为什么我的 QFileSystemModel QModelIndex 无法获取子节

问题描述

我正在学习 pyqt 中的模型/视图架构，但是当我遵循 ，2) 指出:

缓存和性能

与 QDirModel 不同，QFileSystemModel 使用单独的线程来填充本身所以它不会导致主线程作为文件系统挂起正在被查询.调用 rowCount() 将返回 0，直到模型填充目录.

QFileSystemModel 保存一个包含文件信息的缓存.缓存是使用 QFileSystemWatcher 自动保持最新.

<小时><块引用>

QModelIndex QFileSystemModel::setRootPath(const QString &newPath)

如果路径改变，将发出 rootPathChanged() 信号.

注意:此功能不会改变模型的结构或修改视图可用的数据.换言之，根"模型未更改为仅包含文件和目录文件系统中newPath指定的目录.

^强调我的

加载过程在不同的线程中执行，并且加载是异步完成的，因此在您发出请求时，模型尚未加载.

解决方案:

解决方案是在加载后请求信息，该信息将通过 的 noreferrer">directoryLoaded 信号QFileSystemModel:

from PyQt5.QtCore import pyqtSlot, QDir从 PyQt5.QtWidgets 导入 QApplication、QFileSystemModel、QPushButton类 DemoB(QPushButton):def __init__(self, parent=None):super().__init__(父)self.clicked.connect(self.on_clicked)self.model = QFileSystemModel(self)self.model.directoryLoaded.connect(self.on_directoryLoaded)@pyqtSlot()def on_clicked(self):self.model.setRootPath(QDir.homePath())@pyqtSlot(str)def on_directoryLoaded(自我，目录):parentIndex = self.model.index(目录)对于范围内的行(self.model.rowCount(parentIndex)):index = self.model.index(row, 0, parentIndex)打印(索引，index.data())如果 __name__ == "__main__":导入系统应用程序 = QApplication(sys.argv)w = DemoB()w.show()sys.exit(app.exec_())

I am learn about Model/View architecture in pyqt, but when i follow the Using model indexes instruction and try to write a demo in pyqt5 style.The QModelIndex couldn't get child node information?

The code:

class DemoB(QPushButton):
    def __init__(self):
        super().__init__()

        self.clicked.connect(self.on_clicked)

    def on_clicked(self, checked):
        model = QFileSystemModel()
        model.setRootPath(QDir.homePath())
        parentIndex = model.index(QDir.homePath())
        print(parentIndex.data() )
        print(parentIndex, model.rowCount(parentIndex), QDir.homePath())
        for row in range(model.rowCount(parentIndex)):
            index = model.index(row, 0, parentIndex)
            print(index, index.data())

The result:

My folder:

Explanation:

As the docs(1, 2) points out:

Caching and Performance

QFileSystemModel will not fetch any files or directories until setRootPath() is called. This will prevent any unnecessary querying on the file system until that point such as listing the drives on Windows.

Unlike QDirModel, QFileSystemModel uses a separate thread to populate itself so it will not cause the main thread to hang as the file system is being queried. Calls to rowCount() will return 0 until the model populates a directory.

QFileSystemModel keeps a cache with file information. The cache is automatically kept up to date using the QFileSystemWatcher.

QModelIndex QFileSystemModel::setRootPath(const QString &newPath)

Sets the directory that is being watched by the model to newPath by installing a file system watcher on it. Any changes to files and directories within this directory will be reflected in the model.

If the path is changed, the rootPathChanged() signal will be emitted.

Note: This function does not change the structure of the model or modify the data available to views. In other words, the "root" of the model is not changed to include only files and directories within the directory specified by newPath in the file system.

^{emphasis mine}

The loading process is executed in a different thread and the loading is done asynchronously, so at the time you make the request the model is not yet loaded.

Solution:

The solution is to request the information after it has been loaded that will be notified through the directoryLoaded signal of QFileSystemModel:

from PyQt5.QtCore import pyqtSlot, QDir
from PyQt5.QtWidgets import QApplication, QFileSystemModel, QPushButton


class DemoB(QPushButton):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.clicked.connect(self.on_clicked)
        self.model = QFileSystemModel(self)
        self.model.directoryLoaded.connect(self.on_directoryLoaded)

    @pyqtSlot()
    def on_clicked(self):
        self.model.setRootPath(QDir.homePath())

    @pyqtSlot(str)
    def on_directoryLoaded(self, directory):
        parentIndex = self.model.index(directory)
        for row in range(self.model.rowCount(parentIndex)):
            index = self.model.index(row, 0, parentIndex)
            print(index, index.data())


if __name__ == "__main__":
    import sys

    app = QApplication(sys.argv)
    w = DemoB()
    w.show()
    sys.exit(app.exec_())

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