feat(example): add userdata example

Similar to lvgl user_data, the lua lvgl obj also have user_data for user. It uses userdata's uservalue for this purpose.

Signed-off-by: Neo Xu <neo.xu1990@gmail.com>

examples/examples.lua

@@ -43,5 +43,6 @@ createBtn(container, "keyboard")
 createBtn(container, "animation")
 createBtn(container, "pointer")
 createBtn(container, "analogTime")
+createBtn(container, "userdata")
 createBtn(container, "flappyBird/flappyBird")
 createBtn(container, "tests")

examples/userdata.lua

@@ -0,0 +1,29 @@
+-- user_data can store any type of lua value
+local obj1 = lvgl.Label {
+    text_color = "#333",
+    border_color = "#f00",
+    border_width = 1,
+    align = lvgl.ALIGN.TOP_LEFT
+}
+
+obj1.user_data = 123.456
+obj1.text = "user_data:\n" .. obj1.user_data
+
+-- use user_data to store table
+local obj2 = lvgl.Label {
+    text_color = "#333",
+    border_color = "#f00",
+    border_width = 1,
+    align = lvgl.ALIGN.TOP_RIGHT
+}
+
+obj2.user_data = {
+    abc = "hello",
+    def = "world",
+    [1] = 123,
+}
+obj2.text = "user_data:"
+for k, v in pairs(obj2.user_data) do
+    print(k, v)
+    obj2.text = obj2.text .. string.format("%s: %s\n", k, v)
+end