Help wanted: paintEvent is only called once in a series of datachanged event

[farley]

Hello, everyone:

I want to achieve a continuous text appending effect in the window, like this.

but the window's text only refreshes during the last text update operation, omitting the intermediate process. I debugged the code and found that the paintEvent is only called once in a series of dataChanged events. I would like to know how to modify my code to achieve this functionality.

Here is a link to my github issue

Below is my code:

#include <QListView>
#include <QStandardItemModel>
#include "ichatitemdelegate.h"
#include "ichatitemmodel.h"

class IChatList: public QListView
{
public:
    using QListView::QListView;
public:
    explicit IChatList(QWidget *parent = nullptr)
        : QListView(parent)
    {
        setModel(new IChatItemModel(this));
        setItemDelegate(new IChatItemDelegate(this));
    }
    void paintEvent(QPaintEvent *e) override{
        QListView::paintEvent(e);
        qDebug() << "void paintEvent(QPaintEvent *e)";
    }
public:
    void appendText(QString text) {

        auto model = qobject_cast<QStandardItemModel*>(this->model());
        if (!model) {
            qDebug() << "Chat list model is null.";
            return;
        }

        QStandardItem *lastItem = nullptr;
        int rowCount = model->rowCount();
        if (rowCount > 0) {
            QModelIndex lastIndex = model->index(rowCount - 1, 0);
            lastItem = model->itemFromIndex(lastIndex);
        }
        if (!lastItem) {
            // 如果没有最后一行item，创建一个新的item并添加到模型中
            lastItem = new QStandardItem();
            model->appendRow(lastItem);
        }
        // 获取最后一个item的数据，并更新 message 字段
        QVariant itemData = lastItem->data(Qt::DisplayRole);
        QVariantMap chatData1 = itemData.toMap(); // 显式转换为 QVariantMap
        chatData1["message"] = chatData1["message"].toString() + " " + text;
        lastItem->setData(chatData1, Qt::DisplayRole);
        qDebug() << "appendText:" << text;
        // 发出数据变化信号，通知视图刷新
        QModelIndex topLeft = model->index(0, 0);
        QModelIndex bottomRight = model->index(rowCount - 1, 0);
        emit model->dataChanged(topLeft, bottomRight);
        repaint();
    }
public:
};

Waiting for your help.

[SGaist]

Hi and welcome to devnet,

One possible solution is to buffer the updates and update the content of the model on a regular interval using for example a QTimer.

[MasterBLB]

Looks like problem xy...
What is your ultimate goal to achieve? Do you want the list view to be displayed once new line is inserted?

Meanwhile, some hints:

1. [MOD EDIT] redacted. OP advised not to use Chinese characters in sources, but in a very unfriendly way
2. appendText() method is absolutely redundant and ill-placed, as adding new stuff to the model is not responsibility of view class.
3. Relating to point 2. you don't even have to reimplement anything, as there is void QStandardItemModel::appendRow(QStandardItem *item)

I think just by using that proper appendRow() method your sync issues will be gone, as inside there are proper calls to emit dataChanged(), update(), beginInsertRows() etc.

[sierdzio]

@MasterBLB while I also recommend sticking to English in all source code, using wide UTF characters has no influence on this code whatsoever. Firstly, they are used in comments only, and secondly: both Qt and all modern compilers support UTF just fine.

[MasterBLB]

@sierdzio Sorry, I didn't mean to be unfriendly. It is just that would these comments were in English it might help to understand initial idea of the thread author, and figure out some way to help him, or her.

[farley]

@MasterBLB Hello, thanks for your reply.
My ultimate goal is to display byte stream from netport instantly in listview.
Luckily, my problem is solved by replace signal QNetworkAccessManager::finished to QNetworkReply::readyRead in my code.

Additionally,

1. I also think it's preferable to use English throughout all source code for better communication with others in a friendly manner.But sometimes also tend to be lazy.
2. So, I learned adding new stuff to the model is not responsibility of view class. I'll directly write this funtion in mainwindow.

[farley]

@SGaist Thank you for your suggestion, problemed is solved althought without QTimer. : )