Confused on the purpose of TabIndexs List

[dasien]

Hello,

I was hoping to get some clarity on the purpose of the View.TabIndexes list. What i was trying to accomplish was to join two views together, and have the first control on View2 TabIndex be + 1 from the last control in View1.TabIndexes.

What i am finding is that regardless of what i put for the TabIndex value for controls in View 1, even if i say that certain controls have no TabIndex and i set the TabStop to false, the views with no TabIndex and TabStop set to false are still listed in the TabIndexes list which inflates the list with controls. As a consequence, the value i put in for TabIndex for controls which i want to interact with the Tab key is overridden by their order in the TabIndexes list.

Thus, if i have a view with a Label with TabStop = false and nothing set for TabIndex, and a TextField with TabStop = true and TabIndex = 1, and I repeat that pattern say 3 times incrementing the TabIndex by 1 for each TextField so the next TextField.TabIndex = 2 then 3, etc. the values reported for the TextField in the parent View.Tablndexes list is 1,3,5,7 respectively rather than the 1,2,3,4 i set.

I am confused why something is overwriting my set TabIndex values on controls at all and if there is a way for me to turn that off. I could understand the system taking a best guess if i don't put values in and don't also turn off the fact that a particular View should be a tab stop, but it is overwriting the values which are present and making it difficult for me to compute the correct TabIndex of a joined View.

[BDisp]

Label by default has CanFocus as false. Thus setting the TabIndex or TabStop has no influence. Also I think that is preferred set that properties after the views are added to their superviews and before run the application. If still it doesn't have the index you are setting please post a sample app that reproduce the issue, please.

[dasien]

Hi BDisp,

I did some testing last night with some sample code and the results were somewhat as you suggested, but in other ways strange. I created three Label and three TextField views, and laid them out in three rows like so Label Textfield. It seems like the engine goes from top left to lower right as it decides the TabIndex order of "tab-able" controls, is that right? I only say that because my first run was without any intervention (i.e. not setting the TabIndex property at all resulted in the TabIndexs List sowing an element pattern of Label then TextField, 3 times. The Label all had a TabIndex of -1, which i assume means that they are not to respond to Tab keys (because they don't take focus by default). The TextField had 1,3,5 for their respective TabIndex properties, which makes sense given that i didn't pass any value in and they are the [1],[3], and [5] element in the TabIndexes IList.

For my second run, i added a value to the TabIndex for each TextField and then added them to the View. Again, as you indicated, the values i added were overridden by whatever the layout engine determined to be appropriate, and the values remained 1,3,5 for the TabIndex of the TextField controls.

Where things get strange is when i add the TextField to the View then set the TabIndex property. If i set those values to 0,1,2 for TextField 1, 2, and 3 respectively, The TabIndexes List shows the TextField in order in the first three elements of the List and the Label i the last three places. This has the unfortunate side effect of - in my use case - when i look at the View.TabIndexes.Last() which ostensibly be the last TabIndex, what is in that last position is a Label with a TabIndex of -1.

Interestingly, if i set the values for TabIndex on the TextField to 3,4,5, after setting those controls to the View the resulting TabIndexes list shows Label1 in element [0] in the list, then TextField 1 & 2 as the [1] and [2] elements, then two Label as [3] and [4] and finally TextField3 as [5]. In this case, the underlying system chose to overwrite the values after they were set to the View of two of the three TextFields, and leave the third as it was set.

I will paste the code below with the last test values set. A breakpoint on the line IList < View > indexes = this.TabIndexes; will show the order that the system puts controls.

