带有QCompleter的QLineEdit在文本为空时不会显示QCompleter的弹出菜单

Question

我有一个QLineEdit，它与一个QCompleter对象相关联。如果用户输入至少一个字符，则会显示来自QCompleter的弹出菜单，但是当用户删除最后一个字符（从而使字段为空）时，弹出菜单会消失。有没有办法使其即使在QLineEdit的文本为空时也显示？

- Andrea Bergia

Answer 1

你可以使用QCompleter::complete槽强制显示自动完成弹出窗口，一旦你的行编辑文本被清除。

lineEdit->completer()->complete();

以下是如何实现的：

• 为您的行编辑器(lineedit)定义textChanged槽(slot);
• 覆盖窗口(window)的customEvent方法;
• 在textChanged槽中，每当lineedit的文本为零时，向窗口发送用户事件(user event);
• 在customEvent方法中，每当收到用户事件(user event)时，显示自动完成器(completer)。

以下是一个示例:

mainwindow.h:

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

protected:
    void customEvent(QEvent * event);

private:
    Ui::MainWindow *ui;

private slots:
    void on_lineEdit_textChanged(QString );
};

mainwindow.cpp：

class CompleteEvent : public QEvent
{
public:
    CompleteEvent(QLineEdit *lineEdit) : QEvent(QEvent::User), m_lineEdit(lineEdit) { }

    void complete()
    {
        m_lineEdit->completer()->complete();
    }

private:
    QLineEdit *m_lineEdit;
};

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    QStringList wordList;
    wordList << "one" << "two" << "three" << "four";

    QLineEdit *lineEdit = new QLineEdit(this);
    lineEdit->setGeometry(20, 20, 200, 30);
    connect(lineEdit, SIGNAL(textChanged(QString)), SLOT(on_lineEdit_textChanged(QString )));

    QCompleter *completer = new QCompleter(wordList, this);
    completer->setCaseSensitivity(Qt::CaseInsensitive);
    completer->setCompletionMode(QCompleter::UnfilteredPopupCompletion);
    lineEdit->setCompleter(completer);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::customEvent(QEvent * event)
{
    QMainWindow::customEvent(event);
    if (event->type()==QEvent::User)
        ((CompleteEvent*)event)->complete();
}

void MainWindow::on_lineEdit_textChanged(QString text)
{
    if (text.length()==0)
        QApplication::postEvent(this, new CompleteEvent((QLineEdit*)sender()));
}

希望这可以帮到你，祝好。

- serge_gubenko

---

非常好用，谢谢！我之前一直尝试使用 QTimer::singleShot 做类似的事情，但出了些问题。 - Andrea Bergia

Answer 2

这是基于serge_gubenko答案的解决方案。该类使用QStringListModel，但可以轻松替换为任何其他模型。

Completer_line_edit.h

#include <QLineEdit>
#include <QStringListModel>
#include <QTimer>

/*! Line edit widget with auto completion based on QStringListModel.
  Modified behaviour: completion list will appear even when contents of
  line edit is empty. Full list of options will be showed when line edit
  has focus and is empty.
  */
class Completer_line_edit : public QLineEdit {
  Q_OBJECT
public:
  explicit Completer_line_edit(QWidget *parent = 0);

  //! Set list of options used for copmletion.
  inline void set_list(QStringList list) { model.setStringList(list); }

private:
  QStringListModel model;
  void focusInEvent(QFocusEvent *e);
  void customEvent(QEvent* e);
  QTimer timer;

private slots:
  void slot_text_edited();
  void slot_call_popup();

};

Completer_line_edit.cpp

#include "Completer_line_edit.h"
#include <QCompleter>
#include <QEvent>
#include <QApplication>

Completer_line_edit::Completer_line_edit(QWidget *parent) :
  QLineEdit(parent)
{
  setCompleter(new QCompleter());
  completer()->setModel(&model);
  completer()->setCompletionMode(QCompleter::PopupCompletion);
  completer()->setCaseSensitivity(Qt::CaseInsensitive);
  connect(this, SIGNAL(textEdited(QString)), this, SLOT(slot_text_edited()));
}

void Completer_line_edit::focusInEvent(QFocusEvent *e) {
  QLineEdit::focusInEvent(e);
  // force completion when line edit is focued in
  completer()->complete();
}

void Completer_line_edit::slot_text_edited() {
  qDebug() << "text edited";
  // force to show all items when text is empty
  completer()->setCompletionMode(text().isEmpty()? QCompleter::UnfilteredPopupCompletion: QCompleter::PopupCompletion);
  if (text().isEmpty()) {
    // completion list will be hidden now; we will show it again after a delay
    timer.singleShot(100, this, SLOT(slot_call_popup()));
  }
}

void Completer_line_edit::slot_call_popup() {
  // apparently, complete() works only in event handler
  QApplication::postEvent(this, new QEvent(QEvent::User));
}

void Completer_line_edit::customEvent(QEvent *e) {
  QLineEdit::customEvent(e);
  // force completion after text is deleted
  completer()->complete();
}

- Pavel Strakhov