Tutorial Callback On Drag

This callback is activated when a widget is left mouse clicked and the click is not released. As long as the click is not released, the widget will receive a new event every time the mouse cursor changes position.

The callback receives two extra arguments: one is the previous drag position, and one is the current drag position. The previous drag position argument is an Option; on the very first drag event, the previous drag position will be None. This is how you know the drag is new. Subsequently, the previous drag position will contain IsizeCoordinates. Because you have both the current and the previous IsizeCoordinates, you know which direction the drag is going.

The coordinates are relative to the widget. So if the coordinates are (3, 2), it means the click was located in the widget on the third pixel from the left and the second pixel from the top. It is possible for drag coordinates to be negative, which means the drag is occurring to the left of, or above, the widget. The coordinates can also be larger than the widget, which means the drag is occurring to the right of, or below, the widget. You can access the coordinates through 'mouse_pos.x' and 'mouse_pos.y'.

To set this callback with a closure:

use ez_term::*;
let (root_widget, mut state_tree, mut scheduler) = load_ui();

let my_callback = move |context: Context, previous_mouse_pos: Option<IsizeCoordinates>,
                        mouse_pos: IsizeCoordinates| {

    true
};
let new_callback_config = CallbackConfig::from_on_drag(Box::new(my_callback));
scheduler.update_callback_config("my_label", new_callback_config);

To set this callback with a function:

use ez_term::*;
let (root_widget, mut state_tree, mut scheduler) = load_ui();

fn my_callback(context: Context, previous_mouse_pos: Option<IsizeCoordinates>,
               mouse_pos: IsizeCoordinates) -> bool {

    true
};
let new_callback_config = CallbackConfig::from_on_drag(Box::new(my_callback));
scheduler.update_callback_config("my_label", new_callback_config);

Continue

The general tutorial continues with: Callback: On Scroll up.