dart - Flutter:如何一次又一次停止不必要地渲染 "Widget build()"？

Question

这是 Flutter 中的一个小型 POC，其中我的 build() 函数被一次又一次地调用。

如果没有任何循环，这完全出乎意料，经过大量研究，我也在 initState() 中调用 “Future”。

但是仍然面临着同样的问题。

预先感谢您的宝贵时间!

What have I tried..

import 'package:flutter/material.dart';

//http_request
import 'package:http/http.dart' as http; //to handle the http request
// import 'dart:async'; // for async functions
import 'dart:async' show Future;
import 'dart:convert'; //to convert the http response in JSON formate

import 'HomePage.dart';

    class Reports extends StatefulWidget {
      @override
      _Reports createState() => _Reports();
    }

    class _Reports extends State<Reports> {
  static String url = "Some Url";
  String _response = "abc";
  @override
  void initState() {
    super.initState();
    getTradeName_dropdown_ITR_Computation_DATA();
  }

  @override
  Widget build(BuildContext context) {

    print('body');

    return Scaffold(
      body: Container(
        child: new Text(_response),
      ),
    );
  }

  Future getTradeName_dropdown_ITR_Computation_DATA() async {
    try {
      http.Response response =
              await http.get("http://" + url );
      if (this.mounted) {
        setState(() {

          String jsonTradeName_dropdown = response.body;
          _response = jsonTradeName_dropdown;
        });
      }
    } on Exception {
      setState(() {
        _response = "Some error occored. Please Try again...";
      });
    }
  }
}

output:

I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body

Answer 1

你犯了几个错误，这是正确的代码。您应该使用 String 而不是 Text 小部件来显示响应。

class _Reports extends State<Reports> {
  static String url = "url";
  String _response = "abc";
  @override
  void initState() {
    super.initState();
    getTradeName_dropdown_ITR_Computation_DATA();
  }

  @override
  Widget build(BuildContext context) {

    print('body');

    return Scaffold(
      body: Container(
        child: new Text(_response),
      ),
    );
  }

  Future getTradeName_dropdown_ITR_Computation_DATA() async {
    try {
      http.Response response =
      await http.get("url_goes_here");

      if (this.mounted) {
        setState(() {
          String jsonTradeName_dropdown = response.body;
          _response = jsonTradeName_dropdown;
        });
      }
    } on Exception {
      setState(() {
        _response = "Some error occored. Please Try again...";
      });
    }
  }
}