How to delete a row of a QGridLayout

JonB

int row = this->rowCount();
...
while ((child = this->takeAt(row)) != nullptr) {

Don't rows (for takeAt(row)) count from 0 to rowCount() - 1? So your code will do nothing (docs: "If there is no such item, the function must do nothing and return 0."), and never enter the while loop?

As for the commented-out attempt:

//        for (int i(0); i > 4 ; ++i){
//            this->itemAtPosition(row,i)->widget()->hide();
//            delete this->itemAtPosition(row,i);
//        }

~~won't do what you intend because you delete at i and then increment i, not taking into account that you have done a deletion which squeezes other items down (i.e. it deletes every other item)?~~ That apart, i starts at 0 and your loop while condition is i > 4, so it will never enter the loop anyway.

In both these cases you would find out what is/is not happening if you put some kind of trace/debug statements into your code.

Maxime0601

@jonb
For the part with the takeAt(row), I think that I haven't really understand the method. However, it works but it delete more than I hoped.

For the other part, the i > 4 is just a mistake when I edited my code but with i < 4 the program crashs. If I understand well your explain I just have to delete the first element and after it will delete others under it?

Pl45m4

@maxime0601 said in How to delete a row of a QGridLayout:

I edited my code but with i < 4 the program crashs

i < 4 only works if you have 4 items in your Grid, otherwise there is no column 3.

You have to replace the 4 with the number of your current cols.

Maxime0601

@pl45m4

    int row = this->rowCount();
    int col = this->columnCount();
    if (row > 6)
    {
        for (int i(0); i < col ; ++i){
            this->itemAtPosition(row,i)->widget()->hide();
            delete this->itemAtPosition(row,i);
        }
    }
}

It also crashs like this.

JonB

@maxime0601
I already said/suggested

int row = this->rowCount();
...
this->itemAtPosition(row,i)->widget()->hide();

Don't rows count from 0 to this->rowCount() - 1? So your row exceeds the number of rows, hence crashes? Test what this->itemAtPosition(row, 0) returns, or crashes?

Then when you have this right, I don't think you should directly delete an item (which is still owned by the grid layout), shouldn't you do some kind of:

delete this->takeAt(?)

Pl45m4

@maxime0601

Try to remove the widget from your layout (instead of hiding it).

Maxime0601

@jonb It continues to crash

@Pl45m4 I also tried with

this->removeWidget(itemAtPosition(row,0)->widget()->hide();

and it crashes too.

jsulm

@maxime0601 said in How to delete a row of a QGridLayout:

It continues to crash

then please use the debugger to see what exactly happens and where...

JonB

@maxime0601

@jonb It continues to crash

@Pl45m4 I also tried with

this->removeWidget(itemAtPosition(row,0)->widget()->hide();

and it crashes too.

Last time of saying: what does itemAtPosition(row,0) return/do, given your value of row?? How difficult is it to test that?

Maxime0601

@jsulm I have a signal of segmentation fault. It confirms that I try to use an outside element of my grid

jsulm

@maxime0601 said in How to delete a row of a QGridLayout:

I try to use an outside element of my grid

Well, then fix that. And I know that it is crashing and my suggestion to use debugger is still valid: you will see where exactly it is crashing and what the values of variables at that time.
Did you read what @JonB wrote?

Maxime0601

@jonb I'm sorry if I don't understand what you mean but when I tried itemAtPosition(row,0) it crashes.
@jsulm the problem is at column 4 and row 7 and it is the position of one of the element that I want to delete.

Oh I tried with row - 1 and it seems works

JonB

@maxime0601

@jonb I'm sorry if I don't understand what you mean but when I tried itemAtPosition(row,0) it crashes.

Which is why I said your program crashes all the time! You are not understanding that rows are numbered starting from 0 and going to rowCount() - 1, not to rowCount(). That's how most arrays etc. are numbered in C/C++. I don't know how to explain any better, you really need to understand this fundamental, rather than banging stuff in without understanding:

Oh I tried with row - 1 and it seems works

You really need to understand why that it is, rather than "seems to work".

Maxime0601

int row = this->rowCount();
int col = this->columnCount();
if (row > 6)
{
   for (int i(0); i < col ; ++i)
   {
         this->itemAtPosition(row - 1,i)->widget()->hide();
         delete this->takeAt(row - 1);
   }
}

So, when I used this code, the last row disappeared as I want but the disposition of the others elements in the grid changes.

@JonB yes I knew this for vector but I totally forgot it. I'm sorry for that.

JonB

@maxime0601
I'm sorry but it's more complex than you are expecting. You really need to read https://stackoverflow.com/questions/5395266/removing-widgets-from-qgridlayout. I know it looks a lot more involved than what you are trying, but there you are....

Maxime0601

@jonb Thanks a lot, I've searched but I don't found similar topic. I think that I can succeed with this.
Thanks a lot everyone for your help