将某视图View转换为UIImage

+ (UIImage *)getSharedScreenView{

    UIWindow *screenWindow = [[UIApplication sharedApplication]keyWindow];
    ScreenView *currentView = [[[self class] alloc] init];
    currentView.frame = screenWindow.bounds;
    [screenWindow addSubview:currentView];

//UIGraphicsBeginImageContext() 图片会失真模糊
    UIGraphicsBeginImageContextWithOptions(screenWindow.frame.size, NO, 0.0);//图片不模糊
    [screenWindow.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage* viewImage =UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    [currentView removeFromSuperview];
    //UIImageWriteToSavedPhotosAlbum(viewImage,nil,nil,nil); //写入到相册
    return viewImage;
}