cursive/doc/tutorial_3.md

Starting with cursive (3/3)

Target goal

In this part, we'll introduce some mutability. Until now, we were adding elements to the UI, and then we'd forget about them. This time, we'll remember them to update them.

Here is the code we'll end up with:

use cursive::Cursive;
use cursive::views::{Button, Dialog, DummyView, EditView,
                     LinearLayout, SelectView};
use cursive::traits::*;

fn main() {
    let mut siv = cursive::default();

    let select = SelectView::<String>::new()
        .on_submit(on_submit)
        .with_name("select")
        .fixed_size((10, 5));
    let buttons = LinearLayout::vertical()
        .child(Button::new("Add new", add_name))
        .child(Button::new("Delete", delete_name))
        .child(DummyView)
        .child(Button::new("Quit", Cursive::quit));

    siv.add_layer(Dialog::around(LinearLayout::horizontal()
            .child(select)
            .child(DummyView)
            .child(buttons))
        .title("Select a profile"));

    siv.run();
}

fn add_name(s: &mut Cursive) {
    fn ok(s: &mut Cursive, name: &str) {
        s.call_on_name("select", |view: &mut SelectView<String>| {
            view.add_item_str(name)
        });
        s.pop_layer();
    }

    s.add_layer(Dialog::around(EditView::new()
            .on_submit(ok)
            .with_name("name")
            .fixed_width(10))
        .title("Enter a new name")
        .button("Ok", |s| {
            let name =
                s.call_on_name("name", |view: &mut EditView| {
                    view.get_content()
                }).unwrap();
            ok(s, &name);
        })
        .button("Cancel", |s| {
            s.pop_layer();
        }));
}

fn delete_name(s: &mut Cursive) {
    let mut select = s.find_name::<SelectView<String>>("select").unwrap();
    match select.selected_id() {
        None => s.add_layer(Dialog::info("No name to remove")),
        Some(focus) => {
            select.remove_item(focus);
        }
    }
}

fn on_submit(s: &mut Cursive, name: &str) {
    s.pop_layer();
    s.add_layer(Dialog::text(format!("Name: {}\nAwesome: yes", name))
        .title(format!("{}'s info", name))
        .button("Quit", Cursive::quit));
}

SelectView

The main element in our application will be a list of names. For this, we'll use a SelectView. This type is generic on the item stored. We just want to store the names, so let's build a SelectView<String>:

let select = SelectView::<String>::new();

Our list will start empty. If we leave it like that, it will be tiny when the application starts, and will grow when we add names. This is not very professional-looking, so we'll give it a fixed size.

To do that, a ResizedView can wrap any view and give it a fixed size. We could do:

let select = ResizedView::with_fixed_size((10, 5), SelectView::<String>::new());

But there is another shorter way: the Resizable trait is conveniently implemented for any View, and allow to wrap in a ResizedView with a chainable call. Resizable, and a few other useful traits, are conveniently bundled in the traits prelude, ready to be imported:

use cursive::traits::*;

let select = SelectView::<String>::new()
    .fixed_size((10, 5));

We'll also want to add a callback when the user chooses a name. The SelectView::on_submit method takes a callback with a second argument: the selected item. Since we're using String, our callback will have to be Fn(&mut Cursive, &str):

let select = SelectView::<String>::new()
    .on_submit(on_submit)
    .fixed_size((10, 5));

fn on_submit(s: &mut Cursive, name: &str) {
    s.pop_layer();
    s.add_layer(Dialog::text(format!("Name: {}\nAwesome: yes", name))
        .title(format!("{}'s info", name))
        .button("Quit", Cursive::quit));
}

(Be sure to call on_submit on the SelectView, not on the ResizedView returned by fixed_size!)

What we do there should be pretty familiar by now: replace the layer with a simple dialog.

Linear layouts

Our main screen is more complex than in our previous examples: it is made of several views. There is a SelectView on the left, and three Buttons to the right. But our Dialog::around method only takes one view! How will we do this?

The solution is to use a layout view to display multiple children side-by-side. LinearLayout, for instance, can display views in a line. We'll use two of them:

• One, set vertically, will hold the buttons on the right.
• Another one, horizontally, will contain the list and the vertical layout.

