# Bug? Apvts doesn't fully sync missing parameters on assignment

**URL:** <https://forum.juce.com/t/bug-apvts-doesnt-fully-sync-missing-parameters-on-assignment/51509>\
**Category:** General JUCE discussion\
**Created:** [May 18, 2022, 3:13pm UTC](https://forum.juce.com/t/bug-apvts-doesnt-fully-sync-missing-parameters-on-assignment/51509 "2022-05-18T15:13:36Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![sudara](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/sudara/32/8071_2.png) [@sudara](https://forum.juce.com/u/sudara)\
**Post date:** [May 18, 2022, 3:13pm UTC](https://forum.juce.com/t/bug-apvts-doesnt-fully-sync-missing-parameters-on-assignment/51509/1 "2022-05-18T15:13:36Z")

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Hi there,

Let’s say I have an apvts with two parameters added:

```auto
std::make_unique<juce::AudioParameterFloat> (ParameterID("gain", 1), "Gain", 0.0f, 1.0f, 0.5f),
std::make_unique<juce::AudioParameterBool> (ParameterID("invertPhase", 1), "Invert Phase", false)

```

If I assign a new state to the apvts (such as in `setStateInformation`), my expectation was that the apvts synchronizes with parameters and adds any PARAM children to the ValueTree that might be missing.

It seems that the children are added, but with no `value` property. So the apvts ValueTree ends up in a surprising “half existing” state.

To reproduce:

```auto
    ValueTree mockIncomingState { "incoming" };
    mockIncomingState.copyPropertiesAndChildrenFrom(parameters.state, nullptr);
    mockIncomingState.removeChild(1, nullptr); // remove the boolean "invert phase" parameter
    parameters.state = mockIncomingState; // copy to apvts
    jassert(parameters.state.getChild(1).hasProperty("id"));
    jassert(parameters.state.getChild(1).hasProperty("value"));

```

An assertion happens on the last line. Is this a bug, or is there an incantation I’m missing to get the `value` to populate?

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<div class="post-metadata">

**Author:** ![sudara](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/sudara/32/8071_2.png) [@sudara](https://forum.juce.com/u/sudara)\
**Post date:** [May 19, 2022, 11:58am UTC](https://forum.juce.com/t/bug-apvts-doesnt-fully-sync-missing-parameters-on-assignment/51509/2 "2022-05-19T11:58:05Z")

</div>

Looking at the parameter reconstruction after assignment, it seems like [only the id is set, not the value.](https://github.com/juce-framework/JUCE/blob/master/modules/juce_audio_processors/utilities/juce_AudioProcessorValueTreeState.cpp#L437-L442)

`flushParameterValuesToValueTree` is then called, and I would have expected `value` to be populated, but [this conditional returns false](https://github.com/juce-framework/JUCE/blob/master/modules/juce_audio_processors/utilities/juce_AudioProcessorValueTreeState.cpp#L133).

In my own code, I worked around the issue by avoiding apvts assignment and instead manually iterating over the existing PARAM children, using it as an allow list / source of “truth.”

That way, if the incoming state is missing PARAM children (for example, an older version of state before a new parameter was added), there’s no indeterminate “half” state.