attach more widgets to a QScrollArea

[franco.amato]

Defintely not

You are artificially manipulating the size of each child widget which is not a very good idea. Using graphics view or implementing everything as one widget derived from QAbstractScrollArea would be a much better approach.

Thank you very much.
Can you give some line the code just to start the widget derived from QAbstractScrollArea?

Best

[wysota]

I can't give you a complete 10 line sample. I can tell you it is just like any ordinary widget with exception that at each time you only see part of it and the part seen is manipulated using QAbstractScrollArea::scrollContentsBy() that you will need to implement.

[franco.amato]

I can't give you a complete 10 line sample. I can tell you it is just like any ordinary widget with exception that at each time you only see part of it and the part seen is manipulated using QAbstractScrollArea::scrollContentsBy() that you will need to implement.

Why I can not inherits from QScrollArea instead of QAbstractScrollArea?

[wysota]

You can but in my opinion this is a bad idea for the functionality you are trying to implement.

[franco.amato]

You can but in my opinion this is a bad idea for the functionality you are trying to implement.

Is a bit difficult...and I can not find a valid example

[wysota]

What is so difficult in it? As for examples, you have the code of Qt, you also have examples of classes that are derived from classes that are derived from QAbstractScrollArea (like views in Item Views).

[franco.amato]

What is so difficult in it? As for examples, you have the code of Qt, you also have examples of classes that are derived from classes that are derived from QAbstractScrollArea (like views in Item Views).

I can not find such example in my Qt 4.6.0 installation

[wysota]

I can not find such example in my Qt 4.6.0 installation

Qt source code is one big example But you may also look at the "chart" example.

[franco.amato]

Qt source code is one big example But you may also look at the "chart" example.

Thank you very much wysota, but I think what I need is simpler that it appear to be.
I wrote a routine that draw an audio graph depending on how many audio samples I would display and which is the width of the widget containing the graph.
So in case of

• resizing
• zoomIn
• zoomOut

what change (automatically resizing, or manually zooming) is the width of the widget accordingly to that I draw the correct audio wave.
So I think I don't need to go so deeply reimplementing the method you suggested to me. Maybe I'm wrong.
What do you think?

Best Regards

[wysota]

At some point there comes a time where you have to go past your current skills and examples. I think the time has come for you, especially that it seems you have over two years of experience with Qt. You either do it wrong (like you are doing now) and learn nothing or you make some effort, learn and do the thing properly.

[franco.amato]

At some point there comes a time where you have to go past your current skills and examples. I think the time has come for you, especially that it seems you have over two years of experience with Qt. You either do it wrong (like you are doing now) and learn nothing or you make some effort, learn and do the thing properly.

Already done but seems you didn't agree with my solution

[wysota]

Already done but seems you didn't agree with my solution

Your solution will fall apart once you need to add more functionality to it. Composing your GUI from already existing widgets is not the only possibility, sometimes you need to create a custom widget consisting of something more than just a paint event.

[franco.amato]

Your solution will fall apart once you need to add more functionality to it. Composing your GUI from already existing widgets is not the only possibility, sometimes you need to create a custom widget consisting of something more than just a paint event.

I started rewriting a custom widget derived from QScrollArea so:

class WaveDisplay : public QScrollArea
{
  ..code..
};

class WaveDisplay : public QScrollArea
{
  ..code..
};

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As I understood until now, QScrollArea show its scroll bars only when the child widgets are bigger than the scrollarea viewport right?
Here I have a doubt. If my widget inherits from QScrollArea, then it doesn't have a child widget as it's the child widget. So it's size will never
be bigger than the viewport. It's size will always be equal the viewport and the scroll bars will never appears of I'm saying something foo?

I hope someone can clarify this to me.

Best

[wysota]

Deriving from QScrollArea doesn't make sense because eventually you will do the same what you did before. You have to use QAbstractScrollArea and abandon your wave widget class and move its code inside your new class. The point of deriving from QAbstractScrollArea is that you can provide zooming and panning facilities without the need to manipulate widget sizes and layouts. If that's too complicated for you then derive from QScrollArea like you did before but don't use a layout for your scrolled widget and instead position the widgets manually upon every need to do so.

[franco.amato]

Deriving from QScrollArea doesn't make sense because eventually you will do the same what you did before. You have to use QAbstractScrollArea and abandon your wave widget class and move its code inside your new class. The point of deriving from QAbstractScrollArea is that you can provide zooming and panning facilities without the need to manipulate widget sizes and layouts. If that's too complicated for you then derive from QScrollArea like you did before but don't use a layout for your scrolled widget and instead position the widgets manually upon every need to do so.

Hi before I didn't derived from QScrollArea...is what I'm trying to do now. Please can you help me with a little example of zooming in this case?
My experience is too little at the moment. I'll really appreciate it.

Best Regards

[wysota]

Hi before I didn't derived from QScrollArea...is what I'm trying to do now.

Deriving or using.. what's the difference?

Please can you help me with a little example of zooming in this case?

No, because in my opinion this is a wrong approach. If you insist on doing this, use QWidget::setGeometry() to change the geometry of child widgets.

[franco.amato]

Deriving or using.. what's the difference?

No difference

No, because in my opinion this is a wrong approach. If you insist on doing this, use QWidget::setGeometry() to change the geometry of child widgets.

I would use a better approach, but I'm sure you understood that I'm unable to do.
I have a very poor experience in writing gui and how can I improve it if I don't get help? Sometime a very basic example is very usefull starting point. I did't ask to you to provide a complete software

[wysota]

I have a very poor experience in writing gui and how can I improve it if I don't get help?

Come on, man... Registration date - Nov 2007, 163 posts and no experience?

Sometime a very basic example is very usefull starting point.

Always relying on mimicing existing code doesn't lead to extending your skills. What example would you want me to give you? Something like this?

QWidget *w = new QWidget(viewport());
w->setGeometry(20, 20, 200, 100);

QWidget *w = new QWidget(viewport());
w->setGeometry(20, 20, 200, 100);

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[franco.amato]

Come on, man... Registration date - Nov 2007, 163 posts and no experience?

In my work only write very basic gui...until now
That's my experience.

Always relying on mimicing existing code doesn't lead to extending your skills. What example would you want me to give you? Something like this?

QWidget *w = new QWidget(viewport());
w->setGeometry(20, 20, 200, 100);

QWidget *w = new QWidget(viewport());
w->setGeometry(20, 20, 200, 100);

To copy to clipboard, switch view to plain text mode 

What I didn't understand is (with an object inherited from QScrollArea)
for example MyWidget : QScrollArea the view port is always = to the width right or not? This is my doubt. If so how scrollarea manage scroll bars?

[wysota]

Viewport is always smaller than the view.

If so how scrollarea manage scroll bars?

It reimplements QAbstractScrollArea::scrollContentsBy().