# Callback from Array\<PropertyComponent\*\>

**URL:** <https://forum.juce.com/t/callback-from-array-propertycomponent/25311>\
**Category:** General JUCE discussion\
**Created:** [November 26, 2017, 8:04am UTC](https://forum.juce.com/t/callback-from-array-propertycomponent/25311 "2017-11-26T08:04:36Z")\
**Posts on this page:** 9\
**Page:** 1

<div class="post-metadata">

**Author:** ![Rodolphe](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/rodolphe/32/3345_2.png) [@Rodolphe](https://forum.juce.com/u/Rodolphe)\
**Post date:** [November 26, 2017, 8:04am UTC](https://forum.juce.com/t/callback-from-array-propertycomponent/25311/1 "2017-11-26T08:04:37Z")

</div>

Hello,  
I liked the PropertiesDemo example in the Juce Demo, but stuck with the choice made of adding pointers of class DemoSliderPropertyComponent to an array of PropertyComponent\*.  
Could someone be kind enough to illustrate the way we can get callback from the sliders in this specific example ?

---

<div class="post-metadata">

**Author:** ![ed95](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/ed95/32/7635_2.png) [@ed95](https://forum.juce.com/u/ed95)\
**Post date:** [November 26, 2017, 4:54pm UTC](https://forum.juce.com/t/callback-from-array-propertycomponent/25311/2 "2017-11-26T16:54:24Z")

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The `DemoSliderPropertyComponent` class in the JUCE Demo inherits from `SliderPropertyComponent` so you can access its `protected` `Slider` member and attach a listener to it. You’ll need to inherit from `Slider::Listener` and then call `slider.addListener (this)` in the constructor. Then implement the listener’s `sliderValueChanged()` method, which will be called whenever the `Slider` value changes.

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<div class="post-metadata">

**Author:** ![Rodolphe](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/rodolphe/32/3345_2.png) [@Rodolphe](https://forum.juce.com/u/Rodolphe)\
**Post date:** [November 26, 2017, 6:10pm UTC](https://forum.juce.com/t/callback-from-array-propertycomponent/25311/3 "2017-11-26T18:10:00Z")

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This is clear for me. What is less clear is how to get it working in the context of the PropertiesDemo example. I would really need that for a better understanding.  
In the example, demoSliderComponents are added to an array of PropertyComponent. When I create a demoSliderComponent, I can’t do slider.addListener with this newly added component.  
Let’s say I do the following:  
Considering displayLimits is defined like this, in order for being able to be added to the main propertyPanel with the function addSection() :

```
	Array<PropertyComponent*> displayLimits;

```

Then when I write the following code:

```
		DemoSliderPropertyComponent* s = new DemoSliderPropertyComponent ("Something rich and strange");
	displayLimits.add (s);
	s->addListener(this);

```

(‘this’ implementing Slider::Listener),  
I get: “No member named addListener in DemoSliderPropertyComponent”

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<div class="post-metadata">

**Author:** ![ed95](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/ed95/32/7635_2.png) [@ed95](https://forum.juce.com/u/ed95)\
**Post date:** [November 27, 2017, 8:52am UTC](https://forum.juce.com/t/callback-from-array-propertycomponent/25311/4 "2017-11-27T08:52:01Z")

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Well no that won’t work as `DemoSliderPropertyComponent` isn’t a `Slider`, it just contains one as a child component. If you wanted to do something like your example, you’d need to expose its `Slider` as a public member or have getter method then you could do:

```
s->slider.addListener (this);

```

What are you trying to achieve though? You’ll probably be better off just using a `SliderPropertyComponent` to control a `Value` object that you can listen to. So you’d have some member variables like this:

```auto
OwnedArray<PropertyComponent> propertyComponents;
Value valueToControl;

```

and then in your constructor:

```auto
valueToControl.addListener (this);
...
propertyComponents.add (new SliderPropertyComponent (valueToControl, "SliderProperty", 0.0, 1.0, 0.1));

```

Now if your parent class inherits from `Value::Listener` and implements its `valueChanged()` method you will get a callback whenever the user moves the `Slider` and changes its underlying `Value`.

