context demo works

step2-04/demo/src/TodoContext.ts

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+import React from 'react';
+
+// The typing forces us to put something inside createContext(); start with undefined
+export const TodoContext = React.createContext(undefined);

step2-04/demo/src/components/TodoApp.tsx

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+import React from 'react';
+import { Stack } from 'office-ui-fabric-react';
+import { TodoFooter } from './TodoFooter';
+import { TodoHeader } from './TodoHeader';
+import { TodoList } from './TodoList';
+import { Store } from '../store';
+import { TodoContext } from '../TodoContext';
+
+let index = 0;
+
+export class TodoApp extends React.Component<any, Store> {
+  constructor(props) {
+    super(props);
+    this.state = {
+      todos: {},
+      filter: 'all'
+    };
+  }
+  render() {
+    return (
+      <TodoContext.Provider
+        value={{
+          ...this.state,
+          addTodo: this._addTodo,
+          remove: this._remove,
+          complete: this._complete,
+          clear: this._clear,
+          setFilter: this._setFilter,
+          edit: this._edit
+        }}
+      >
+        <Stack horizontalAlign="center">
+          <Stack style={{ width: 400 }} gap={25}>
+            <TodoHeader />
+            <TodoList />
+            <TodoFooter />
+          </Stack>
+        </Stack>
+      </TodoContext.Provider>
+    );
+  }
+
+  private _addTodo = label => {
+    const { todos } = this.state;
+    const id = index++;
+
+    this.setState({
+      todos: { ...todos, [id]: { label } }
+    });
+  };
+
+  private _remove = id => {
+    const newTodos = { ...this.state.todos };
+    delete newTodos[id];
+
+    this.setState({
+      todos: newTodos
+    });
+  };
+
+  private _complete = id => {
+    const newTodos = { ...this.state.todos };
+    newTodos[id].completed = !newTodos[id].completed;
+
+    this.setState({
+      todos: newTodos
+    });
+  };
+
+  private _edit = (id, label) => {
+    const newTodos = { ...this.state.todos };
+    newTodos[id] = { ...newTodos[id], label };
+
+    this.setState({
+      todos: newTodos
+    });
+  };
+
+  private _clear = () => {
+    const { todos } = this.state;
+    const newTodos = {};
+
+    Object.keys(this.state.todos).forEach(id => {
+      if (!todos[id].completed) {
+        newTodos[id] = todos[id];
+      }
+    });
+
+    this.setState({
+      todos: newTodos
+    });
+  };
+
+  private _setFilter = filter => {
+    this.setState({
+      filter: filter
+    });
+  };
+}

step2-04/demo/src/components/TodoFooter.tsx

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+import React, { useContext } from 'react';
+import { DefaultButton, Stack, Text } from 'office-ui-fabric-react';
+import { TodoContext } from '../TodoContext';
+
+export const TodoFooter = () => {
+  const context = useContext(TodoContext);
+  const itemCount = Object.keys(context.todos).filter(id => !context.todos[id].completed).length;
+
+  return (
+    <Stack horizontal horizontalAlign="space-between">
+      <Text>
+        {itemCount} item{itemCount === 1 ? '' : 's'} left
+      </Text>
+      <DefaultButton onClick={() => context.clear()}>Clear Completed</DefaultButton>
+    </Stack>
+  );
+};

step2-04/demo/src/components/TodoHeader.tsx

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+import React from 'react';
+import { Stack, Text, Pivot, PivotItem, TextField, PrimaryButton } from 'office-ui-fabric-react';
+import { FilterTypes } from '../store';
+import { TodoContext } from '../TodoContext';
+
+interface TodoHeaderState {
+  labelInput: string;
+}
+
+export class TodoHeader extends React.Component<{}, TodoHeaderState> {
+  constructor(props: {}) {
+    super(props);
+    this.state = { labelInput: undefined };
+  }
+
+  render() {
+    return (
+      <Stack gap={10}>
+        <Stack horizontal horizontalAlign="center">
+          <Text variant="xxLarge">todos</Text>
+        </Stack>
+
+        <Stack horizontal gap={10}>
+          <Stack.Item grow>
+            <TextField
+              placeholder="What needs to be done?"
+              value={this.state.labelInput}
+              onChange={this.onChange}
+              styles={props => ({
+                ...(props.focused && {
+                  field: {
+                    backgroundColor: '#c7e0f4'
+                  }
+                })
+              })}
+            />
+          </Stack.Item>
+          <PrimaryButton onClick={this.onAdd}>Add</PrimaryButton>
+        </Stack>
+
+        <Pivot onLinkClick={this.onFilter}>
+          <PivotItem headerText="all" />
+          <PivotItem headerText="active" />
+          <PivotItem headerText="completed" />
+        </Pivot>
+      </Stack>
+    );
+  }
+
+  private onAdd = () => {
+    this.context.addTodo(this.state.labelInput);
+    this.setState({ labelInput: undefined });
+  };
+
+  private onChange = (evt: React.FormEvent<HTMLInputElement>, newValue: string) => {
+    this.setState({ labelInput: newValue });
+  };
+
+  private onFilter = (item: PivotItem) => {
+    this.context.setFilter(item.props.headerText as FilterTypes);
+  };
+}
+
+TodoHeader.contextType = TodoContext;

