Windows Phone 7 App Development

Annoying IsReadOnly bug

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While fixing the security flaw I encountered in WP7.5 FAS I bumped into another annoying issue.

I fixed the FAS issue by hiding the password from view until you drag your finger over it.  When the TextBox has focus the password is displayed as soon as you move away it reverts to showing *********.  Neat and clean!

However the mouse over event can also turn into a Tap event and this causes the WP7 UI to show the on screen keyboard and start editing which is just a UI mess, as all the users is really trying to do is view the information and not change it.  Worse still – quite often the password is shown as ********* for editing!

In order to keep the UI clean I simply set the TextBox to have IsReadOnly=”True” and then the keyboard does not appear.  All seems good – the password is shown when the finger is dragged over it and the UI only drops into edit mode when the user wants to make a change by pressing the Edit button on the toolbar. 

But then during testing my App would sometimes crash when resuming from FAS suspension.  It would show ‘Resuming…’ on the screen and never actually resume…

It took quite a while to establish that it was the IsReadOnly=”True” setting that was causing the problem.

I suspected I could fix it by removing the focus when the App was deactivating but didn’t know how so was pleasantly surprised when the excellent Richard Woo pointed me to the solution when I posted the bug on the App Hub Developer Forum.

I dropped the code into place and the issue is resolved.

public NewItem()
    PhoneApplicationService.Current.Deactivated += new EventHandler<DeactivatedEventArgs>(Current_Deactivated);
/// <summary>
/// Handler to remove focus from a TextBox that is read only.  This cures
/// the exception that occurs when resuming.
/// </summary>
void Current_Deactivated(object sender, DeactivatedEventArgs e)
    var focusedElement = FocusManager.GetFocusedElement();
    if (focusedElement is TextBox)
        if ((focusedElement as TextBox).IsReadOnly == true)

Written by metadevblog

February 13, 2012 at 7:28 pm

Posted in Uncategorized

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