Tabs: Add a way to set the selected tab from the application.

[kudaba]

Add a way for the application to change the selected tab. I was adding functionality to restore window state . Unfortunately while this method works it does have the drawback of not working if the tab doesn't exist yet so I had to use as follows:

foreach (tab) {
    if (ImGui::BeginTabItem(tab)) {
        if (!firstFrame) draw_tab();
        ImGui::EndTabItem();
    }
}

if (firstFrame) ImGui::SetTabItemSelected(selectedTab);

[ocornut]

. Unfortunately while this method works it does have the drawback of not working if the tab doesn't exist yet
"// Due to how tabs are managed, if you call this before the tab exists then the action will get lost. This means you need to add all the tabs first, "

I don't understand this statement, could you clarify?
If there is a bug we could fix the bug and make function works rather than encourage a work-around.

Note that there was a bug fixed in 1.69, a per changelog:
"TabBar: Fixed ImGuiTabItemFlags_SetSelected being ignored if the tab is not visible (with scrolling policy enabled) or if is currently appearing."

Have you checked the ImGuiTabItemFlags_SetSelected flag? (Also see #2410, in that case the user actually only needed ImGuiTabBarFlags_AutoSelectNewTabs).

[kudaba]

Hrm, actually I realize now that I can accomplish the same thing with the flags by simply doing the following:

foreach (tab) {
    var flags = firstFrame && selectedTab == tab ? ImGuiTabItemFlags_SetSelected : 0;
    if (ImGui::BeginTabItem(tab, null, flags)) {
        if (!firstFrame) {
            selecteTab = tab;
            draw_tab();
        }
        ImGui::EndTabItem();
    }
}

I was trying to synchronize my local view of the selected tab with what imgui is doing. The real trick here is to know when it's safe to record the selected tab since there's a frame delay between setting selected and rendering selected.

[ocornut]

Just to clarify: what you are trying to achieve is persist the last focused tab and/or the tab order?

This is in the TODO list as:
- tabs: persistent order/focus in BeginTabBar() api (#261, #351)

[kudaba]

Exactly, I'm slowly expanding on my ability save/load application state. Right now it's restoring last state on startup, but eventually it will be a full layouting sytem to build and share application layouts, so I'll need ways to set various window/control states outside of imguis default save behavior.

[ocornut]

Well, for tab bar we ought to add the saving features (*) and down the line we could eventually pursue adding more persistance features all accross the board (initially expressed in ~#437).

(*) Note that tab bars created by the docking system already have their order saved by the docking system, which go a slightly different route.