step2-04/demo/src/components/TodoList.tsx

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+import React, { useContext } from 'react';
+import { Stack } from 'office-ui-fabric-react';
+import { TodoListItem } from './TodoListItem';
+import { Store, FilterTypes } from '../store';
+import { TodoContext } from '../TodoContext';
+
+export const TodoList = () => {
+  const context = useContext(TodoContext);
+  const { filter, todos } = context;
+  const filteredTodos = Object.keys(todos).filter(id => {
+    return filter === 'all' || (filter === 'completed' && todos[id].completed) || (filter === 'active' && !todos[id].completed);
+  });
+
+  return (
+    <Stack gap={10}>
+      {filteredTodos.map(id => (
+        <TodoListItem key={id} id={id} />
+      ))}
+    </Stack>
+  );
+};

step2-04/demo/src/components/TodoListItem.tsx

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+import React from 'react';
+import { Stack, Checkbox, IconButton, TextField, DefaultButton } from 'office-ui-fabric-react';
+import { TodoContext } from '../TodoContext';
+
+interface TodoListItemProps {
+  id: string;
+}
+
+interface TodoListItemState {
+  editing: boolean;
+  editLabel: string;
+}
+
+export class TodoListItem extends React.Component<TodoListItemProps, TodoListItemState> {
+  constructor(props: TodoListItemProps) {
+    super(props);
+    this.state = { editing: false, editLabel: undefined };
+  }
+
+  render() {
+    const { id } = this.props;
+    const { todos, complete, remove } = this.context;
+
+    const item = todos[id];
+
+    return (
+      <Stack horizontal verticalAlign="center" horizontalAlign="space-between">
+        {!this.state.editing && (
+          <>
+            <Checkbox label={item.label} checked={item.completed} onChange={() => complete(id)} />
+            <div>
+              <IconButton iconProps={{ iconName: 'Edit' }} onClick={this.onEdit} />
+              <IconButton iconProps={{ iconName: 'Cancel' }} onClick={() => remove(id)} />
+            </div>
+          </>
+        )}
+
+        {this.state.editing && (
+          <Stack.Item grow>
+            <Stack horizontal gap={10}>
+              <Stack.Item grow>
+                <TextField value={this.state.editLabel} onChange={this.onChange} />
+              </Stack.Item>
+              <DefaultButton onClick={this.onDoneEdit}>Save</DefaultButton>
+            </Stack>
+          </Stack.Item>
+        )}
+      </Stack>
+    );
+  }
+
+  private onEdit = () => {
+    const { id } = this.props;
+    const { todos } = this.context;
+    const { label } = todos[id];
+
+    this.setState({
+      editing: true,
+      editLabel: this.state.editLabel || label
+    });
+  };
+
+  private onDoneEdit = () => {
+    this.context.edit(this.props.id, this.state.editLabel);
+    this.setState({
+      editing: false,
+      editLabel: undefined
+    });
+  };
+
+  private onChange = (evt: React.FormEvent<HTMLInputElement>, newValue: string) => {
+    this.setState({ editLabel: newValue });
+  };
+}
+
+TodoListItem.contextType = TodoContext;

step2-04/demo/src/index.tsx

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+import React from 'react';
+import ReactDOM from 'react-dom';
+import { TodoApp } from './components/TodoApp';
+import { initializeIcons } from '@uifabric/icons';
+
+// Initializes the UI Fabric icons that we can use
+// Choose one from this list: https://developer.microsoft.com/en-us/fabric#/styles/icons
+initializeIcons();
+
+ReactDOM.render(<TodoApp />, document.getElementById('app'));

step2-04/demo/src/store/index.ts

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+export type FilterTypes = 'all' | 'active' | 'completed';
+
+export interface TodoItem {
+  label: string;
+  completed: boolean;
+}
+
+export interface Store {
+  todos: {
+    [id: string]: TodoItem;
+  };
+
+  filter: FilterTypes;
+}