当Observables用于涉及大量链接和大量异步操作的某些任务时，例如列出文件夹中的所有项目并检查其中的所有文件夹以查找特定文件，我经常最终需要为每个任务（return Observable.of(folder)...）构建复杂的链，或者将某些特殊值转发到最后以表示批处理结束（每个操作符以if(res === false) return Observable.of(false)开头）。
有点像你在杂货店和结账时面前的人之间放的那根棍子。
似乎应该有一种更好的方法，不涉及通过各种回调和运算符转发停止值。
那么调用一个带有文件夹路径字符串的函数并返回其中所有文件和文件夹的列表的好方法是什么。它还指定文件是否为HTML文件，以及文件夹是否包含名为tiddlywiki.json的文件。
唯一的要求是它不能返回Observable.of(...)...之类的内容。它可能应该在链的顶部有一个主题，但这不是一个要求。
function listFolders(folder) {
return [
{ type: 'folder', name: 'folder1' },
{ type: 'datafolder', name: 'folder2' }, //contains "tiddlywiki.json" file
{ type: 'folder', name: 'folder3' },
{ type: 'htmlfile', name: 'test.html' },
{ type: 'other', name: 'mytest.txt' }
]
}
答案 0 :(得分：0)
这是一个不遵循我规定的规则（见下面的规则），但是花了大约十分钟，使用第一个作为指导。
export function statFolder(subscriber, input: Observable<any>) {
return input.mergeMap(([folder, tag]) => {
return obs_readdir({ folder, tag })(folder);
}).mergeMap(([err, files, { folder, tag }]) => {
if (err) { return Observable.of({ error: err }) as any; }
else return Observable.from(files).mergeMap(file => {
return obs_stat([file,folder])(path.join(folder, file as string));
}).map(statFolderEntryCB).mergeMap<any, any>((res) => {
let [entry, [name, folder]] = res as [any, [string, string, number, any]];
if (entry.type === 'folder')
return obs_readdir([entry])(path.join(entry.folder, entry.name));
else return Observable.of([true, entry]);
}, 20).map((res) => {
if (res[0] === true) return (res);
let [err, files, [entry]] = res as [any, string[], [FolderEntry, number, any]];
if (err) {
entry.type = "error";
} else if (files.indexOf('tiddlywiki.json') > -1)
entry.type = 'datafolder';
return ([true, entry]);
}).reduce((n, [dud, entry]) => {
n.push(entry);
return n;
}, []).map(entries => {
return { entries, folder, tag };
}) as Observable<{ entries: any, folder: any, tag: any }>;
}).subscribe(subscriber);
}
原文：这需要花费几个小时来编写......它可以正常工作......但是...它使用了concatMap，因此它一次只能接受一个请求。它使用我为此目的编写的自定义运算符。
export function statFileBatch(subscriber, input: Observable<any>) {
const signal = new Subject<number>();
var count = 0;
//use set timeout to fire after the buffer recieves this item
const sendSignal = (item) => setTimeout(() => { count = 0; signal.next(item); });
return input.concatMap(([folder, tag]) => {
return obs_readdir({ folder, tag })(folder);
}).lift({
call: (subs: Subscriber<any>, source: Observable<any>) => {
const signalFunction = (count) => signal.mapTo(1), forwardWhenEmpty = true;
const waiting = [];
const _output = new Subject();
var _count = new Subject<number>()
const countFactory = Observable.defer(() => {
return Observable.create(subscriber => {
_count.subscribe(subscriber);
})
});
var isEmpty = true;
const sourceSubs = source.subscribe(item => {
if (isEmpty && forwardWhenEmpty) {
_output.next(item);
} else {
waiting.push(item)
}
isEmpty = false;
})
const pulse = new Subject<any>();
const signalSubs = pulse.switchMap(() => {
return signalFunction(countFactory)
}).subscribe(count => {
//act on the closing observable value
var i = 0;
while (waiting.length > 0 && i++ < count)
_output.next(waiting.shift());
//if nothing was output, then we are empty
//if something was output then we are not
//this is meant to be used with bufferWhen
if (i === 0) isEmpty = true;
_count.next(i);
_count.complete();
_count = new Subject<number>();
pulse.next();
})
pulse.next(); //prime the pump
const outputSubs = Observable.create((subscriber) => {
return _output.subscribe(subscriber);
}).subscribe(subs) as Subscription;
return function () {
outputSubs.unsubscribe();
signalSubs.unsubscribe();
sourceSubs.unsubscribe();
}
}
}).mergeMap(([err, files, { folder, tag }]) => {
if (err) { sendSignal(err); return Observable.empty(); }
return Observable.from(files.map(a => [a, folder, files.length, tag])) as any;
}).mergeMap((res: any) => {
let [file, folder, fileCount, tag] = res as [string, string, number, any];
return obs_stat([file, folder, fileCount, tag])(path.join(folder, file))
}, 20).map(statFolderEntryCB).mergeMap<any, any>((res) => {
let [entry, [name, folder, fileCount, tag]] = res as [any, [string, string, number, any]];
if (entry.type === 'folder')
return obs_readdir([entry, fileCount, tag])(path.join(entry.folder, entry.name));
else return Observable.of([true, entry, fileCount, tag]);
}, 20).map((res) => {
//if (res === false) return (false);
if (res[0] === true) return (res);
let [err, files, [entry, fileCount, tag]] = res as [any, string[], [FolderEntry, number, any]];
if (err) {
entry.type = "error";
} else if (files.indexOf('tiddlywiki.json') > -1)
entry.type = 'datafolder';
return ([true, entry, fileCount, tag]);
}).map(([dud, entry, fileCount, tag]) => {
count++;
if (count === fileCount) {
sendSignal([count, tag]);
}
return entry;
}).bufferWhen(() => signal).withLatestFrom(signal).map(([files, [sigResult, tag]]: any) => {
return [
typeof sigResult !== 'number' ? sigResult : null, //error object
files, //file list
typeof sigResult === 'number' ? sigResult : null, //file count
tag //tag
];
}).subscribe(subscriber);
}