@Html.CheckBoxFor() falls back to values in ViewDataDictionary

[dougbu]

When the expression result is null e.g. in a Create view, @Html.CheckBoxFor() finds value (if any) in the ViewDataDictionary. This is incorrect and inconsistent with other HTML helpers. Expression-based helpers should not use ViewDataDictionary and the rest do not.

[dougbu]

E.g. the following in a create view

ViewData["Alive"] = true;
...
<td>
    @Html.LabelFor(m => m.Alive)
</td>
<td>
    @Html.CheckBoxFor(m => m.Alive)
    or
    @Html.RadioButtonFor(m => m.Alive, value: false) False
    @Html.RadioButtonFor(m => m.Alive, value: true) True
</td>

results in

The checkbox should not be selected. The radio button by contrast correctly shows the expression result is neither true or false.

[dougbu]

This bug also affects the <input type="checkbox"/> tag helper.

Workarounds include not adding entries to ViewDataDictionary or avoiding null containers in the model (!!).

Fix is to change one line to ensure useViewData passed to DefaultHtmlGenerator.GenerateInput() is always false in CheckBoxFor() scenarios. Could back-port this fix to MVC 5.2 (bug was inherited) as well.

[yishaigalatzer]

Remove the sample and

[dougbu]

Fixed via 12565da