iOS - UIImageWriteToSavedPhotosAlbum

iOS - UIImageWriteToSavedPhotosAlbum

提问by user682765

I wanted to use the following void API to write a captured image to the photo album but I am not very clear about 2 of the parameters

我想使用以下void API将捕获的图像写入相册，但我对其中2个参数不是很清楚

UIImageWriteToSavedPhotosAlbum (
   UIImage  *image,
   id       completionTarget,
   SEL      completionSelector,
   void     *contextInfo
);

From the explanation from ADC:

来自ADC的解释：

completionTarget:optional; the object whose selector should be called after the image has been written to the Camera Roll album.

completionTarget:可选的; 将图像写入相机胶卷相册后应调用其选择器的对象。

completionSelector:the method selector of the completionTarget object. This optional method should conform to the following signature:

completionSelector:completionTarget 对象的方法选择器。此可选方法应符合以下签名：

- (void)image:(UIImage *)image didFinishSavingWithError:(NSError *)error contextInfo: (void *) contextInfo;

What is the significance of completionTargethere? Can someone explain with an example how this parameter should be used? Or any resource which can guide me through it.

completionTarget这里有什么意义？有人可以用一个例子来解释这个参数应该如何使用吗？或者任何可以指导我完成它的资源。

回答by AliSoftware

• The completionSelectoris the selector (method) to call when the writing of the image has finished.
• The completionTargetis the object on which to call this method.

• 在completionSelector当图像的写入已经完成的是选择器（方法），以调用。
• 的completionTarget是在其上调用此方法的对象。

Generally:

一般来说：

• Either you don't need to be notified when the writing of the image is finished (in many cases that's not useful), so you use nilfor both parameters
• Or you really want to be notified when the image file has been written to the photo album (or ended up with a writing error), and in such case, you generally implement the callback (= the method to call on completion) in the same class that you called the UIImageWriteToSavedPhotosAlbumfunction from, so the completionTargetwill generally be self

• 要么不需要在图像写入完成时收到通知（在许多情况下这没有用），因此您使用nil两个参数
• 或者你真的想在图像文件写入相册时得到通知（或以写入错误结束），在这种情况下，你通常在同一个地方实现回调（=完成时调用的方法）您UIImageWriteToSavedPhotosAlbum从中调用函数的类，因此completionTarget通常是self

As the documentation states, the completionSelectoris a selector representing a method with the signature described in the documentation, so it has to have a signature like:

正如文档所述，completionSelector是一个选择器，表示具有文档中描述的签名的方法，因此它必须具有如下签名：

- (void)image:(UIImage *)image didFinishSavingWithError:(NSError *)error contextInfo: (void *) contextInfo;

It does not have to have this exact name, but it has to use the same signature, namely take 3 parameters (the first being an UIImage, the second an NSErrorand the third being of void*type) and return nothing (void).

它不必具有这个确切的名称，但必须使用相同的签名，即接受 3 个参数（第一个是 an UIImage，第二个是 an NSError，第三个是void*类型）并且不返回任何内容 ( void)。

---

---

Example

例子

You may for example declare and implement a method that you could call anything like this :

例如，您可以声明并实现一个方法，您可以调用这样的方法：

- (void)thisImage:(UIImage *)image hasBeenSavedInPhotoAlbumWithError:(NSError *)error usingContextInfo:(void*)ctxInfo {
    if (error) {
        // Do anything needed to handle the error or display it to the user
    } else {
        // .... do anything you want here to handle
        // .... when the image has been saved in the photo album
    }
}

And when you call UIImageWriteToSavedPhotosAlbumyou will use it like this:

当你打电话时，UIImageWriteToSavedPhotosAlbum你会像这样使用它：

UIImageWriteToSavedPhotosAlbum(theImage,
   self, // send the message to 'self' when calling the callback
   @selector(thisImage:hasBeenSavedInPhotoAlbumWithError:usingContextInfo:), // the selector to tell the method to call on completion
   NULL); // you generally won't need a contextInfo here

Notethe multiple ':' in the @selector(...)syntax. The colons are part of the method name so don't forget to add these ':' in the @selector(event the trainling one) when you write this line!

注意@selector(...)语法中的多个“:” 。冒号是方法名称的一部分，所以在写这一行时不要忘记在@selector（事件训练）中添加这些':'！

回答by matt

Calling UIImageWriteToSavedPhotosAlbum in modern iOS and Swift

在现代 iOS 和 Swift 中调用 UIImageWriteToSavedPhotosAlbum

In modern iOS, there is an additional requirement for using UIImageWriteToSavedPhotosAlbum. You have to include in your Info.plista key NSPhotoLibraryAddUsageDescription("Privacy - Photo Library Additions Usage Description"). This is so that the system can present the user with a dialog requesting permission to write into the camera roll.

在现代 iOS 中，使用 UIImageWriteToSavedPhotosAlbum 有一个额外的要求。您必须在Info.plist 中包含一个键NSPhotoLibraryAddUsageDescription（“隐私 - 照片库添加使用说明”）。这样系统就可以向用户显示一个对话框，请求允许写入相机胶卷。

You can then call UIImageWriteToSavedPhotosAlbum in your code:

然后，您可以在代码中调用 UIImageWriteToSavedPhotosAlbum：

func myFunc() {
    let im = UIImage(named:"smiley.jpg")!
    UIImageWriteToSavedPhotosAlbum(im, self, #selector(savedImage), nil)
}

The last parameter, the context, will usually be nil.

最后一个参数，即上下文，通常是nil.

The idea of the second two parameters, selfand #selector(savedImage), is that your savedImagemethod in selfwill be called back after the image is saved (or not saved). That method should look something like this:

后两个参数selfand的想法#selector(savedImage)是你的savedImage方法 inself会在保存（或不保存）图像后回调。该方法应如下所示：

@objc func savedImage(_ im:UIImage, error:Error?, context:UnsafeMutableRawPointer?) {
    if let err = error {
        print(err)
        return
    }
    print("success")
}

A typical error would be if the user refused permission in the system dialog. If all goes well, the error will be niland you'll know that the write succeeded.

一个典型的错误是如果用户拒绝了系统对话框中的权限。如果一切顺利，就会出现错误nil，您就会知道写入成功。

In general, UIImageWriteToSavedPhotosAlbum should probably be avoided, in favor of the Photos framework. However, it's a simple way to get the job done.

一般来说，应该避免使用 UIImageWriteToSavedPhotosAlbum，而使用照片框架。但是，这是完成工作的简单方法。

回答by Douglas Pfeifer

SWIFT VERSION based on AliSoftware solution

基于 AliSoftware 解决方案的 SWIFT VERSION

UIImageWriteToSavedPhotosAlbum(
    yourImage,
    self, // send the message to 'self' when calling the callback
    #selector(image(path:didFinishSavingWithError:contextInfo:)), // the selector to tell the method to call on completion
    nil // you generally won't need a contextInfo here
)

@objc private func image(path: String, didFinishSavingWithError error: NSError?, contextInfo: UnsafeMutableRawPointer?) {
    if ((error) != nil) {
        // Do anything needed to handle the error or display it to the user
    } else {
        // .... do anything you want here to handle
        // .... when the image has been saved in the photo album
    }
}