How do I changle the picture displayed by a picturebox from outside the form

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Ordinarily, when I want to change the image displayed by a pictureBox from within a Windows form, I fire an event like this:

C++

private: System::Void PicBoxMonton1_DoubleClick(System::Object^  sender, System::EventArgs^  e)
{
    if (this->PicBoxMonton1->Image != Image::FromFile(Glo::m_Empty))
    {
        this->PicBoxMonton1->Image = Image::FromFile(Glo::m_Empty);
        ....
        ....
    }
}

This syntax (this->PicBoxMonton1->Image) doesn't work when I try to execute the if statement from within a function written in a separate .cpp file where all my function are.
I am a beginner.
Which parameters do I need to pass to the function?
How do I change the instruction within the if statement?

What I have tried:

Everything within my limited experience. And I haven't found a single example to illustrate me.

Posted 4-Mar-17 5:18am

Terence Moore

Updated 4-Mar-17 6:45am

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Richard MacCutchan 4-Mar-17 11:25am

That is because the this keyword refers to the enclosing class. In this case the Form that contains the event handler. You need to get a reference to the Form in order to call that method.

Terence Moore 4-Mar-17 19:06pm

Exactly. That has been my understanding all along. But how do I construct a reference to the Form? I have tried things like namespace::MyForm->pictureBox->Image but no luck. Thank you.

Richard MacCutchan 5-Mar-17 2:33am

You don't construct it. When you create the form in the first place you need to save the reference somewhere.

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KarstenK · Answer 1 · 2017-03-04T06:45:00

Solution 1

To solve the problem you should declare a public function which you call from the outside. For that you need a valid pointer to your form class instance.

Another issue is, that the call must be in the main thread of your app. Only if it is not in the main thread take a look at this answers at stackoverflow.

Posted 4-Mar-17 6:45am

KarstenK

Comments

Terence Moore 4-Mar-17 19:00pm

Thanks for the input. The function is already declared public.
How do I construct a valid pointer to my form class instance?.
THANK YOU.