iOS类型的转换

1.NSData和NSString的转换:

- (void)viewDidLoad {
    [super viewDidLoad];

    // 字符串
    NSString *str = @"";
    NSLog(@"str = %@",str);

    // NString -> NSData
    NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];
    NSLog(@"Data = %@",data);

    // NSData -> NString
    NSString *dataStr = [[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding];
    NSLog(@"dataStr = %@",dataStr);

}

2.图片和字符串的转换:

//图片转字符串
-(NSString *)UIImageToBase64Str:(UIImage *) image
{
NSData *data = UIImageJPEGRepresentation(image, 1.0f);
NSString *encodedImageStr = [data base64EncodedStringWithOptions:NSDataBase64Encoding64CharacterLineLength];
return encodedImageStr;
}  

//字符串转图片
-(UIImage *)Base64StrToUIImage:(NSString *)_encodedImageStr
{
    NSData *_decodedImageData   = [[NSData alloc] initWithBase64Encoding:_encodedImageStr];
    UIImage *_decodedImage      = [UIImage imageWithData:_decodedImageData];
    return _decodedImage;
}

3.有解决NSData转NSString为nil的解决方法,是使用了一个扩展,不过,我总之是没有成功的,还是nil,难道是对图片压缩转Data了?

这里有知道的大神可以告诉我哟!!特别感谢了!!

扩展如以下所示:

//
//  NSData+UTF8.m
//  zichan
//
//  Created by 思 彭 on 16/11/9.
//  Copyright © 2016年 Mike. All rights reserved.
//

#import "NSData+UTF8.h"

@implementation NSData (UTF8)

- (NSData *)UTF8Data
{
    //保存结果
    NSMutableData *resData = [[NSMutableData alloc] initWithCapacity:self.length];

    //无效编码替代符号(常见 � □ ?)
    NSData *replacement = [@"�" dataUsingEncoding:NSUTF8StringEncoding];

    uint64_t index = ;
    const uint8_t *bytes = self.bytes;

    while (index < self.length)
    {
        uint8_t len = ;
        uint8_t header = bytes[index];

        //单字节
        if ((header&0x80) == )
        {
            len = ;
        }
        //2字节(并且不能为C0,C1)
        else if ((header&0xE0) == 0xC0)
        {
            if (header != 0xC0 && header != 0xC1)
            {
                len = ;
            }
        }
        //3字节
        else if((header&0xF0) == 0xE0)
        {
            len = ;
        }
        //4字节(并且不能为F5,F6,F7)
        else if ((header&0xF8) == 0xF0)
        {
            if (header != 0xF5 && header != 0xF6 && header != 0xF7)
            {
                len = ;
            }
        }

        //无法识别
        if (len == )
        {
            [resData appendData:replacement];
            index++;
            continue;
        }

        //检测有效的数据长度(后面还有多少个10xxxxxx这样的字节)
        uint8_t validLen = ;
        while (validLen < len && index+validLen < self.length)
        {
            if ((bytes[index+validLen] & 0xC0) != 0x80)
                break;
            validLen++;
        }

        //有效字节等于编码要求的字节数表示合法,否则不合法
        if (validLen == len)
        {
            [resData appendBytes:bytes+index length:len];
        }else
        {
            [resData appendData:replacement];
        }

        //移动下标
        index += validLen;
    }

    return resData;
}
@end