当给定 100k 项时，QListView 需要很长时间才能更新 [英] QListView takes too long to update when given 100k items

问题描述

我在读取文件时遇到问题，具体是我想制作一个小词典.在我需要阅读的文件中有这样的内容:

I have a problem with reading file, specific is I want to make a small dictionary. In file which I need to read has content like this:

a   Ph  P6
a   snsr    CA
a b c   fb  Dj
a b c - book    i+  BS
A except B gate oOPa    y
a font  kQ  BU
[....]

它大约有 109.000 行，文件只有大约 2MB.在我的 QT 应用程序中，我这样编码以读取项目并将其添加到 QListWidget:

It has about 109.000 lines, and file just has size about 2MB. In my QT app, I coded like this to read and add items to QListWidget:

QString sWord;
QFile inFile("C:\EV\ev.index");

inFile.open(QIODevice::ReadOnly|QIODevice::Text);
QTextStream in(&inFile);
while(!in.atEnd())
{
     sWord = in.readLine();
     myListWidget->addItem(sWord); //myListWidget is a QListWidget
}

但是它读得太长了！起初我认为原因是我的应用程序逐行读取，所以我再次这样编码:

But it reads too long! At first I think reason is my app reads line by line, so I coded its again like this:

QString data;
QStringList listWord;
QFile inFile("C:\EV\ev.index");


inFile.open(QIODevice::ReadOnly|QIODevice::Text);
QTextStream in(&inFile);
data.append(in.readAll());
listWord.append(data.split('
'));
myListWidget->addItems(listWord);
inFile.close();

它运行得更快！(自应用启动后大约 5 秒)，仍然很长，我希望它读得更快.我必须做什么?

It works faster!(about 5 seconds since app launched), still long, I want it to read faster. What I have to do?

推荐答案

1. 列表小部件的布局时间太长.将列表小部件的 uniformItemSizes 属性设置为 true.这避免了昂贵的布局操作.另一种方法是将 layoutMode 属性设置为 QListView::Batched.这样可以避免一次昂贵地布置所有项目.

1. The list widget's layout takes too long. Set your list widget's uniformItemSizes property to true. This avoids expensive layout operations. Another way would be to set the layoutMode property to QListView::Batched. This avoids having to expensively lay out all of the items at once.

如果QListView 开销较低，请不要使用QListWidget.

Don't use a QListWidget if a lower overhead QListView would do.

应该批量添加大量元素，即不要将元素一个一个地插入模型中.在原子操作中插入来自每个批次的元素，该操作仅发出一次 rowsInserted 或 columnsInserted 信号.

Additions of large numbers of elements should be batched, i.e. do not insert the elements into the model one-by-one. Insert elements from each batch in an atomic operation that emits the rowsInserted or columnsInserted signal only once.

您不得在 GUI 线程中加载任何文件.这是许多应用程序中糟糕的用户体验的根源，必须非常轻蔑地劝阻.不要这样做.

You must not do any file loading in the GUI thread. This is a source of bad user experience in a lot of applications and must be discouraged with a heapful of scorn. Don't do it.

下面是一个考虑到所有这些的最小示例.

Below is a minimal example that takes all of those into account.

// https://github.com/KubaO/stackoverflown/tree/master/questions/filemodel-18548048
#include <QtWidgets>
#include <QtConcurrent>

void makeLines(QBuffer &buf, int count = 1000000) {
   buf.open(QIODevice::WriteOnly | QIODevice::Text);
   char line[16];
   for (int i = 0; i < count; ++i) {
      int n = qsnprintf(line, sizeof(line), "Item %d
", i);
      buf.write(line, n);
   }
   buf.close();
}

struct StringListSource : QObject {
   Q_SIGNAL void signal(const QStringList &);
   void operator()(const QStringList &data) { emit signal(data); }
   Q_OBJECT
};

int main(int argc, char *argv[]) {
   QApplication app(argc, argv);
   QListView view;
   QStringListModel model;
   StringListSource signal;
   QObject::connect(&signal, &StringListSource::signal, &model, &QStringListModel::setStringList);
   QtConcurrent::run([&signal]{
      QBuffer file;
      signal({"Generating Data..."});
      makeLines(file);
      signal({"Loading Data..."});
      QStringList lines;
      if (file.open(QIODevice::ReadOnly | QIODevice::Text))
         while (!file.atEnd())
            lines.append(QString::fromLatin1(file.readLine()));
      file.close();
      signal(lines);
   });
   view.setModel(&model);
   view.setUniformItemSizes(true);
   view.show();
   return app.exec();
}
#include "main.moc"

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