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<div class="post-metadata">

**Author:** ![Rodolphe](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/rodolphe/32/3345_2.png) [@Rodolphe](https://forum.juce.com/u/Rodolphe)\
**Post date:** [November 27, 2017, 9:34pm UTC](https://forum.juce.com/t/callback-from-array-propertycomponent/25311/5 "2017-11-27T21:34:25Z")

</div>

> [@ed95](#):
>
> new SliderPropertyComponent

Thanks, that looks nice. However I tried the following and could not monitor any change from the Slider, could you tell where I got wrong ?:

class SettingsGUI : public Component, public Value::Listener, public Slider::Listener  
{

```
public:
SettingsGUI()
{
	PropertyPanel* panel = new PropertyPanel ("Project Settings");
	valueToControl.addListener(this);
	someSliders.add (new SliderPropertyComponent (valueToControl, "valueOfSomeKind", 0.0, 1.0, 0.1));
	panel->addSection("Special", someSliders, true);
}
void valueChanged (Value &value) override
{
	DBG(" valchgd: " << value.toString());
}
private:
Array<PropertyComponent*> someSliders;

```

};

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<div class="post-metadata">

**Author:** ![ed95](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/ed95/32/7635_2.png) [@ed95](https://forum.juce.com/u/ed95)\
**Post date:** [November 28, 2017, 9:09am UTC](https://forum.juce.com/t/callback-from-array-propertycomponent/25311/6 "2017-11-28T09:09:15Z")

</div>

Here is a really minimal working example:

```auto
//==============================================================================
class MainContentComponent : public Component,
                                  private Value::Listener
{
public:
    //==============================================================================
    MainContentComponent()
    {
        valueToControl.addListener (this);
        
        sliderProps.add (new SliderPropertyComponent (valueToControl, "Slider", 0.0, 1.0, 0.01));
        propPanel.addSection ("Sliders", sliderProps);
        
        addAndMakeVisible (propPanel);
        
        setSize (600, 400);
    }
    
    ~MainContentComponent() {}

    void paint (Graphics& g) override
    {
        g.fillAll (getLookAndFeel().findColour (ResizableWindow::backgroundColourId));
    }
    
    void resized() override
    {
        propPanel.setBounds (getLocalBounds().reduced (5));
    }

private:
    void valueChanged (Value& v) override
    {
        DBG ("Value changed");
    }
    
    Value valueToControl;
    Array<PropertyComponent*> sliderProps;
    PropertyPanel propPanel;
    
    //==============================================================================
    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (MainContentComponent)
};

```

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<div class="post-metadata">

**Author:** ![Rodolphe](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/rodolphe/32/3345_2.png) [@Rodolphe](https://forum.juce.com/u/Rodolphe)\
**Post date:** [November 28, 2017, 5:24pm UTC](https://forum.juce.com/t/callback-from-array-propertycomponent/25311/7 "2017-11-28T17:24:32Z")

</div>

Well, thanks and sorry for my last complaint: I don’t why, but my own code was working, in fact.  
While we are getting to the core of the question: how do I distinguish in this example, which slider has issued the value (if I add more sliders) ?

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<div class="post-metadata">

**Author:** ![ed95](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/ed95/32/7635_2.png) [@ed95](https://forum.juce.com/u/ed95)\
**Post date:** [November 28, 2017, 5:40pm UTC](https://forum.juce.com/t/callback-from-array-propertycomponent/25311/8 "2017-11-28T17:40:56Z")

</div>

The `valueChanged()` callback is called with a reference to the `Value` that has been modified as its argument, so you can compare this to your `Value` members to determine which has changed.

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<div class="post-metadata">

**Author:** ![Rodolphe](https://sea2.discourse-cdn.com/flex026/user_avatar/forum.juce.com/rodolphe/32/3345_2.png) [@Rodolphe](https://forum.juce.com/u/Rodolphe)\
**Post date:** [November 28, 2017, 7:57pm UTC](https://forum.juce.com/t/callback-from-array-propertycomponent/25311/9 "2017-11-28T19:57:16Z")

</div>

Great, that worked!  
I am not used to Values, so did’nt know the easiest way.  
Thanks