Question

哪一个在运行时更好： 1）在sqlite中保存大小为250X120的图像。 2）在文档目录中保存相同大小的图像。在两个三个地方app需要这些保存的图像显示在控件中。此外，我要求最多显示20张图像。

Answer 1

第二种选择远胜于第一种选择。完成第二部分的使用：

- (void)saveImage:(UIImage*)image:(NSString*)imageName
{
    NSData *imageData = UIImagePNGRepresentation(image); //convert image into .png format.

    NSFileManager *fileManager = [NSFileManager defaultManager];//create instance of NSFileManager

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); //create an array and store result of our search for the documents directory in it

    NSString *documentsDirectory = [paths objectAtIndex:0]; //create NSString object, that holds our exact path to the documents directory

    NSString *fullPath = [documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.png", imageName]]; //add our image to the path 

    [fileManager createFileAtPath:fullPath contents:imageData attributes:nil]; //finally save the path (image)

    NSLog(@"image saved");
}

Answer 2

+1 M.Sharjeel - 我们使用的通常是半混合，我们将拥有一个Core Data对象（由手机/平板电脑上的sqlite支持），其中包含有关快速搜索的文件的元数据，然后将NSString存储到documentsDirectory中的路径。

Answer 3

如果采用文档目录方法，这是完成它的好方法。

-(void) saveImage:(UIImage *)image withFileName:(NSString *)imageName ofType:(NSString *)extension inDirectory:(NSString *)directoryPath {
    if ([[extension lowercaseString] isEqualToString:@"png"]) {
        [UIImagePNGRepresentation(image) writeToFile:[directoryPath stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.%@", imageName, @"png"]] options:NSAtomicWrite error:nil];
    } else if ([[extension lowercaseString] isEqualToString:@"jpg"] || [[extension lowercaseString] isEqualToString:@"jpeg"]) {
        [UIImageJPEGRepresentation(image, 1.0) writeToFile:[directoryPath stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.%@", imageName, @"jpg"]] options:NSAtomicWrite error:nil];
    } else {
        ALog(@"Image Save Failed\nExtension: (%@) is not recognized, use (PNG/JPG)", extension);
    }
}

要保存图像，只需按以下步骤操作：

NSString * path = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
[self saveImage:yourImage withFileName:@"Your Image Name" ofType:@"png" inDirectory:path];

要加载图像，请实现此方法：

-(UIImage *) loadImage:(NSString *)fileName ofType:(NSString *)extension inDirectory:(NSString *)directoryPath {

    UIImage * result = [UIImage imageWithContentsOfFile:[NSString stringWithFormat:@"%@/%@.%@", directoryPath, fileName, extension]];

    return result;
}

然后像这样使用它：

NSString * path = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
yourImage.image = [self loadImage:@"Your Image Name" ofType:@"png" inDirectory:path];

或者您可以简单地将图像设置为等于此方法返回的内容而不是创建方法：

NSString * path = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
yourImage.image = [UIImage imageWithContentsOfFile:[NSString stringWithFormat:@"%@/Your Image Name.png", path]];

在iphone应用程序中运行时保存图像

3 个答案: