如何使用Dart ChangeNotifier类？ [英] How to use Dart ChangeNotifier class?

问题描述

我在Dart的observe库中探索ChangeNotifier类，以便在命令行应用程序中使用。但是，我有两个问题。

1. List< ChangeRecord> ; 对象在每次更新记录时递增重复。查看图片：

   
   
   

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2. ChangeRecord不允许仅检索新值。因此，我试图使用MapChangeRecord代替。

这是我的示例代码供参考：

  import'dart：io' 
 import'dart：async'; 
 import'dart：convert'; 
 import'package：observe / observe.dart'; 
 
类Notifiable extends Object with ChangeNotifier {
 String _input =''; 
 @reflectable get input => _input; 
 @reflectable set input（val）{
 _input = notifyPropertyChange（#input，_input，val）; 
} 
 
 void change（String text）{
 input = text; 
 this.changes.listen（（List< ChangeRecord> record）=> print（record.last））; 
} 
} 
 
 void main（）{
 Notifiable notifiable = new Notifiable（）; 
 Stream stdinStream = stdin; 
 stdinStream 
 .transform（new Utf8Decoder（））
 .listen（（e）=> notifiable.change（e））;每次执行此代码时，
} 
  

解决方案

  stdinStream 
 .transform（new Utf8Decoder（））
。 （（e）=> notifiable.change（e））; 
  

您在 notifiable.change（e）

如果您更改为

  import'dart：io'; 
 import'dart：async'; 
 import'dart：convert'; 
 import'package：observe / observe.dart'; 
 
类Notifiable extends Object with ChangeNotifier {
 String _input =''; 
 @reflectable get input => _input; 
 @reflectable set input（val）{
 _input = notifyPropertyChange（#input，_input，val）; 
} 
 
 Notifiable（）{
 this.changes.listen（（List< ChangeRecord> record）=> print（record.last））; 
} 
 
 void change（String text）{
 input = text; 
} 
} 
 
 void main（）{
 Notifiable notifiable = new Notifiable（）; 
 Stream stdinStream = stdin; 
 stdinStream 
 .transform（new Utf8Decoder（））
 .listen（（e）=> notifiable.change（e））; 
} 
  

它应该能正常工作

I'm exploring the ChangeNotifier class in Dart's observe library for use in a commandline application. But, I'm having two issues.

1. The number of reported changes in a List<ChangeRecord> object are incrementally repeated in each update to the record. See image:

2. ChangeRecord doesn't allow for retrieving only new values. Thus, I'm trying to use a MapChangeRecord instead. But, I don't know how to use it.

This is my sample code for reference:

import 'dart:io';
import 'dart:async';
import 'dart:convert';
import 'package:observe/observe.dart';

class Notifiable extends Object with ChangeNotifier {
  String _input = ''; 
  @reflectable get input => _input;
  @reflectable set input(val) {
    _input = notifyPropertyChange(#input, _input, val);
  }

  void change(String text) {
    input = text;
    this.changes.listen((List<ChangeRecord> record) => print(record.last));
  }
}

void main() {
  Notifiable notifiable = new Notifiable();
  Stream stdinStream = stdin;
  stdinStream
    .transform(new Utf8Decoder())
      .listen((e) => notifiable.change(e));
}

解决方案

each time this code is executed

stdinStream
    .transform(new Utf8Decoder())
      .listen((e) => notifiable.change(e));

you add a new subscription in notifiable.change(e)

If you change it like

import 'dart:io';
import 'dart:async';
import 'dart:convert';
import 'package:observe/observe.dart';

class Notifiable extends Object with ChangeNotifier {
  String _input = '';
  @reflectable get input => _input;
  @reflectable set input(val) {
    _input = notifyPropertyChange(#input, _input, val);
  }

  Notifiable() {
    this.changes.listen((List<ChangeRecord> record) => print(record.last));
  }

  void change(String text) {
    input = text;
  }
}

void main() {
  Notifiable notifiable = new Notifiable();
  Stream stdinStream = stdin;
  stdinStream
    .transform(new Utf8Decoder())
      .listen((e) => notifiable.change(e));
}

it should work as expected

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