Transition out and in again if showing the same screen twice

Fixes #54

monarch/monarch.lua

@@ -677,16 +677,16 @@ function M.show(id, options, data, cb)
 						-- close all popups, one by one
 						while top.popup do
 							stack[#stack] = nil
-							show_out(top, screen, function()
-								assert(coroutine.resume(co))
-							end)
-							coroutine.yield()
+							show_out(top, screen, callbacks.track())
+							callbacks.yield_until_done()
 							top = stack[#stack]
 						end
 						-- unload and transition out from top
-						-- unless we're showing the same screen as is already visible
-						if top and top.id ~= screen.id then
+						-- wait until we are done if showing the same screen as is already visible
+						local same_screen = top and top.id == screen.id
 						show_out(top, screen, callbacks.track())
+						if same_screen and  then
+							callbacks.yield_until_done()
 						end
 					end
 				end
@@ -817,7 +817,13 @@ function M.is_preloading(id)
 	local screen = screens[id]
 	return screen.preloading
 end
-
+function M.is_preloaded(id)
+	assert(id, "You must provide a screen id")
+	id = tohash(id)
+	assert(screens[id], ("There is no screen registered with id %s"):format(tostring(id)))
+	local screen = screens[id]
+	return screen.preloaded
+end
 
 --- Invoke a callback when a specific screen has been preloaded
 -- This is mainly useful on app start when wanting to show a screen that

monarch/utils/callback_tracker.lua

@@ -7,6 +7,10 @@ function M.create()
 	local callback = nil
 	local callback_count = 0
 
+	local function is_done()
+		return callback_count == 0
+	end
+
 	local function invoke_if_done()
 		if callback_count == 0 and callback then
 			local ok, err = pcall(callback)
@@ -37,6 +41,17 @@ function M.create()
 		invoke_if_done()
 	end
 
+	function instance.yield_until_done()
+		local co = coroutine.running()
+		callback = function()
+			coroutine.resume(co)
+		end
+		invoke_if_done()
+		if not is_done() then
+			coroutine.yield()
+		end
+	end
+
 	return instance
 end
 

test/test_monarch.lua

@@ -405,18 +405,13 @@ return function()
 		end)
 		
 		it("should be able to preload a screen and always keep it loaded", function()
-			monarch.show(SCREEN_PRELOAD, nil, { count = 1 })
+			monarch.show(SCREEN_PRELOAD)
 			assert(wait_until_shown(SCREEN_PRELOAD), "Screen_preload was never shown")
-			-- first time the screen gets loaded it will increment the count
-			assert(monarch.data(SCREEN_PRELOAD).count == 2)
-
-			monarch.show(SCREEN_PRELOAD, { clear = true }, { count = 1 })
-			assert(wait_until_shown(SCREEN_PRELOAD), "Screen_preload was never shown")
-			-- second time the screen gets shown it will already be loaded and not increment the count
-			assert(monarch.data(SCREEN_PRELOAD).count == 1)
+			monarch.back()
+			assert(wait_until_hidden(SCREEN_PRELOAD), "Screen_preload was never hidden")
+			assert(monarch.is_preloaded(SCREEN_PRELOAD))
 		end)
 
-
 		it("should be able to reload a preloaded screen", function()
 			monarch.show(SCREEN_PRELOAD, nil, { count = 1 })
 			assert(wait_until_shown(SCREEN_PRELOAD), "Screen_preload was never shown")