adding step 2.4 and 2.5 exercises

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

@@ -0,0 +1,64 @@
+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;