iOS---如何截图，如何将图片保存到相册

- (void)viewDidLoad {
    [super viewDidLoad];
    UIButton * btn = [UIButton buttonWithType:UIButtonTypeContactAdd];
    btn.frame =CGRectMake(30, 30, 30, 30);
    [self.view addSubview:btn];
    [btn addTarget:self action:@selector(btnClick:) forControlEvents:UIControlEventTouchUpInside];
}
-(void)btnClick:(UIButton *)sender
{
    [self savePhoto];
}
// 保存图片到相册功能，ALAssetsLibraryiOS9.0 以后用photoliabary 替代，
-(void)savePhoto
{
    UIImage * image = [self captureImageFromView:self.view];
    ALAssetsLibrary * library = [ALAssetsLibrary new];
    NSData * data = UIImageJPEGRepresentation(image, 1.0);
    [library writeImageDataToSavedPhotosAlbum:data metadata:nil completionBlock:nil];
}
//截图功能
-(UIImage *)captureImageFromView:(UIView *)view
{
    CGRect screenRect = [view bounds];
    UIGraphicsBeginImageContext(screenRect.size);
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    [view.layer renderInContext:ctx];
    UIImage * image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}