Difference between revisions of "Tutorial:LuaFormListView"

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(Using OnCustomDrawItem, OnCustomDrawSubItem)
(Using OnCustomDrawItem, OnCustomDrawSubItem)
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I think they can also be used to do other drawing.
 
I think they can also be used to do other drawing.
  
<pre style="background-color: #ff6677; color: white">Warning!
+
<pre style="background-color: #ff4655; color: white; white-space: pre-wrap">Warning!
  
 
I have CE become unresponsive sometimes, I think it's best to close the editor when saving changes to these methods.  You can still leave the form open to see changes, just not the editor.  I think it is changing the item array and item count with the custom data most likely.</pre>
 
I have CE become unresponsive sometimes, I think it's best to close the editor when saving changes to these methods.  You can still leave the form open to see changes, just not the editor.  I think it is changing the item array and item count with the custom data most likely.</pre>

Revision as of 02:02, 23 July 2018


This will be concentrating on the ListView control, check out this tutorial to learn more about working with forms in general.

Initial Setup

The Form

To get started create a form with Table->Create form, this generated a UDF1 form for me. Now click the ListView button and drag an area on the form to set its extends.

Add ListView

In the properties change the ViewStyle to vsReport, this gives us a normal view with rows and columns. Also change ReadOnly to true because we won't allow editing, and RowSelect to true so clicking will select an entire row instead of just one column value:

ListView ReadOnly, RowSelect, and ViewStyle

Adding a Column

Now let's add a column. Click on the Columns property and the '...' to the right to open the column editor and click 'Add' to add a new column. Here I set the Caption of the column to 'Message' and changed the Width from 50 to 200. You can also change the width by dragging the column separator on the design form.

ListView Add One Column

Add Items

Now close design mode by clicking the X on the top right of the toolbar window and the form will display in normal mode. Execute this code:

local items = UDF1.CEListView1.Items
items.Clear()
local item = items.Add()
item.Caption = "First item"
item = items.Add()
item.Caption = "Second item"

That will clear the list and add a couple of items that you can see:

ListView Sample One Column Values

Adding More Columns

Now I'll go back to the properties of CEListView1 and click on the '...' in the Columns property to open the column editor and click Add to add a couple of more columns and edit their Caption properties to be Extra and Clock.

ListView Add More Columns

Add Data For New Columns

A TListItem has the value for the first column in the Caption property. The data for other columns is stored in the SubItems property as a Strings object. I find it easiest to update by setting the 'Text' property to a list of strings with linebreaks. You can use table.concat(<table>,'\n') to do this for a LUA array and it'll call tostring() on the values.

local items = UDF1.CEListView1.Items
items.Clear()
local item = items.Add()
item.Caption = "First item"
item.SubItems.text = "Hello\n"..tostring(os.clock())
item = items.Add()
item.Caption = "Second item"
item.SubItems.text = table.concat({"World",os.clock()}, '\n')

ListView Add More Columns

Using OwnerData

What if you have a LOT of items you want to display? There's overhead with creating the items and I couldn't get BeginUpdate/EndUpdate to work. That's where the OwnerData property comes in! Check the OwnerData property of the ListView to make it True. Change the Object Inspector tab from Properties to Events and double-click on the OnData property to create an event handler. Now I'll change the table script to look like this and run it:

-- items
list = {}
for i=1,1000000 do
  local item = {
    message = string.format('Message %d', i),
    data = math.sqrt(i)
  }
  table.insert(list, item)
end

-- need to set the Items.Count property so that it knows how many rows there
-- are in total
UDF1.CEListView1.Items.Count = #list

-- definition created by double-clicking OnData event handler
function CEListView1Data(sender, listitem)
  -- use + 1 because listitem.Index is 0-based
  local d = list[listitem.Index + 1]
  if not d then return end
  listitem.Caption = d.message -- first column
  -- other columns have sqrt of data property and CURRENT clock
  -- when this event was called
  local others = {string.format('%0.3f', math.sqrt(d.data)), os.clock()}
  listitem.SubItems.text = table.concat(others, '\n')
end

So we set UDF1.CEListView1.Items.Count to the number of items the ListView should display. The OnData event handler will be called for each displayed row. When the displayed row changes, the method is called again. This way it is called just for the visible rows in the control.

You can tell it's getting called by scrolling down one row then back up, the 'Clock' column value will change. If you resize the form (and have the anchors set so the ListView will resize) then they all change. You can also see it when selecting or deselecting rows because it needs to be redrawn.

The list[index].data property is actually the square root of the index and the handler sets the actual displayed value to the square root of that, so you can see Message 16 has an Extra value of 2.000.

ListView Add More Columns

Aside on syncing with lua

If you see something you don't expect, it could be that the event handlers are using old functions. Try these steps:

  1. Close down the designer and the form
  2. Run your script that creates the functions used by the form events
  3. Click Table=>Resynchronize forms with lua

Using OnCustomDrawItem, OnCustomDrawSubItem

If you want to change the style of items you can use the OnCustomDrawItem and OnCustomDrawSubItem events. These can alter the styles as shown here and CE will draw the text as normal if you return true, but I think they can also be used to do other drawing.

Warning!

I have CE become unresponsive sometimes, I think it's best to close the editor when saving changes to these methods.  You can still leave the form open to see changes, just not the editor.  I think it is changing the item array and item count with the custom data most likely.

OnCustomDrawItem

CustomDrawItem(Sender, Item, State)

This is called for the first column that displays the Caption. If you change a style here it will be set for other columns as well. Sender is the ListView control, Item is the ListItem, and I'm not sure what State is. Here's a sample that will draw odd rows (0-based) with a blue background:

function CEListView1CustomDrawItem(Sender, Item, State)
  if (Item.Index % 2) == 1 then
    Sender.Canvas.Brush.Color = 0xffe0e0 -- odd rows blue bg (0-based)
  else
    Sender.Canvas.Brush.Color = 0xffffff -- other rows white bg red fg
    Sender.Canvas.Font.Color = 0x4040ff
  end
  return true --return true for DefaultDraw
end

Drawing odd rows blue bg, even red fg


OnCustomDrawSubItem

This is called for columns other than the first. You should have OnCustomDrawItem set as well to handle the first column, and I think it's best just to have it delegate to this method. The value are the same except for a new SubItem parameter that is the zero-based column index.

function CEListView1CustomDrawSubItem(Sender, Item, SubItem, State)
  if (Item.Index % 2) == 1 then
    Sender.Canvas.Brush.Color = 0xffe0e0 -- odd rows blue bg (0-based)
    if SubItem == 1 then Sender.Canvas.Font.Color = 0x8f8f8f end -- gray middle column
  else
    Sender.Canvas.Brush.Color = 0xffffff -- odd rows white bg (0-based)
    if SubItem == 2 then
      Sender.Canvas.Font.Color = 0xffff40 -- cyan right column
    else
      Sender.Canvas.Font.Color = 0x2020ff -- red other columns
    end
  end
  return true -- return true for DefaultDraw
end

function CEListView1CustomDrawItem(Sender, Item, State)
  return CEListView1CustomDrawSubItem(Sender, Item, 0, State)
end

Style Columns