创建底部导航时反应本机错误

Question

我正在尝试在React本机项目中创建底部导航。我收到此错误

不变违规：元素类型无效：预期的字符串（对于内置组件）或类/函数（对于复合组件），但未定义。您可能忘记了从定义文件中导出组件，或者可能混淆了默认导入和命名导入

但是我确实导出了所有文件，并且没有混入任何默认导入或命名导入。

Index.js

import React from 'react';
import { AppRegistry } from 'react-native';
import App from './App';
import { name as appName } from './app.json';
import { createStore } from 'redux';
import { Provider } from 'react-redux';
import rootReducer from './src/redux/reducers/rootReducer'
import { NavigationContainer } from '@react-navigation/native'

const store = createStore(rootReducer)

const Root = () => (
    <Provider store={store}>
        <NavigationContainer>
            <App />
        </NavigationContainer>
    </Provider>
)

AppRegistry.registerComponent(appName, () => Root);

App.js

import React from 'react';
import { createMaterialBottomTabNavigator } from '@react-navigation/material-bottom-tabs';
import { MaterialCommunityIcons } from 'react-native-vector-icons';

import Accounts from './src/components/Accounts';
import Categories from './src/components/Categories';
import Transactions from './src/components/Transactions';
import Budget from './src/components/Budget';
import Overview from './src/components/Overview';

const Tab = createMaterialBottomTabNavigator();

export default App = () => {
  return (
    <Tab.Navigator
      initialRouteName="Accounts"
      activeColor="#e91e63"
      labelStyle={{ fontSize: 12 }}
      style={{ backgroundColor: 'tomato' }}
    >
      <Tab.Screen
        name="Accounts"
        component={Accounts}
        options={{
          tabBarLabel: 'Home',
          tabBarIcon: ({ color, size }) => (
            <MaterialCommunityIcons name="home" color={color} size={size} />
          ),
        }}
      />
      <Tab.Screen ... />
<Tab.Screen ... />
    </Tab.Navigator>
  );
}

我的编码有什么错误？我已经经历了先前的问题，但是所有解决方案都将默认值更改为named，反之亦然。

Answer 1

添加导出默认值解决了我的问题

import matplotlib.pyplot as plt
import cartopy.crs as ccrs
#import cartopy.feature as cfeature
import numpy as np

# make up data for plotting
xmin, xmax, ymin, ymax = -55, 15, -4, 4
#extent = [xmin, xmax, ymin, ymax]
width = 4
height = 4
xs = np.linspace(xmin, xmax, width)
ys = np.linspace(ymin, ymax, height)
x2d, y2d = np.meshgrid(xs, ys)
z2d = (x2d+y2d)

fig = plt.figure(figsize=(20,5))  # set figsize (width, height) here
ax = plt.axes(projection=ccrs.PlateCarree())

ct = ax.contourf(x2d, y2d, z2d, 30, cmap='RdBu_r')

ax.coastlines()
gridlines = ax.gridlines(draw_labels=True)

# create a colorbar
cbar = plt.colorbar(ct, fraction=.08, pad=0.04, shrink=0.5, aspect=12)
cbar.set_label('Power Spectrum (m$^2$/# frequencies)', labelpad=15, y=.5, rotation=270)

plt.title('Frequency Summed Power Spectrum (2018-2019)', y=1.2)
plt.show()