我有一个QTableView，它可以从继承QAbstractItemModel的自定义模型中动态加载数据。该模型同时实现了fetchMore和canFetchMore。
问题是，我希望能够为小型数据集选择所有行，但如果我在视图中点击ctrl-a，它只会选择当前加载的行。
是否有某种机制可以强制QTableView获取更多行？理想情况下，我想显示一个进度条，指示已从模型加载的数据部分。每隔几秒钟，我想强制模型加载更多的数据，但我仍然想让用户与迄今为止加载的数据进行交互。这样，当进度条完成时，用户可以按下ctrl-a并确信所有数据都已选择。
编辑：我有另一个激励性的用例。我想跳到一个特定的行，但如果该行没有加载，我的接口将不起任何作用。
如何强制QAbstractItemModel获取更多（或最多获取一行），然后强制QTableView显示它？
如果我不实现fetchMore和canFetchMore，前面的功能可以工作，但加载表非常慢。当我实现这些方法时，情况正好相反。没有这个问题的答案会导致我的qt接口的可用性出现问题，所以我愿意回答这个问题。
下面是我用来选择一个特定行的方法。
def select_row_from_id(view, _id, scroll=False, collapse=True):
"""
_id is from the iders function (i.e. an ibeis rowid)
selects the row in that view if it exists
"""
with ut.Timer('[api_item_view] select_row_from_id(id=%r, scroll=%r, collapse=%r)' %
(_id, scroll, collapse)):
qtindex, row = view.get_row_and_qtindex_from_id(_id)
if row is not None:
if isinstance(view, QtWidgets.QTreeView):
if collapse:
view.collapseAll()
select_model = view.selectionModel()
select_flag = QtCore.QItemSelectionModel.ClearAndSelect
#select_flag = QtCore.QItemSelectionModel.Select
#select_flag = QtCore.QItemSelectionModel.NoUpdate
with ut.Timer('[api_item_view] selecting name. qtindex=%r' % (qtindex,)):
select_model.select(qtindex, select_flag)
with ut.Timer('[api_item_view] expanding'):
view.setExpanded(qtindex, True)
else:
# For Table Views
view.selectRow(row)
# Scroll to selection
if scroll:
with ut.Timer('scrolling'):
view.scrollTo(qtindex)
return row
return None
如果用户手动滚动过有问题的行，则此功能有效。但是，如果用户没有看到特定的行，则此功能将滚动回视图的顶部。
现在给出答案可能已经太晚了，但也许这对未来的某个人仍然有益。
下面可以找到一个具有canFetchMore和fetchMore方法的列表模型的工作示例+一个具有两个自定义方法的视图：
- 方法，尝试从模型加载更多项（如果模型尚未加载某些项）
- 方法，该方法能够在尚未加载特定行的情况下从模型中获取这些行
示例中的QMainWindow子类有一个计时器，用于重复调用上述第一个方法，每次都强制将另一批项目从模型加载到视图中。在小的时间间隔内批量加载项目可以避免完全阻塞UI线程，并且能够在几乎没有延迟的情况下编辑到目前为止加载的项目。该示例包含一个进度条，显示到目前为止已加载的部分项目。
QMainWindow子类还有一个旋转框，可以选择要在视图中显示的特定行。如果已经从模型中提取了相应的项，则视图只需滚动到它。否则，它将首先从模型中获取此行的项，以同步的方式，即UI阻塞方式。
以下是用python 3.5.2和PyQt5:测试的解决方案的完整代码
import sys
from PyQt5 import QtWidgets, QtCore
class DelayedFetchingListModel(QtCore.QAbstractListModel):
def __init__(self, batch_size=100, max_num_nodes=1000):
QtCore.QAbstractListModel.__init__(self)
self.batch_size = batch_size
self.nodes = []
for i in range(0, self.batch_size):
self.nodes.append('node ' + str(i))
self.max_num_nodes = max(self.batch_size, max_num_nodes)
def flags(self, index):
if not index.isValid():
return QtCore.Qt.ItemIsEnabled
return QtCore.Qt.ItemIsEnabled | QtCore.Qt.ItemIsSelectable | QtCore.Qt.ItemIsEditable;
def rowCount(self, index):
if index.isValid():
return 0
return len(self.nodes)
def data(self, index, role):
if not index.isValid():
return None
if role != QtCore.Qt.DisplayRole:
return None
row = index.row()
if row < 0 or row >= len(self.nodes):
return None
else:
return self.nodes[row]
def setData(self, index, value, role):
if not index.isValid():
return False
if role != QtCore.Qt.EditRole:
return False
row = index.row()
if row < 0 or row >= len(self.nodes):
return False
self.nodes[row] = value
self.dataChanged.emit(index, index)
return True
def headerData(self, section, orientation, role):
if section != QtCore.Qt.Horizontal:
return None
if section != 0:
return None
if role != QtCore.Qt.DisplayRole:
return None
return 'node'
def canFetchMore(self, index):
if index.isValid():
return False
return (len(self.nodes) < self.max_num_nodes)
def fetchMore(self, index):
if index.isValid():
return
current_len = len(self.nodes)
target_len = min(current_len + self.batch_size, self.max_num_nodes)
self.beginInsertRows(index, current_len, target_len - 1)
for i in range(current_len, target_len):
self.nodes.append('node ' + str(i))
self.endInsertRows()
class ListView(QtWidgets.QListView):
def __init__(self, parent=None):
QtWidgets.QListView.__init__(self, parent)
def jumpToRow(self, row):
model = self.model()
if model == None:
return False
num_rows = model.rowCount()
while(row >= num_rows):
res = fetchMoreRows(QtCore.QModelIndex())
if res == False:
return False
num_rows = model.rowCount()
index = model.index(row, 0, QtCore.QModelIndex())
self.scrollTo(index, QtCore.QAbstractItemView.PositionAtCenter)
return True
def fetchMoreRows(self, index):
model = self.model()
if model == None:
return False