In the end, i am sure there is a predictable method to the way the system is ordering controls, but it seems rather arbitrary from the outside, and the TabIndexes list seems tightly coupled to the controls on a view - whether they can be tabbed to or not. Having the [n]th element of a list sometimes equal the value of the TabIndex of the View it represents and sometimes not (in the case of Label and maybe other Views which are by default not focus-able in which case it is -1) is confusing and limits the value of the list to a client.

using Terminal.Gui;

namespace TabIndexTest 
{
    public class TabIndexView : Toplevel
    {
        private Label label1;
        private TextField textField1;
        private Label label2;
        private TextField textField2;
        private Label label3;
        private TextField textField3;
        public TabIndexView() 
        {
            
            InitializeComponent(true);
            
            // Show values for tabindex of textfields.
            IList < View > indexes = this.TabIndexes;
        }
        
        private void InitializeComponent(bool tabindexaftervew ) {
            textField3 = new TextField();
            label3 = new Label();
            textField2 = new TextField();
            label2 = new Label();
            textField1 = new TextField();
            label1 = new Label();
            Width = Dim.Fill(0);
            Height = Dim.Fill(0);
            X = 0;
            Y = 0;
            Visible = true;
            Modal = false;
            IsMdiContainer = false;
            TextAlignment = TextAlignment.Left;
            label1.Width = 4;
            label1.Height = 1;
            label1.X = 1;
            label1.Y = 1;
            label1.Visible = true;
            label1.Data = "label1";
            label1.Text = "Tabstop for Textfield 1";
            label1.TextAlignment = TextAlignment.Left;
            Add(label1);
            textField1.Width = 10;
            textField1.Height = 1;
            textField1.X = 55;
            textField1.Y = 1;
            textField1.Visible = true;
            textField1.Secret = false;
            textField1.Data = "textField1";
            textField1.Text = "";
            textField1.TextAlignment = TextAlignment.Left;

            if (tabindexaftervew)
            {
                Add(textField1);
                textField1.TabIndex = 3;
            }

            else
            {
                textField1.TabIndex = 3;
                Add(textField1);
            }
            
            label2.Width = 4;
            label2.Height = 1;
            label2.X = 1;
            label2.Y = 2;
            label2.Visible = true;
            label2.Data = "label2";
            label2.Text = "Tabstop for textfield 2";
            label2.TextAlignment = TextAlignment.Left;
            Add(label2);
            textField2.Width = 10;
            textField2.Height = 1;
            textField2.X = 55;
            textField2.Y = 2;
            textField2.Visible = true;
            textField2.Secret = false;
            textField2.Data = "textField2";
            textField2.Text = "";
            textField2.TextAlignment = TextAlignment.Left;
            
            if (tabindexaftervew)
            {
                Add(textField2);
                textField2.TabIndex = 4;
            }

            else
            {
                textField2.TabIndex = 4;
                Add(textField2);
            }
            
            label3.Width = 4;
            label3.Height = 1;
            label3.X = 1;
            label3.Y = 3;
            label3.Visible = true;
            label3.Data = "label3";
            label3.Text = "Tabstop for textfield 3";
            label3.TextAlignment = TextAlignment.Left;
            Add(label3);
            textField3.Width = 10;
            textField3.Height = 1;
            textField3.X = 55;
            textField3.Y = 3;
            textField3.Visible = true;
            textField3.Secret = false;
            textField3.Data = "textField3";
            textField3.Text = "";
            textField3.TextAlignment = TextAlignment.Left;
            
            if (tabindexaftervew)
            {
                Add(textField3);
                textField3.TabIndex = 5;
            }

            else
            {
                textField3.TabIndex = 5;
                Add(textField3);
            }

            Width = 43;
            Height = 12;
            X = 26;
            Y = 11;
            Visible = true;
            Data = "view";
            TextAlignment = TextAlignment.Left;
            
        }
    }
}

[tig]

Is this v1?

I think there's a bug in the Toplevel code that erroneously re-orders the subviews of a toplevel screwing up tabindex. I fixed this in v2 but forgot to do it in v1. I'm not at a computer right now but it would explain what you're seeing.

[dasien]

Hi - yes this is v1. Sorry i should have indicated that.

[dasien]

Hi - i was just curious if this was something that could be fixed in v1, or if i should wait and move to v2. It would certainly help to have the tab order be controllable.

