diff --git a/src/ltui/boxdialog.lua b/src/ltui/boxdialog.lua
index 7d17d28..125b65c 100644
--- a/src/ltui/boxdialog.lua
+++ b/src/ltui/boxdialog.lua
@@ -40,7 +40,6 @@ function boxdialog:init(name, bounds, title)
     self:text():bounds().ey = self._TEXT_EY
     self:text():invalidate(true)
     self:text():option_set("selectable", false)
-    self:text():option_set("scrollable", false)
 
     -- insert box
     self:panel():insert(self:box())
diff --git a/src/ltui/inputdialog.lua b/src/ltui/inputdialog.lua
index f05744f..1571eca 100644
--- a/src/ltui/inputdialog.lua
+++ b/src/ltui/inputdialog.lua
@@ -45,7 +45,6 @@ function inputdialog:init(name, bounds, title)
     self:text():bounds().ey = 1
     self:text():invalidate(true)
     self:text():option_set("selectable", false)
-    self:text():option_set("scrollable", false)
 
     -- text changed
     self:text():action_set(action.ac_on_text_changed, function (v)
diff --git a/src/ltui/mconfdialog.lua b/src/ltui/mconfdialog.lua
index 1857131..d4a2e08 100644
--- a/src/ltui/mconfdialog.lua
+++ b/src/ltui/mconfdialog.lua
@@ -122,6 +122,7 @@ function mconfdialog:helpdialog()
     if not self._HELPDIALOG then
         local helpdialog = textdialog:new("mconfdialog.help", self:bounds(), "help")
         helpdialog:button_add("exit", "< Exit >", function (v) helpdialog:quit() end)
+        helpdialog:option_set("scrollable", true)
         self._HELPDIALOG = helpdialog
     end
     return self._HELPDIALOG
@@ -132,6 +133,7 @@ function mconfdialog:resultdialog()
     if not self._RESULTDIALOG then
         local resultdialog = textdialog:new("mconfdialog.result", self:bounds(), "result")
         resultdialog:button_add("exit", "< Exit >", function (v) resultdialog:quit() end)
+        resultdialog:option_set("scrollable", true)
         self._RESULTDIALOG = resultdialog
     end
     return self._RESULTDIALOG
diff --git a/src/ltui/scrollbar.lua b/src/ltui/scrollbar.lua
index cc64115..8f22290 100644
--- a/src/ltui/scrollbar.lua
+++ b/src/ltui/scrollbar.lua
@@ -35,7 +35,7 @@ function scrollbar:init(name, bounds, vertical)
     view.init(self, name, bounds)
 
     -- init bar attribute
-    self:charattr_set("black")
+    self:charattr_set("black on black")
 
     -- init bar vertical
     self:vertical_set(vertical)
@@ -165,14 +165,18 @@ function scrollbar:on_draw(transparent)
     if self:vertical() then
         local sb = math.floor(self:height() * pb)
         local se = math.ceil(self:height() * pe)
-        if se > sb and se - sb < self:height() then
-            self:canvas():attr(charattr):move(0, sb):putchar(char, se - sb, true)
+        if se > sb and se - sb <= self:height() then
+            for x = 0, self:width() - 1 do
+                self:canvas():attr(charattr):move(x, sb):putchar(char, se - sb, true)
+            end
         end
     else
         local sb = math.floor(self:width() * pb)
         local se = math.ceil(self:width() * pe)
-        if se > sb and se - sb < self:width() then
-            self:canvas():attr(charattr):move(sb, 0):putchar(char, se - sb)
+        if se > sb and se - sb <= self:width() then
+            for y = 0, self:height() - 1 do
+                self:canvas():attr(charattr):move(sb, y):putchar(char, se - sb)
+            end
         end
     end
 end
diff --git a/src/ltui/textarea.lua b/src/ltui/textarea.lua
index bdd5d57..296e3e3 100644
--- a/src/ltui/textarea.lua
+++ b/src/ltui/textarea.lua
@@ -25,7 +25,6 @@ local label     = require("ltui/label")
 local event     = require("ltui/event")
 local curses    = require("ltui/curses")
 local action    = require("ltui/action")
-local scrollbar = require("ltui/scrollbar")
 
 -- define module
 local textarea = textarea or label()
@@ -39,9 +38,6 @@ function textarea:init(name, bounds, text)
     -- mark as selectable
     self:option_set("selectable", true)
 
