[Interest] Qt5: Obtain current layout size

Bo Thorsen bo at fioniasoftware.dk
Tue Jul 24 10:08:13 CEST 2012

Den 23-07-2012 15:41, Stephen Chu skrev:
> On 7/23/12 4:52 AM, Bo Thorsen wrote:
>> Den 22-07-2012 21:49, Stephen Chu skrev:
>>> On 7/22/12 6:30 AM, Bo Thorsen wrote:
>>>> Den 21-07-2012 18:27, Stephen Chu skrev:
>>>>> I am working on a dynamically generated form. One thing I'd like to do
>>>>> is to reflow the layout into multi-column when the widgets fill the
>>>>> preset window height.
>>>>> I need to find out what the current layout height is before I add the
>>>>> new widget. The problem is, layout geometry is always 0x0 before the
>>>>> window is shown. And if I show the window before adding the widgets,
>>>>> not
>>>>> only does the window flickers badly, it also doesn't auto-position
>>>>> correctly. What's worse, the geometry reported is still 0x0.
>>>>> So how do I get the correct layout or parent widget size before
>>>>> showing
>>>>> the widget/window? Thanks.
>>>> You can't use size or geometry because they are properties of what is
>>>> actually shown.
>>>> For your case, you should use the minimum sizes instead. Those
>>>> should be
>>>> available to you.
>>> Thanks. That works. Do you happen to know how I can get the size of a
>>> window maximized without first maximize it?
>> You can't do that.
>> The real fix for what you are trying to do here is to write your own
>> layout manager class. You should subclass QLayout and implement the
>> layouting yourself. It's the only way (I think) that truly does what you
>> want to achieve without using a bunch of bad hacks along the way.
> I wouldn't say it's a hack. I am arranging the layout dynamically by
> considering how much the window is allowed to grow.

What you're trying to do isn't a hack, of course. What you end up having 
to do to implement it will be. Your problem with the full screen shows this.

> And even if I go custom layout route, I still need to know where I need
> to place the new widget so I don't grow the window out of the screen,
> right?

The layout manager is asked the minimum size of the widget, which for 
you is impossible to answer. This is already an indication why you have 
problems here.

In case you want to discuss if this is possible or not: minimumSize 
gives a QSize back. In your case, the minimum height is actually the 
height of one row. But for any number of rows, the minimum width changes.

There is, however, a function called heightForWidth or widthForHeight - 
I don't remember which way they chose. This might actually be exactly 
what you are looking for. Try experimenting with that.

Anyway, once the size of the window is chosen, the layout manager is 
asked to place the widgets inside the parent. At this point, the layout 
knows what size the container will have, so it can place the widgets 

Bo Thorsen,
Fionia Software.


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