QLineEdit:将光标位置设置为焦点开始

Question

我有一个QLineEdit输入掩码,因此可以轻松输入(或粘贴)某种代码.因为QLineEdit即使没有文本也可以将光标放在任何位置(因为输入掩码中有一个占位符):

如果人们不小心且不专心,这会导致他们在文本框的中间键入,而他们应该在开头打字.我尝试了通过安装事件过滤器确保光标在焦点开始时的简单方法:

bool MyWindowPrivate::eventFilter(QObject * object, QEvent * event)
{
    if (object == ui.tbFoo && event->type() == QEvent::FocusIn) {
        ui.tbFoo->setCursorPosition(0);
    }
    return false;
}

这与keybaord焦点一起工作正常,即按下⇆或⇧+时⇆,但是当用鼠标点击时,光标总是在我点击的位置结束.我的猜测是,QLineEdit设置在点击自己的光标位置后它得到了关注,从而解开我的位置变化.

深入挖掘,点击¹,从而按以下顺序更改焦点时,会引发以下事件:

1. FocusIn
2. MouseButtonPress
3. MouseButtonRelease

我无法在事件过滤器中完全捕获鼠标点击,因此有一种很好的方法可以将光标位置设置为仅在控件被聚焦时启动(无论是通过鼠标还是键盘)？

---

¹旁注:我讨厌Qt没有关于此类常见场景的信号/事件订单的任何文档.

Answer 1

下面是一个实现,它被分解为一个单独的类.它将光标的设置推迟到为对象发布任何待处理事件之后,从而回避事件顺序的问题.

#include <QApplication>
#include <QLineEdit>
#include <QFormLayout>
#include <QMetaObject>

// Note: A helpful implementation of
// QDebug operator<<(QDebug str, const QEvent * ev)
// is given in http://stackoverflow.com/q/22535469/1329652

/// Returns a cursor to zero position on a QLineEdit on focus-in.
class ReturnOnFocus : public QObject {
   Q_OBJECT
   /// Catches FocusIn events on the target line edit, and appends a call
   /// to resetCursor at the end of the event queue.
   bool eventFilter(QObject * obj, QEvent * ev) {
      QLineEdit * w = qobject_cast<QLineEdit*>(obj);
      // w is nullptr if the object isn't a QLineEdit
      if (w && ev->type() == QEvent::FocusIn) {
         QMetaObject::invokeMethod(this, "resetCursor",
                                   Qt::QueuedConnection, Q_ARG(QWidget*, w));
      }
      // A base QObject is free to be an event filter itself
      return QObject::eventFilter(obj, ev);
   }
   // Q_INVOKABLE is invokable, but is not a slot
   /// Resets the cursor position of a given widget.
   /// The widget must be a line edit.
   Q_INVOKABLE void resetCursor(QWidget * w) {
      static_cast<QLineEdit*>(w)->setCursorPosition(0);
   }
public:
   ReturnOnFocus(QObject * parent = 0) : QObject(parent) {}
   /// Installs the reset functionality on a given line edit
   void installOn(QLineEdit * ed) { ed->installEventFilter(this); }
};

class Ui : public QWidget {
   QFormLayout m_layout;
   QLineEdit m_maskedLine, m_line;
   ReturnOnFocus m_return;
public:
   Ui() : m_layout(this) {
      m_layout.addRow(&m_maskedLine);
      m_layout.addRow(&m_line);
      m_maskedLine.setInputMask("NNNN-NNNN-NNNN-NNNN");
      m_return.installOn(&m_maskedLine);
   }
};

int main(int argc, char *argv[])
{
   QApplication a(argc, argv);
   Ui ui;
   ui.show();
   return a.exec();
}

#include "main.moc"