Skip to content

UI - Main screen

Because we want the Main screen to be rendered behind the editing popup, we will draw it first, and then have additional logic about our popups

Our layout

Now that we have our Frame, we can actually begin drawing widgets onto it. We will begin by creating our layout.

let chunks = Layout::default()

The variable chunks now contains a length 3 array of Rect objects that contain the top left corner of their space, and their size. We will use these later, after we prepare our widgets.

The title

The title is an important piece for any application. It helps the user understand what they can do and where they are. To create our title, we are going to use a Paragraph widget (which is used to display only text), and we are going to tell that Paragraph we want a border all around it by giving it a Block with borders enabled. See Block recipes and Paragraph recipes for more information about Block and Paragraph.

let title_block = Block::default()
let title = Paragraph::new(Text::styled(
"Create New Json",
f.render_widget(title, chunks[0]);

In this code, the first thing we do, is create a Block with all borders enabled, and the default style. Next, we created a paragraph widget with the text “Create New Json” styled green. See Paragraph recipes for more information about creating paragraphs and Styling text recipes for styling text. Finally, we call render_widget on our Frame, and give it the widget we want to render it, and the Rect representing where it needs to go and what size it should be. (this is the way all widgets are drawn)

The list of existing pairs

We would also like the user to be able to see any key-value pairs that they have already entered. For this, we will be using another widget, the List. The list is what it sounds like - it creates a new line of text for each ListItem, and it supports passing in a state so you can implement selecting items on the list with little extra work. We will not be implementing selection, as we simply want the user to be able to see what they have already entered.

let mut list_items = Vec::<ListItem>::new();
for key in app.pairs.keys() {
format!("{: <25} : {}", key, app.pairs.get(key).unwrap()),
let list = List::new(list_items);
f.render_widget(list, chunks[1]);

For more information on Line, Span, and Style see Displaying Text recipes

In this piece of the function, we create a vector of ListItems, and populate it with styled and formatted key-value pairs. Finally, we create the List widget, and render it.

The bottom navigational bar

It can help new users of your application to see hints about what keys they can press. For this, we are going to implement two bars, and another layout. These two bars will contain information on 1) the current screen (Main, Editing, and Exiting), and 2) what keybinds are available.

Here, we will create a Vec of Span which will be converted later into a single line by the Paragraph. (A Span is different from a Line, because a Span indicates a section of Text with a style applied, and doesn’t end with a newline)

let current_navigation_text = vec![
// The first half of the text
match app.current_screen {
CurrentScreen::Main => Span::styled("Normal Mode", Style::default().fg(Color::Green)),
CurrentScreen::Editing => {
Span::styled("Editing Mode", Style::default().fg(Color::Yellow))
CurrentScreen::Exiting => Span::styled("Exiting", Style::default().fg(Color::LightRed)),
// A white divider bar to separate the two sections
Span::styled(" | ", Style::default().fg(Color::White)),
// The final section of the text, with hints on what the user is editing
if let Some(editing) = &app.currently_editing {
match editing {
CurrentlyEditing::Key => {
Span::styled("Editing Json Key", Style::default().fg(Color::Green))
CurrentlyEditing::Value => {
Span::styled("Editing Json Value", Style::default().fg(Color::LightGreen))
} else {
Span::styled("Not Editing Anything", Style::default().fg(Color::DarkGray))
let mode_footer = Paragraph::new(Line::from(current_navigation_text))

Next, we are also going to make a hint in the navigation bar with available keys. This one does not have several sections of text with different styles, and is thus less code.

let current_keys_hint = {
match app.current_screen {
CurrentScreen::Main => Span::styled(
"(q) to quit / (e) to make new pair",
CurrentScreen::Editing => Span::styled(
"(ESC) to cancel/(Tab) to switch boxes/enter to complete",
CurrentScreen::Exiting => Span::styled(
"(q) to quit / (e) to make new pair",
let key_notes_footer =

Finally, we are going to create our first nested layout. Because the Layout.split function requires a Rect, and not a Frame, we can pass one of our chunks from the previous layout as the space for the new layout. If you remember the bottom most section from the above graphic:

This always section should be 3 lines tall Constraint::Length 3

We will create a new layout in this space by passing it (chunks[2]) as the parameter for split.

let footer_chunks = Layout::default()
.constraints([Constraint::Percentage(50), Constraint::Percentage(50)])

The visual equivalent of this code is:

Length 50% Length 50% Constraint::Length 3

And now we can render our footer paragraphs in the appropriate spaces.

f.render_widget(mode_footer, footer_chunks[0]);
f.render_widget(key_notes_footer, footer_chunks[1]);