push button is able to recieve output only once!!!

[Choti]

Hello everyone,


I have problem with the output on QListWidget. I am using 3 push buttons, READ, EDIT and CHANGE. In READ push button I have function for getting the values from the server, in EDIT button I using it to edit the values I receive form server. Finally after editing the values by using the CHNAGE button I am sending the vales back to server.

Now I am problem is I am able to get the values only once, when I try to push the buttons READ and CHANGE they are returning the errors. My idea is to get the values whenever I push the READ and CHANGE buttons. I am not understanding whetherits the problem with the push button or with my functions.

Can anyone please help me with this issue?


Thank you.

[Lesiok]

What do You mean "buttons are returning the error" ?

[Choti]

I mean when I push th ebutton for the first time I able to recieve the data and when I do it again then there is no data recieving. I am getting error message from server.

[Lesiok]

It has nothing to do with the button. Probably the first download data from the server is not completed correctly. We do not know what a server is, as it retrieves the data and so on. I think that a problem is in the procedure activated when the button is pressed.

[Choti]

Thank Mr.Lesiok... the problem was solved ... its in the function not with the push button....

Can you please also help me with error handling function for push button?.

I mean when I click on READ button I get the data and the using EDIT button I should be able to edit the data. But when I click the EDIT button with out clicking the data the window is crashing down. So I wanted nmake something like when we push the EDIT button with out getting any data or without clicking on the data it should return a message saying "Pleae click on the data to edit" or "No data is available"....

I want my window not to get closed when we click on EDIT button directly.. can you suggest some ideas how to get over this problem?


Thank you.

[anda_skoa]

Sounds like the slot you have connected to the edit button tries to access something that is not initialized or not existant.
Fix that and the problem should be gone.

Cheers,
_

[Choti]

void MainWindow:n_pushButton_2_clicked()
{

QListWidgetItem *item = ui->valueWidget->currentItem();
item->setFlags(item->flags()|Qt :: ItemIsEditable);
ui->valueWidget->editItem(item);

}


this is my code which I have implemented for EDIT button. In valueWidget I have the values which I am going to edit. But when I click on EDIT button directly the window is crashing down.

[Lesiok]

Maybe ui->valueWidget->currentItem() returns NULL pointer. Use debugger to locate a problem.

[Choti]

Thank you Mr.Lesiok,


Do you think I can use another function instead of currentItem(); ??

[Lesiok]

No, I think you need to find the cause of the problem and not invent its workaround.

[Choti]

Yes ui->valuewidget->currentItem() ; is returning null pointer....

[anda_skoa]

Which means the cause of the problem is calling methods on a null pointer.

If you can find a way to check the value of the pointer you could change the code to only use the pointer if it is valid.

As a next step, it might be possible to get notified when the current item changes and apply the same check to determine a good value for the EDIT button's "enabled" property.

Cheers,
_

[Choti]

I could not find the solution

[anda_skoa]

The language feature you are looking for is called "if".
It allows to test a logical condition and then execute code depending on whether the expression evalutes to "true" or "false".

if (condition) {
    // code executed when the condition is true
} else {
    // code executed when the condition is false
}

if (condition) {
    // code executed when the condition is true
} else {
    // code executed when the condition is false
}

To copy to clipboard, switch view to plain text mode 

The "else" case is optional.

In your case you can either check for the pointer being null and the code to execute being "return" or you can check for not being null and executing the code that uses the pointer.

Cheers,
_

P.S.: I would strongly recommend to work through a tutorial on C++ basics before continuing.