如何从Observable中止Ajax请求？ [英] How to abort an Ajax request from an Observable?

问题描述

我的代码包含我用来将文件上传到我的PHP服务器的简单函数（嵌套在 RxJS / Observable中的 xhr 请求）：

My code contains this simple function I'm using to upload files to my PHP server (there's an xhr request nested in an RxJS/Observable):

fileUpload(file: File): Observable<any> {
    return new Observable( observer => {
        let xhr:XMLHttpRequest = new XMLHttpRequest();
        xhr.onreadystatechange = () => {
            if (xhr.readyState === 4) {
                if (xhr.status === 200) {
                    observer.next(<any>JSON.parse(xhr.response));
                } else {
                    observer.error(xhr.response);
                    observer.complete();
                }
            }
        };

        xhr.open('POST', '__BACKEND__?action=file-upload', true);
        var formData = new FormData();
        formData.append('file', file, file.name);
        xhr.send(formData);
    });
}

它完全正常运行但现在我还想添加一些取消机械师。

It is completely functional but now I would also like to add some sort of a cancellation mechanic to it.

只是取消订阅Observable是行不通的，因为我需要以某种方式调用 xhr.abort（）或我通过大量上传浪费了宝贵的资源。

Just unsubscribing from the Observable won't work, because I need to somehow call xhr.abort() or I waste precious resources with large uploads.

是否可以通过修改此代码来获得优雅的解决方案，或者我做错了因为我使用了 RxJS / Observable 执行此任务？

Is it possible to get an elegant solution by modifying this code or am I doing it wrong because I'm using an RxJS/Observable for this task?

推荐答案

创建<$ c $时c> Observable 您可以通过返回订阅或函数来指定取消订阅行为构建器函数：

When you create an Observable you can specify the unsubscribe behavior by returning a Subscription or a function from builder function:

fileUpload(file: File): Observable<any> {
    return new Observable( observer => {
        let xhr:XMLHttpRequest = new XMLHttpRequest();
        xhr.onreadystatechange = () => {
            if (xhr.readyState === 4) {
                if (xhr.status === 200) {
                    observer.next(<any>JSON.parse(xhr.response));
                    observer.complete();
                } else {
                    observer.error(xhr.response);
                }
            }
        };

        xhr.open('POST', '__BACKEND__?action=file-upload', true);
        var formData = new FormData();
        formData.append('file', file, file.name);
        xhr.send(formData);

        //Return the tear down logic. 
        //You may also want to check here that it has not already completed
        //Since this gets called in all cases when the `Subscription` terminates
        return () => xhr.abort();
    });
}

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