iphone 判断文件是否存在，获得图片资源

•     在iphone上使用NSFileManager判断文件是否存在时，有时总是返回NO.

                原因可能是：NSFileManager没有初始化。

•    切换路径：

                NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
                NSString *documentsDirectory = [paths objectAtIndex:0];//获得需要的路径
                NSLog(@"cur: %@",documentsDirectory);
                //切换成当前目录
                [fileManager changeCurrentDirectoryPath:[documentsDirectory stringByExpandingTildeInPath]];

 

• 浏览document下所有图片资源

    #define DOCUMENTS_FOLDER [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"]
    NSArray *fileList = [[[NSFileManager defaultManager] directoryContentsAtPath:DOCUMENTS_FOLDER]
                pathsMatchingExtensions:[NSArray arrayWithObject:@"png"]] ;

• 得到图片中的某一部分：

    UIImage *image = [UIImage imageNamed:filename];
    CGImageRef imageRef = image.CGImage;

    CGRect rect = CGRectMake(origin.x, origin.y ,size.width, size.height);

    CGImageRef imageRefRect = CGImageCreateWithImageInRect(imageRef, rect);

    UIImage *imageRect = [[UIImage alloc] initWithCGImage:imageRefRect];