Question

我的项目是Cordova + React（es6）。我在使用setState（）时遇到了一些问题。

传递给state的数据不为空。但是，将数据传递给状态，我收到结果状态为空。

我的项目的env（package.json）：

    #include <string>
    #include <iostream>
    using namespace std;

int main() {

string str;
long szam = 0, Dec, num, Base = 1, x,i=1;
cout << "the number : ";
cin >> str;
cout << "The input number system:";
cin >> x;

   while (str[i] == '\0')
     {
       if (str[i] = 'A') { num = 10;}
       else if (str[i] = 'B') { num = 11; }
       else if (str[i] = 'C') { num = 12; }
       else if (str[i] = 'D') { num = 13; }
       else if (str[i] = 'E') { num = 14; }
       else if (str[i] = 'F') { num = 15; }
       else { num = str[i] - '0'; }

       Dec = Dec + num * Base;
       Base = Base * x;

      }
cout << szam << endl;
return 0;

我的代码：

{
  "name": "MYAPP",
  "version": "1.0.0",
  "description": "this is front of simula's app",
  "main": "gulpfile.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "build": "browserify ./www/jsx/app.jsx -t babelify -o ./www/js/app.js"
  },
  "author": "maki",
  "license": "ISC",
  "dependencies": {
    "babel-preset-es2015": "^6.13.2",
    "browserify": "^13.1.0",
    "gulp": "^3.9.1",
    "history": "^4.2.0",
    "material-design-icons": "^2.2.3",
    "material-ui": "^0.15.4",
    "rd3": "^0.7.2",
    "react": "^15.3.0",
    "react-d3": "^0.4.0",
    "react-dom": "^15.3.1",
    "react-motion": "^0.4.4",
    "react-router": "^2.7.0",
    "react-swipeable-views": "^0.7.0",
    "react-tap-event-plugin": "^1.0.0",
    "vinyl-source-stream": "^1.1.0"
  },
  "devDependencies": {
    "babel-cli": "^6.11.4",
    "babel-plugin-transform-class-properties": "^6.11.5",
    "babel-preset-react": "^6.11.1",
    "babel-preset-stage-1": "^6.13.0",
    "babelify": "^7.3.0",
    "gulp-sass": "^2.3.2",
    "jquery": "^3.1.0"
  }
}

我该怎么做???

Answer 1

React setState()是一个异步操作，因此在您的代码中调用后不会立即传递结果。如果在您的render（）方法中添加console.log(this.state.data_source); ，则可以访问更新后的状态，该方法仅在this.setState()完成时调用。

请使用React文档：https://facebook.github.io/react/docs/component-api.html#setstate


setState（）不会立即改变this.state，但会创建挂起状态转换。调用此方法后访问this.state可能会返回现有值。   无法保证对setState的调用同步操作，并且可以对调用进行批处理以获得性能提升。

setState（）将始终触发重新渲染，除非在shouldComponentUpdate（）中实现条件渲染逻辑。

Answer 2

除了Piotr'a答案之外，setState可以传递一个用新状态调用的回调，例如;

  this.setState({data_source: final_cash_data}, function(newState){
    console.log(newState.data_source)
  });

React：setState没有按预期生成结果（不工作？）

2 个答案: