How to update context with hooks is discussed in the How to avoid passing callbacks down? part of the Hooks FAQ.
The argument passed to createContext
will only be the default value if the component that uses useContext
has no Provider
above it further up the tree. You could instead create a Provider
that supplies the style
and visibility
as well as functions to toggle them.
Example
const { createContext, useContext, useState } = React;
const ThemeContext = createContext(null);
function Content() {
const { style, visible, toggleStyle, toggleVisible } = useContext(
ThemeContext
);
return (
<div>
<p>
The theme is <em>{style}</em> and state of visibility is
<em> {visible.toString()}</em>
</p>
<button onClick={toggleStyle}>Change Theme</button>
<button onClick={toggleVisible}>Change Visibility</button>
</div>
);
}
function App() {
const [style, setStyle] = useState("light");
const [visible, setVisible] = useState(true);
function toggleStyle() {
setStyle(style => (style === "light" ? "dark" : "light"));
}
function toggleVisible() {
setVisible(visible => !visible);
}
return (
<ThemeContext.Provider
value={{ style, visible, toggleStyle, toggleVisible }}
>
<Content />
</ThemeContext.Provider>
);
}
ReactDOM.render(<App />, document.getElementById("root"));
<script src="https://unpkg.com/react@16/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@16/umd/react-dom.development.js"></script>
<div id="root"></div>