-    -- mark as scrollable
-    self:option_set("scrollable", true)
-
     -- init start line
     self._STARTLINE = 0
     self._LINECOUNT = 0
@@ -61,17 +57,6 @@ function textarea:on_draw(transparent)
     if strs and #strs > 0 and textattr then
         self:canvas():attr(textattr):move(0, 0):putstrs(strs, self._STARTLINE + 1)
     end
-
-    -- draw scrollable
-    if self:option("scrollable") then
-        local tb = self._STARTLINE
-        local fator = self:height() / self._LINECOUNT
-        local sb = math.min(math.floor(tb * fator), self:height() - 1)
-        local se = math.min(sb + math.ceil(self:height() * fator), self:height())
-        if se > sb and se - sb < self:height() then
-            self:canvas():attr("black"):move(self:width() - 1, sb):putchar(' ', se - sb, true)
-        end
-    end
 end
 
 -- set text
diff --git a/src/ltui/textdialog.lua b/src/ltui/textdialog.lua
index d8fca4e..892c9ad 100644
--- a/src/ltui/textdialog.lua
+++ b/src/ltui/textdialog.lua
@@ -19,13 +19,14 @@
 --
 
 -- load modules
-local log      = require("ltui/base/log")
-local rect     = require("ltui/rect")
-local event    = require("ltui/event")
-local dialog   = require("ltui/dialog")
-local curses   = require("ltui/curses")
-local textarea = require("ltui/textarea")
-local action   = require("ltui/action")
+local log       = require("ltui/base/log")
+local rect      = require("ltui/rect")
+local event     = require("ltui/event")
+local dialog    = require("ltui/dialog")
+local curses    = require("ltui/curses")
+local textarea  = require("ltui/textarea")
+local scrollbar = require("ltui/scrollbar")
+local action    = require("ltui/action")
 
 -- define module
 local textdialog = textdialog or dialog()
@@ -36,9 +37,15 @@ function textdialog:init(name, bounds, title)
     -- init window
     dialog.init(self, name, bounds, title)
 
+    -- mark as scrollable, disabled by default
+    self:option_set("scrollable", false)
+
     -- insert text
     self:panel():insert(self:text())
 
+    -- insert scrollbar
+    self:panel():insert(self:scrollbar())
+
     -- select buttons by default
     self:panel():select(self:buttons())
 
@@ -48,6 +55,24 @@ function textdialog:init(name, bounds, title)
     end)
 end
 
+-- enable or disable scrollbar
+function textdialog:option_set(name, value)
+    if name == "scrollable" then
+        local oldvalue = self:option(name)
+        if value ~= oldvalue then
+            if value then
+                self:text():bounds():resize(self:panel():width() - 1, self:panel():height() - 1)
+                self:scrollbar():show(true)
+            else
+                self:text():bounds():resize(self:panel():width(), self:panel():height() - 1)
+                self:scrollbar():show(false)
+            end
+            self:invalidate()
+        end
+    end
+    dialog.option_set(self, name, value)
+end
+
 -- get text
 function textdialog:text()
     if not self._TEXT then
@@ -56,6 +81,15 @@ function textdialog:text()
     return self._TEXT
 end
 
+-- get scrollbar
+function textdialog:scrollbar()
+    if not self._SCROLLBAR then
+        self._SCROLLBAR = scrollbar:new("textdialog.scrollbar", rect:new(self:panel():width() - 1, 0, 1, self:panel():height() - 1))
+        self._SCROLLBAR:show(false)
+    end
+    return self._SCROLLBAR
+end
+
 -- on event
 function textdialog:on_event(e)
 
diff --git a/src/ltui/textedit.lua b/src/ltui/textedit.lua
index 978eccf..0acef24 100644
--- a/src/ltui/textedit.lua
+++ b/src/ltui/textedit.lua
@@ -47,9 +47,6 @@ function textedit:init(name, bounds, text)
     self:option_set("mouseable", true)
     self:action_set(action.ac_on_clicked, function () return true end)
 
-    -- disable scrollbar
-    self:option_set("scrollable", false)
-
     -- enable multiple line
     self:option_set("multiline", true)
 end
diff --git a/tests/dialog.lua b/tests/dialog.lua
index 823ca00..1e8371d 100644
--- a/tests/dialog.lua
+++ b/tests/dialog.lua
@@ -86,6 +86,7 @@ function demo:dialog_help()
             dialog_help:text():text_set(helptext)
         end
         dialog_help:button_add("exit", "< Exit >", function (v) self:remove(dialog_help) end)
+        dialog_help:option_set("scrollable", true)
         self._DIALOG_HELP = dialog_help
     end
     return dialog_help