Bug 24054 - BindableObject.ApplyBindings is broken when the old bindingcontext was null
Summary: BindableObject.ApplyBindings is broken when the old bindingcontext was null
Alias: None
Product: Forms
Classification: Xamarin
Component: Forms ()
Version: 1.3.0
Hardware: Macintosh Mac OS
: Normal normal
Target Milestone: ---
Assignee: Eric Maupin
Depends on:
Reported: 2014-10-25 20:51 UTC by luca.barbieri
Modified: 2015-07-27 11:35 UTC (History)
6 users (show)

Tags: ac
Is this bug a regression?: ---
Last known good build:

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Description luca.barbieri 2014-10-25 20:51:53 UTC
This is the decompiled code of BindableObject.ApplyBindings:

protected void ApplyBindings (object oldContext = null)
        BindableObject.BindablePropertyContext[] array = this.properties.ToArray ();
        for (int i = 0; i < array.Length; i++) {
                BindableObject.BindablePropertyContext bindablePropertyContext = array [i];
                BindingBase binding = bindablePropertyContext.Binding;
                if (binding != null) {
                        if (oldContext != null) {
                                binding.Unapply ();
                        binding.Apply (this.BindingContext, this, bindablePropertyContext.Property);

This is wrong, because calling binding.Unapply only when oldContext is null makes no sense.

oldContext being null has nothing to do with whether the binding was applied (you can/should be able to set bindings with null BindingContext just fine, by setting Source for instance), so binding.Apply fails with an exception complaining that the binding is being reused because binding.Unapply was not called.

You probably need to record whether bindings were applied using a private instance variable on BindableObject.

There probably other bugs in the code regarding null BindingContexts, stemming from the same misconception that it cannot be null.
Comment 1 Jason Smith [MSFT] 2015-07-16 17:44:55 UTC
Should be fixed in 1.4.4-pre1