ConsolidateSelectedIndex Method

Oct 13, 2025 by wbrum.org 122 views

Introduction

In this article, we will discuss a critical issue in the TabHostView.cs implementation of Xamarin.Forms and MAUI. The problem arises when there are non-selectable tabs with an index less than any of the selectable tabs. This causes the selected tab index to become incorrect, resulting in the wrong tab being displayed.

Reproduces On

The issue can be reproduced on any operating system, device, and SDK version. It is not specific to any particular Xamarin.Forms or MAUI version.

Description

The problem occurs when the TabHostView.cs implementation fails to account for non-selectable tabs when setting the selected tab index. The _selectableTabs list is created by filtering out non-selectable tabs, but this list may not contain all tabs. As a result, the selected tab index is set incorrectly, leading to the wrong tab being displayed.

Implementation Analysis

Let's take a closer look at the implementation in TabHostView.cs.

OnTabItemTapped Method

The OnTabItemTapped method (line 290) sets the selected tab index based on the index of the tapped tab in the _selectableTabs list. However, this approach fails to account for non-selectable tabs that have a lower index than the tapped tab.

private void OnTabItemTapped(object sender, EventArgs e)
{
    // Get the index of the tapped tab in the _selectableTabs list
    int selectedIndex = _selectableTabs.IndexOf(tappedTab);

    // Set the selected tab index
    SelectedIndex = selectedIndex;
}

ConsolidateSelectedIndex Method

The ConsolidateSelectedIndex method (line 705) similarly sets the selected tab index from where the selected tab is found in _selectableTabs.

private void ConsolidateSelectedIndex()
{
    // Get the index of the selected tab in the _selectableTabs list
    int selectedIndex = _selectableTabs.IndexOf(selectedTab);

    // Set the selected tab index
    SelectedIndex = selectedIndex;
}

Repro Steps

To reproduce the behavior, follow these steps:

Open the MauiSample project.
Modify the material underlined tab item at line 84 of TabM.xaml (the 2nd tab) to have IsSelectable = false.
Run the app.
Select the third material tab (the tab with the leading icon).

Expected Result

The view switcher should correctly switch to index 2 and display the label "Leading Icon".

Observed Result

However, the SelectedIndex is set to 1 as this is the index of the 3rd tab in the _selectableTabs list. The displayed label is for the 2nd tab and says "Icon Only" even though the 3rd tab displays as selected.

Conclusion

In conclusion, the issue arises from the implementation of TabHostView.cs failing to account for non-selectable tabs when setting the selected tab index. This results in the wrong tab being displayed. To fix this issue, the implementation should be modified to correctly account for non-selectable tabs.

Recommendations

To resolve this issue, the following recommendations can be made:

Modify the OnTabItemTapped method to correctly account for non-selectable tabs.
Modify the ConsolidateSelectedIndex method to correctly account for non-selectable tabs.
Update the TabHostView.cs implementation to use a more robust approach for setting the selected tab index.

Q&A

Q: What is the issue with the selected tab index in TabHostView.cs? A: The issue arises when there are non-selectable tabs with an index less than any of the selectable tabs. This causes the selected tab index to become incorrect, resulting in the wrong tab being displayed.

Q: Why does the issue occur? A: The issue occurs because the _selectableTabs list is created by filtering out non-selectable tabs, but this list may not contain all tabs. As a result, the selected tab index is set incorrectly, leading to the wrong tab being displayed.

Q: What is the root cause of the issue? A: The root cause of the issue is the implementation of TabHostView.cs failing to account for non-selectable tabs when setting the selected tab index.

Q: How can the issue be reproduced? A: The issue can be reproduced by following these steps:

Open the MauiSample project.
Modify the material underlined tab item at line 84 of TabM.xaml (the 2nd tab) to have IsSelectable = false.
Run the app.
Select the third material tab (the tab with the leading icon).

Q: What is the expected result? A: The view switcher should correctly switch to index 2 and display the label "Leading Icon".

Q: What is the observed result? A: However, the SelectedIndex is set to 1 as this is the index of the 3rd tab in the _selectableTabs list. The displayed label is for the 2nd tab and says "Icon Only" even though the 3rd tab displays as selected.

Q: How can the issue be resolved? A: The issue can be resolved by modifying the OnTabItemTapped method and the ConsolidateSelectedIndex method to correctly account for non-selectable tabs. Additionally, the TabHostView.cs implementation should be updated to use a more robust approach for setting the selected tab index.

Q: What are the recommendations for resolving the issue? A: The following recommendations can be made:

Modify the OnTabItemTapped method to correctly account for non-selectable tabs.
Modify the ConsolidateSelectedIndex method to correctly account for non-selectable tabs.
Update the TabHostView.cs implementation to use a more robust approach for setting the selected tab index.

Q: What are the benefits of resolving the issue? A: Resolving the issue will result in the correct tab being displayed, and the selected tab index will be set correctly. This will improve the overall user experience and ensure that the app functions as expected.

Q: How can the issue be prevented in the future? A: To prevent the issue in the future, it is recommended to thoroughly test the app and ensure that the selected tab index is set correctly. Additionally, the implementation of TabHostView.cs should be reviewed and updated to use a more robust approach for setting the selected tab index.