Let's start with the column of buttons:

let buttons = LinearLayout::vertical()
    .child(Button::new("Add new", add_name))
    .child(Button::new("Delete", delete_name))
    .child(DummyView)
    .child(Button::new("Quit", Cursive::quit));

fn add_name(s: &mut Cursive) {}
fn delete_name(s: &mut Cursive) {}

Buttons here take a regular callback. We're also adding a DummyView here: this view doesn't do anything, it just occupies some space - we're using it as a cheap spacer.

We can now create the second linear layout inside a Dialog:

siv.add_layer(Dialog::around(LinearLayout::horizontal()
        .child(select)
        .child(DummyView)
        .child(buttons))
    .title("Select a profile"));

We've added a DummyView again to add some space between the list and the buttons. Though with an empty list, it doesn't look like much yet. Let's fill this list with names!

Identifying views

When the user presses the <Add new> button, we want to show a popup where he can enter a new name:

fn add_name(s: &mut Cursive) {
    s.add_layer(Dialog::around(EditView::new()
            .fixed_width(10))
        .title("Enter a new name")
        .button("Ok", |s| {
            // What do we do now?...
        })
        .button("Cancel", |s| {
            s.pop_layer();
        }));
}

We're using EditView here, that we wrap in a fixed width like we did with the SelectView earlier. We have an <Ok> button, but... what do we do there?

We need to fetch the content of the EditView from the callback, but we don't have a reference to it. And if you try to declare a variable for the EditView and use it in the closure, you'll soon be submerged by compiler errors, for good reasons. But there is a way!

The closure has access to the &mut Cursive, which in turn has access to all the views, so in theory, we could ask it to borrow the view, if only we knew how to point to the correct view.

IdView is meant exactly for this: it wraps a view and gives it a name. Later, you can ask the Cursive root for this name and get access to the view. Just what we need!

Like ResizedView, IdView can be used directly with IdView::new, or through the Identifiable trait. Cursive::call_on_name allows you to run a closure on the view.

Here's what it looks like in action:

fn add_name(s: &mut Cursive) {
    s.add_layer(Dialog::around(EditView::new()
            .with_name("name")
            .fixed_width(10))
        .title("Enter a new name")
        .button("Ok", |s| {
            let name = s.call_on_name("name", |view: &mut EditView| {
                view.get_content()
            }).unwrap();
        })
        .button("Cancel", |s|
            s.pop_layer();
        }));
}

We create the EditView with the id "name", and we use "name" again when calling call_on_name.

Now we just need to do something with this name: add it to the list! Remember the SelectView we created? Let's give it a name too:

let select = SelectView::<String>::new()
    .on_submit(on_submit)
    .with_name("select")
    .fixed_size((10, 5));

(Here again, the order is important: we want to wrap the SelectView, not the ResizedView. But we still need to call on_submit before that.)

That way, we can update it with a new item:

fn add_name(s: &mut Cursive) {
    fn ok(s: &mut Cursive, name: &str) {
        s.call_on_name("select", |view: &mut SelectView<String>| {
            view.add_item_str(name);
        });
        s.pop_layer();
    }

    s.add_layer(Dialog::around(EditView::new()
            .on_submit(ok)
            .with_name("name")
            .fixed_width(10))
        .title("Enter a new name")
        .button("Ok", |s| {
            let name = s.call_on_name("name", |v: &mut EditView| {
                v.get_content()
            }).unwrap();
            ok(s, &name);
        })
        .button("Cancel", |s| {
            s.pop_layer();
        }));
}

Now that we know how to access the SelectView, removing an item is not very complicated:

fn delete_name(s: &mut Cursive) {
    let mut select = s.find_name::<SelectView<String>>("select").unwrap();
    match select.selected_id() {
        None => s.add_layer(Dialog::info("No name to remove")),
        Some(focus) => {
            select.remove_item(focus);
        }
    }
}

We use SelectView::selected_id and SelectView::remove_item to remove the item currently selected, nothing too surprising.

But this time, instead of using call_on_name, we use Cursive::find_name: this method returns a handle, through which we can mutate the view. It uses Rc and RefCell under the hood to provide mutable access to the view without borrowing the Cursive root, leaving us free to pop layers.

Conclusion

This tutorial was a bit larger than the previous ones, so take your time, and don't hesitate to read the documentation.

You've now seen:

• How to wrap views to control their size
• How to assemble views together in a linear layout
• How to give names to views and use them later
• How to use SelectView, EditView, Buttons...