from:http://blog.csdn.net/wherejaly/article/details/5538248

如果要从data中或者file中读取数据并包装成UIImage可以使用+ p_w_picpathWithData: 和+ p_w_picpathWithContentsOfFile: 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


[cpp]view plaincopy

  1. / Create paths to output p_w_picpaths

  2. NSString *pngPath = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/Test.png"];

  3. NSString *jpgPath = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/Test.jpg"];

  5. // Write a UIImage to JPEG with minimum compression (best quality)

  6. // The value 'p_w_picpath' must be a UIImage object

  7. // The value '1.0' represents p_w_picpath compression quality as value from 0.0 to 1.0

  8. [UIImageJPEGRepresentation(p_w_picpath, 1.0) writeToFile:jpgPath atomically:YES];

  10. // Write p_w_picpath to PNG

  11. [UIImagePNGRepresentation(p_w_picpath) writeToFile:pngPath atomically:YES];

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

  15. // Create file manager

  16. NSError *error;

  17. NSFileManager *fileMgr = [NSFileManager defaultManager];

  19. // Point to Document directory

  20. NSString *documentsDirectory = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];

  22. // Write out the contents of home directory to console

  23. NSLog(@"Documents directory: %@", [fileMgr contentsOfDirectoryAtPath:documentsDirectory error:&error]);