"asd"];
 if (range.location != NSNotFound) {
      NSString *str = [@"12rasd124" substringWithRange:range];
 }  
5)替换
NSString *str = [@"asdasd" stringByReplacingOccurrencesOfString:@"asd" withString:@"ok"];
6)路径相关
[filepath lastPathComponent]; //获得文件名 [filepath pathExtension]; //获得文件扩展名 [filtpaht stringByDeletingLastPathComponent]; //获得文件的所在文件夹路径 [filtpath stringByDeletingPathExtension]; //获得去除扩展名的文件路径
7)字符串是否为空
if (str.lenght > 0) //不管str是不是nil都可以这么判断
8)字符串比较
if ([@"asd" isEqualToString:@"asd"]) {
   
}  
9)字符串比大小
    NSString *stra = @"asd";
    NSString *strb = @"dfs";
    NSComparisonResult result = [stra compare:strb];
    if (result == NSOrderedSame) {
        
    } else if (result == NSOrderedAscending) {
    
    } else {
        
    } 
 
 
2.常用扩展功能(类别扩展)
 1)md5
 
 
- (NSString *)md5HexDigest
{
    const char* str = [self UTF8String];
    unsigned char result[CC_MD5_DIGEST_LENGTH];
    CC_MD5(str, strlen(str), result);
    NSMutableString *ret = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH];
    
    for(int i = 0; i<CC_MD5_DIGEST_LENGTH; i++) {
        [ret appendFormat:@"%02X",result[i]];
    }
    return ret;
    
}  
2)urlEncode
- (NSString *)stringEncode {
    NSString *encodedString = (NSString *)CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault, (CFStringRef)self, NULL, CFSTR(":/?#[]@!$ &'()*+,;=\"<>%{}|\\^~`"), kCFStringEncodingUTF8));
    return encodedString;
}
- (NSString *)stringDecode {
    NSString *result = [(NSString *)self stringByReplacingOccurrencesOfString:@"+" withString:@" "];
    result = [result stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
    return result;
}  
3)sizeFromFont
- (CGSize)boundingRectWithSize:(CGSize)size
                  withTextFont:(UIFont *)font {
    if ([self isEqualToString:@""]) {
        return CGSizeMake(0, 0);
    }
    NSMutableParagraphStyle *paragraphStyle = [[NSMutableParagraphStyle alloc] init];
    paragraphStyle.lineBreakMode = NSLineBreakByWordWrapping;
    paragraphStyle.lineSpacing = 0;
    NSDictionary *attributes = @{NSFontAttributeName:font, NSParagraphStyleAttributeName:paragraphStyle.copy};
    
    return [self boundingRectWithSize:size options:NSStringDrawingUsesLineFragmentOrigin attributes:attributes context:nil].size;
}  
 4) 是否是邮箱格式
 
 
- (BOOL)isEmail
{
    NSString *emailRegEx =  
	@"(?:[a-z0-9!#$%\\&'*+/=?\\^_`{|}~-]+(?:\\.[a-z0-9!#$%\\&'*+/=?\\^_`{|}"  
	@"~-]+)*|\"(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21\\x23-\\x5b\\x5d-\\" 
	@"x7f]|\\\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])*\")@(?:(?:[a-z0-9](?:[a-"  
	@"z0-9-]*[a-z0-9])?\\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\\[(?:(?:25[0-5"  
	@"]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-"  
	@"9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21"  
	@"-\\x5a\\x53-\\x7f]|\\\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])+)\\])";  
	
    NSPredicate *regExPredicate = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", emailRegEx];  
    return [regExPredicate evaluateWithObject:[self lowercaseString]];  
}  
 5) Base64
 
 
- (NSString *)base64 {
    // Create NSData object
    NSData *nsdata = [self dataUsingEncoding:NSUTF8StringEncoding];
    
    // Get NSString from NSData object in Base64
    NSString *base64Encoded = [nsdata base64EncodedStringWithOptions:0];
    
    // Print the Base64 encoded string
    return base64Encoded;
}
- (NSString *)base64Decoded {
    // NSData from the Base64 encoded str
    NSData *nsdataFromBase64String = [[NSData alloc] initWithBase64EncodedString:self options:0];
    
    // Decoded NSString from the NSData
    NSString *base64Decoded = [[NSString alloc] initWithData:nsdataFromBase64String encoding:NSUTF8StringEncoding];
   
    return base64Decoded;
} 
 
 
