Callbacks & persistence#

#Overview

WebGridCanvas exposes 4 callbacks for reacting to user-driven mutations. They're the primitives you need to persist grid state to localStorage, a backend, or any external sink. The grid itself never persists — that choice is left to the caller.

#Available callbacks

#Persisting column layout

set_on_columns_changed fires after every layout-mutating command. Combine with the 3 layout readers to snapshot the state.

#Readers

pub fn column_widths(&self) -> Vec<(String, f64)>;  // (col_key, px)
pub fn column_order(&self) -> Vec<String>;          // col_keys in display order
pub fn pinned_count(&self) -> usize;

#Example: localStorage

use rs_grid_leptos::WebGridCanvas;
use web_sys::window;

let on_mount = move |gc: WebGridCanvas| {
    let gc_save = gc.clone();
    gc.set_on_columns_changed(move || {
        let payload = (
            gc_save.column_widths(),
            gc_save.column_order(),
            gc_save.pinned_count(),
        );
        if let Ok(json) = serde_json::to_string(&payload) {
            if let Some(ls) = window()
                .and_then(|w| w.local_storage().ok().flatten())
            {
                let _ = ls.set_item("rs-grid-layout", &json);
            }
        }
    });
};

On mount, read the stored JSON and apply it by:

• Widths — set ColumnDef.width before building the GridModel
• Order — sort model.columns to match the persisted order
• Pinned count — set model.pinned_count directly (or via set_pinned_count after mount)

After mutating widths or order in model.columns, recompute the precomputed offsets used by hit-testing:

model.column_offsets = rs_grid_core::ColumnOffsets::compute(&model.columns);

The examples/basic-leptos/src/lib.rs example ships a complete load/save/apply flow you can copy.

#Scope of set_on_columns_changed

The callback covers physical layout only: widths, order, pin count. It does not fire on ToggleSort, SetSort, ClearSort, SetColumnFilter, or ClearAllFilters — those have no dedicated callback yet. Persist sort/filter state separately if you need it.

It also fires on CommitColumnResize (once at mouseup), not on every intermediate ResizeColumn during a drag — so writes to localStorage stay infrequent without any throttling on your side.

#Re-entrancy

⚠️ Do not dispatch a GridCommand synchronously from any callback. The callback runs while the grid's internal state is still borrowed read-only — dispatching would re-borrow and panic. Defer via queueMicrotask, setTimeout(0), or a channel if you need to react with another command.