[BDisp]

I found the bug and I'll submit a PR with a fix. But for your example work you must set the tabindex after all views are added to the superview and not by setting only after add one at a time. So after all the views are added then set the tabindex for them. In the v2 the bug also exist and I'll submit a PR for him too. Remember that the order index isn't continuous because all the tabindexes that have a value of -1 are ignored. So, it may have 1, 3, 5, etc... If you want only a ordered of all tabindexes you filter them, like TabIndexes.Select(t => t > -1).

[BDisp]

Here is the fix #3352.

[BDisp]

@dasien here is a proof about what I've said.

		[Fact]
		public void TabIndex_Invert_Order_Added_One_By_One_Does_Not_Do_What_Is_Expected ()
		{
			var r = new View ();
			var v1 = new View () { Id = "1", CanFocus = true };
			r.Add (v1);
			v1.TabIndex = 2;
			var v2 = new View () { Id = "2", CanFocus = true };
			r.Add (v2);
			v2.TabIndex = 1;
			var v3 = new View () { Id = "3", CanFocus = true };
			r.Add (v3);
			v3.TabIndex = 0;

			Assert.False (r.TabIndexes.IndexOf (v1) == 2);
			Assert.True (r.TabIndexes.IndexOf (v1) == 1);
			Assert.False (r.TabIndexes.IndexOf (v2) == 1);
			Assert.True (r.TabIndexes.IndexOf (v2) == 2);
			// Only the last is in the expected index
			Assert.True (r.TabIndexes.IndexOf (v3) == 0);

			Assert.True (r.Subviews.IndexOf (v1) == 0);
			Assert.True (r.Subviews.IndexOf (v2) == 1);
			Assert.True (r.Subviews.IndexOf (v3) == 2);
		}

[dasien]

Hi @BDisp. Thank you for the update and the fix! I am curious what the purpose of the TabIndexes list is. For my purpose, i was trying to adjust the tab order of controls after a 'View' was added to a base view. In other words, i have a 'View' with some common elements which will always show, and a "detail" view which i embed in the middle of the base View (from a visual perspective). Because i don't know which of the detail views might be loaded (they have a different number of controls in each), and because i want the user to be able to tab through all the controls in order, i need to adjust the tab index of the "footer" controls in the base View after the detail view has been inserted.

What i had been doing was getting that TabIndexes list and just setting the tab index of the first footer control to TabIndexes.Count + 1, but that isn't really correct. It sounds like i need to find the highest value in that List, not simply the count, because there are Label controls in there and others, which have -1 as their value.

I will only adjust the values after all controls have been loaded, as you instruct and see the effect. Thanks again for the fix!

[BDisp]

Hi @BDisp. Thank you for the update and the fix! I am curious what the purpose of the TabIndexes list is. For my purpose, i was trying to adjust the tab order of controls after a 'View' was added to a base view. In other words, i have a 'View' with some common elements which will always show, and a "detail" view which i embed in the middle of the base View (from a visual perspective). Because i don't know which of the detail views might be loaded (they have a different number of controls in each), and because i want the user to be able to tab through all the controls in order, i need to adjust the tab index of the "footer" controls in the base View after the detail view has been inserted.

TabIndexes list is someway as the SubViews list, but order by the TabIndex property, which values equal to -1 are ignored. The SubViews list ares order by the added views for redraw in the Z-Order. When the TabIndex is set before the view is added it set the value to 0 because the SuperView is null. If you want the same order as views are being added you don't need to set the TabIndex.

What i had been doing was getting that TabIndexes list and just setting the tab index of the first footer control to TabIndexes.Count + 1, but that isn't really correct. It sounds like i need to find the highest value in that List, not simply the count, because there are Label controls in there and others, which have -1 as their value.

If you want to control the TabIndexes value yourself then you must set the value to view.TabIndex = TabIndexes.IndexOf (view); after the view is added to the superview, but the Add already do that automatically.

I will only adjust the values after all controls have been loaded, as you instruct and see the effect. Thanks again for the fix!

Yes, but only if you need to do that. e.g. you may need to add a view2 first than the view1 to use Pos/Dim of the view2, but you want the TabIndex of the view1 bigger than the TabIndex of the view2. In this case you have to set the TabIndex value accordingly.