Empty

Empty reserves a place in the page and hands back a slot to write it with. Writing the slot again takes the previous contents off the screen instead of adding to them, which is what lets a page function show progress and then replace it with the result.

Usage

func Empty(c *tgframe.Container, conf ...*EmptyConf) *EmptySlot

• c: Parent container.
• conf: Optional configuration, at most one.

// EmptyConf is the configuration for the Empty component.
type EmptyConf struct {
	tgframe.Base // ID
}

The container an empty hands out derives its id from the empty's; give none and it carries none, and the components inside are still placed by position.

The slot has two methods:

// With writes what f adds into the slot, over whatever it held.
func (s *EmptySlot) With(f func(c *tgframe.Container))

// Clear takes what the slot holds off the screen.
func (s *EmptySlot) Clear()

EmptySlot was called EmptyContainer; the old name is kept as a deprecated alias. See what a component hands back.

The container With hands over lives until the next With or Clear. Writing into it after that puts components under a node the client no longer has, so take it in the callback rather than keeping it.

Example

	slot := tgcomp.Empty(p.Main, &tgcomp.EmptyConf{ID: "query_result"})
	slot.With(func(c *tgframe.Container) {
		tgcomp.Text(c, "No query yet.")
	})

	if tgcomp.Button(p.Main, "Run a slow query") {
		slot.With(func(c *tgframe.Container) {
			tgcomp.Text(c, "Querying…")
		})

		time.Sleep(3 * time.Second)

		slot.With(func(c *tgframe.Container) {
			tgcomp.Table(c,
				[]string{"table", "rows"},
				[][]string{{"users", "1289"}, {"orders", "4021"}})
		})
	}

Ids and state

A widget in a slot claims its id the same way it would anywhere else, and gives it back when the slot is cleared. So the same widget may be written into one slot as many times as the page likes without the run failing with duplicated component id:

slot := tgcomp.Empty(p.Main)
for range names {
	slot.With(func(c *tgframe.Container) {
		tgcomp.Textbox(c, "Name")
	})
}

A widget that is cleared and not written again is gone from the page, and its state goes with it: the value it held is dropped at the end of the run, rather than turning up in whatever lands on that id next run.

The slot also starts empty on every run, whatever the last run left in it.