将图像转换为 NSData 并返回为 nil

Question

当我做的时候

UIImage *photo = [UIImage imageNamed:@"sample_thumbnail.png"];
self.thumbnail.image = photo;

我看到了缩略图，它是 PNG，很好。当我转换为 NSData 并返回时：

UIImage *photo = [UIImage imageNamed:@"sample_thumbnail.png"];
NSData *data = UIImagePNGRepresentation(photo);
self.photoData = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
self.thumbnail.image = [UIImage imageWithData:[self.photoData dataUsingEncoding:NSUTF8StringEncoding]];

self.photoData 为零。

为什么会这样？

Answer 1

我认为问题在于您从 NSData 实例创建图像的方式。试试这个：

UIImage *photo = [UIImage imageNamed:@"sample_thumbnail.png"];
NSData *data = UIImagePNGRepresentation(photo);
UIImage *image = [UIImage imageWithData:data];

__UPDATE__

以下摘自this post

- (NSString *)imageToNSString:(UIImage *)image
{
    NSData *imageData = UIImagePNGRepresentation(image);

    return [imageData base64EncodedStringWithOptions:NSDataBase64Encoding64CharacterLineLength];
}

- (UIImage *)stringToUIImage:(NSString *)string
{
    NSData *data = [[NSData alloc]initWithBase64EncodedString:string
                                                  options:NSDataBase64DecodingIgnoreUnknownCharacters];

    return [UIImage imageWithData:data];
}