iphone 怎样将UIImage对象保存到JPG或者PNG文件中？

我们都知道如果要从data中或者file中读取数据并包装成UIImage可以使用+ imageWithData: 和+ imageWithContentsOfFile: 但如果想把UIImage的图片数据写入到jpg或者png格式的文件中呢？答案是UIImageJPEGRepresentation，请看如下代码

 / Create paths to output images
 NSString  *pngPath = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/Test.png"];
 NSString  *jpgPath = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/Test.jpg"];

 // Write a UIImage to JPEG with minimum compression (best quality)
 // The value 'image' must be a UIImage object
 // The value '1.0' represents image compression quality as value from 0.0 to 1.0
 [UIImageJPEGRepresentation(image, 1.0) writeToFile:jpgPath atomically:YES];

 // Write image to PNG
 [UIImagePNGRepresentation(image) writeToFile:pngPath atomically:YES];

 // Let's check to see if files were successfully written...

 // Create file manager
 NSError *error;
 NSFileManager *fileMgr = [NSFileManager defaultManager];

 // Point to Document directory
 NSString *documentsDirectory = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];

 // Write out the contents of home directory to console
 NSLog(@"Documents directory: %@", [fileMgr contentsOfDirectoryAtPath:documentsDirectory error:&error]);