使用较小的 UIImage 为 UIActivityViewController 设置缩略图

Question

我想设置一个较小的特定缩略图，但仍为我正在分享的活动项目使用高质量的图像。我的问题是分享大图时，生成缩略图需要时间，这可能会在分享到某些应用时出现问题。

例如，如果我展示我的 UIActivity 控制器并选择 Messenger，

我没有时间让我的缩略图加载，选择一个人并点击发送，它永远不会完成发送，我需要取消。

只有等待缩略图生成，然后点击发送，一切都会正常进行。

在这种情况下，“照片”是高质量的UIImage，但是如何设置缩略图以避免在UIActivityViewController出现时生成一个高质量的图像呢？

let activity = UIActivityViewController(activityItems: [photo], applicationActivities: nil)

UIApplication.topViewController?.present(activity, animated: true, completion: nil)

---

有一个关于缩略图的文档，但我不确定如何实现它，或者在这种情况下是否有帮助：https://developer.apple.com/documentation/uikit/uiactivityitemsource/1620462-activityviewcontroller

另外，我阅读了 UIActivityItemProvider，它指出：

例如，您可以使用提供者对象来表示需要处理的大型视频文件，然后才能将其共享到用户的社交媒体帐户。

这是否意味着它可以推迟显示我想与之共享图像的应用程序，直到它准备好？我继承了 UIActivityItemProvider，并传递了一个缩略图，但它似乎没有任何效果。我要么做错了什么，要么这不是我想要使用的。

我的子类 UIActivityItemProvider：

class CustomProvider : UIActivityItemProvider {

    var image : UIImage!

    init(placeholderItem: AnyObject, image : UIImage) {
        super.init(placeholderItem: placeholderItem)
        self.image = image
    }

    override var item: Any {
        return self.image!
    }
}

我有一个共享功能，它是一个扩展。我创建了一个缩略图图像并将其传递给 CustomProvider 函数中的 placeholderItem：

extension Equatable {
    func share() {

        let imageData = (self as! UIImage).pngData()!
        let options = [
            kCGImageSourceCreateThumbnailWithTransform: true,
            kCGImageSourceCreateThumbnailFromImageAlways: true,
            kCGImageSourceThumbnailMaxPixelSize: 300] as CFDictionary
        let source = CGImageSourceCreateWithData(imageData as CFData, nil)!
        let imageReference = CGImageSourceCreateThumbnailAtIndex(source, 0, options)!
        let thumbnail = UIImage(cgImage: imageReference)


        let firstActivityItem = CustomProvider(placeholderItem: thumbnail, image: self as! UIImage)

        let activity = UIActivityViewController(activityItems: [firstActivityItem], applicationActivities: nil)

        UIApplication.topViewController?.present(activity, animated: true, completion: nil)
    }
}

Answer 1

让ActivityViewController 为您完成工作。

func activityViewController(activityViewController: UIActivityViewController, thumbnailImageForActivityType activityType: String?, suggestedSize size: CGSize) -> UIImage? {
    let maxSize = [size.width, size.height].max()
    let imageData = (self as! UIImage).pngData()!
    let options = [
            kCGImageSourceCreateThumbnailWithTransform: true,
            kCGImageSourceCreateThumbnailFromImageAlways: true,
            kCGImageSourceThumbnailMaxPixelSize: maxSize as Any] as CFDictionary
    let source = CGImageSourceCreateWithData(imageData as CFData, nil)!
    let imageReference = CGImageSourceCreateThumbnailAtIndex(source, 0, options)!
    let thumbnail = UIImage(cgImage: imageReference)
    return thumbnail
}

let activity = UIActivityViewController(activityItems: [photo], applicationActivities: nil)

UIApplication.topViewController?.present(activity, animated: true, completion: nil)

我认为您不需要特定的ActivityType，所以这是假设所有活动。

另外，请确保扩展 UIActivityItemSource。

我使用this SO Post 作为参考。

编辑1

子类UIActivityItemSource

class MyActivityType:NSObject, UIActivityItemSource {

    var image:UIImage!
    var placeholderImage:UIImage!

    convenience init(image:UIImage, placeholderImage:UIImage) {
        self.init()
        self.image = image
        self.placeholderImage = placeholderImage
    }

    //Placeholder - we use `return UIImage()` so the sheet knows it is an image
    func activityViewControllerPlaceholderItem(_ activityViewController: UIActivityViewController) -> Any {
        return self.placeholderImage
    }

    //Actual item you are sending
    func activityViewController(_ activityViewController: UIActivityViewController, itemForActivityType activityType: UIActivity.ActivityType?) -> Any? {
        return self.image
    }

    //Thumbnail - Apple states that `For activities that support a preview image, returns a thumbnail preview image for the item.` but since you are pushing an image for your item, should be good to go.
    func activityViewController(_ activityViewController: UIActivityViewController, thumbnailImageForActivityType activityType: UIActivity.ActivityType?, suggestedSize size: CGSize) -> UIImage? {
        return self.placeholderImage
    }
}

我没有收到任何错误 - 但我无法运行它，所以我没有看到任何运行时错误。

然后你就可以这样发送了--

DispatchQueue.global(qos: .userInitiated).async { [weak self] in

    let imageData = (self! as! UIImage).pngData()!
    let options = [
        kCGImageSourceCreateThumbnailWithTransform: true,
        kCGImageSourceCreateThumbnailFromImageAlways: true,
        kCGImageSourceThumbnailMaxPixelSize: 300] as CFDictionary
    let source = CGImageSourceCreateWithData(imageData as CFData, nil)!
    let imageReference = CGImageSourceCreateThumbnailAtIndex(source, 0, options)!
    let thumbnail = UIImage(cgImage: imageReference)

    //Back to main thread
    DispatchQueue.main.async { [weak self] in

        //Remove loading indicator
        let firstActivityItem = MyActivityType(image: (self! as! UIImage), placeholderImage: thumbnail)

        let activity = UIActivityViewController(activityItems: [firstActivityItem], applicationActivities: nil)

        UIApplication.topViewController?.present(activity, animated: true, completion: nil)
    }
}

Answer 2

您可以在应用程序中生成低质量图像并在 UIActivityViewController 中引用该 url

let activity = UIActivityViewController(
activityItems: ["Some description", url],
applicationActivities: nil)

您可以使用以下方法生成可以稍后保存在本地的低质量图像：

NSData * UIImageJPEGRepresentation(UIImage *image, CGFloat compressionQuality);

... 或参考以下帖子了解更多技术知识和方法： http://vocaro.com/trevor/blog/2009/10/12/resize-a-uiimage-the-right-way/

学分。从以下位置提取的材料：

• https://www.raywenderlich.com/813044-uiactivityviewcontroller-tutorial-sharing-data
• https://developer.apple.com/documentation/uikit/1624115-uiimagejpegrepresentation
• https://thomasguenzel.com/blog/2015/04/16/uiactivityviewcontroller-nsdata-with-filename/