DART somo la 43: Stream kwenye Dart

Stream ni mfululizo wa asynchronous operations (events) yaani matukio ya asyncchronous ambayo huwasilisha malue nyingi ambazo hupatikanwa katika wakati ujao. Utafauti mkubwa wa future ni kuwa kwenye future class tunasumngumza operation moja kama tulivyoona huko nyuma, lakini ukija kwenye stream unazungumzia operationa zaidi ya moja ni sawa na iliteration kwenye synchronous operation.

Jinsi ya kutengeneza stream class

Kutengeneza stream class kuna mfanano sawa na future. Utaanza na keyword stream ikifuatiwa na aina ya data kama tulivyoona kwenye stream ikifuatiwa na function, ikifutaiwa na keyword async itafuatiwa na body of function. Sasa kwenye async utaongeza alama ya nyita (*).

Stream<String> tovuti() async* {

 await Future.delayed(Duration(seconds: 1));

 yield 'bongoclass';

 await Future.delayed(Duration(seconds: 1));

 yield 'facebook';

 await Future.delayed(Duration(seconds: 1));

 yield 'Google';

}

// main function

void main() async {

 // you can use await for loop to get the value from stream

 await for (String jina in tovuti()) {

   print(jina);

 }

}

Pia tunaweza kutumia keyword yield ili kuweza kufanya iliteration. Angalia mfano hapo chini:

Stream<int> countForOneMinute() async* {

 for (int i = 1; i <= 5; i++) {

   await Future.delayed(const Duration(seconds: 1));

   yield i;

 }

} main() async {

 await for (int i in countForOneMinute()) {

   print(i);

 }

}

Pia tunaweza kutumia yield* kwenye stream ama recrucive function, rejea kwenye somo a function kujuwa maana ya recrucive function

Stream<int> str(int n) async* {

 if (n > 0) {

   await Future.delayed(Duration(seconds: 2));

   yield n;

   yield* str(n - 2);

 }

}

void main() {

 str(10).f...