if not model.canFetchMore(index):
return False
model.fetchMore(index)
return True
class MainForm(QtWidgets.QMainWindow):
def __init__(self, parent=None):
QtWidgets.QMainWindow.__init__(self, parent)
# Setup the model
self.max_num_nodes = 10000
self.batch_size = 100
self.model = DelayedFetchingListModel(batch_size=self.batch_size, max_num_nodes=self.max_num_nodes)
# Setup the view
self.view = ListView()
self.view.setModel(self.model)
# Update the currently selected row in the spinbox
self.view.selectionModel().currentChanged.connect(self.onCurrentItemChanged)
# Select the first row in the model
index = self.model.index(0, 0, QtCore.QModelIndex())
self.view.selectionModel().clearSelection()
self.view.selectionModel().select(index, QtCore.QItemSelectionModel.Select)
# Setup the spinbox
self.spinBox = QtWidgets.QSpinBox()
self.spinBox.setMinimum(0)
self.spinBox.setMaximum(self.max_num_nodes-1)
self.spinBox.setSingleStep(1)
self.spinBox.valueChanged.connect(self.onSpinBoxNewValue)
# Setup the progress bar showing the status of model data loading
self.progressBar = QtWidgets.QProgressBar()
self.progressBar.setRange(0, self.max_num_nodes)
self.progressBar.setValue(0)
self.progressBar.valueChanged.connect(self.onProgressBarValueChanged)
# Add status bar but initially hidden, will only show it if there's something to say
self.statusBar = QtWidgets.QStatusBar()
self.statusBar.hide()
# Collect all this stuff into a vertical layout
self.layout = QtWidgets.QVBoxLayout()
self.layout.addWidget(self.view)
self.layout.addWidget(self.spinBox)
self.layout.addWidget(self.progressBar)
self.layout.addWidget(self.statusBar)
self.window = QtWidgets.QWidget()
self.window.setLayout(self.layout)
self.setCentralWidget(self.window)
# Setup timer to fetch more data from the model over small time intervals
self.timer = QtCore.QBasicTimer()
self.timerPeriod = 1000
self.timer.start(self.timerPeriod, self)
def onCurrentItemChanged(self, current, previous):
if not current.isValid():
return
row = current.row()
self.spinBox.setValue(row)
def onSpinBoxNewValue(self, value):
try:
value_int = int(value)
except ValueError:
return
num_rows = self.model.rowCount(QtCore.QModelIndex())
if value_int >= num_rows:
# There is no such row within the model yet, trying to fetch more
while(True):
res = self.view.fetchMoreRows(QtCore.QModelIndex())
if res == False:
# We shouldn't really get here in this example since out
# spinbox's range is limited by exactly the number of items
# possible to fetch but generally it's a good idea to handle
# cases like this, when someone requests more rows than
# the model has
self.statusBar.show()
self.statusBar.showMessage("Can't jump to row %d, the model has only %d rows" % (value_int, self.model.rowCount(QtCore.QModelIndex())))
return
num_rows = self.model.rowCount(QtCore.QModelIndex())
if value_int < num_rows:
break;
if num_rows < self.max_num_nodes:
# If there are still items to fetch more, check if we need to update the progress bar
if self.progressBar.value() < value_int:
self.progressBar.setValue(value_int)
elif num_rows == self.max_num_nodes:
# All items are loaded, nothing to fetch more -> no need for the progress bar
self.progressBar.hide()
# Update the selection accordingly with the new row and scroll to it
index = self.model.index(value_int, 0, QtCore.QModelIndex())
selectionModel = self.view.selectionModel()
selectionModel.clearSelection()
selectionModel.select(index, QtCore.QItemSelectionModel.Select)
self.view.scrollTo(index, QtWidgets.QAbstractItemView.PositionAtCenter)
# Ensure the status bar is hidden now
self.statusBar.hide()
def timerEvent(self, event):
res = self.view.fetchMoreRows(QtCore.QModelIndex())
if res == False:
self.timer.stop()
else:
self.progressBar.setValue(self.model.rowCount(QtCore.QModelIndex()))
if not self.timer.isActive():
self.timer.start(self.timerPeriod, self)
def onProgressBarValueChanged(self, value):
if value >= self.max_num_nodes:
self.progressBar.hide()
def main():
app = QtWidgets.QApplication(sys.argv)
form = MainForm()
form.show()
app.exec_()
if __name__ == '__main__':
main()
我还想注意的一件事是，这个例子期望fetchMore方法同步完成它的工作。但在更复杂的方法中，fetchMore实际上不必这么做。如果你的模型从数据库加载项目，那么在UI线程中与数据库同步对话将是个坏主意。相反，fetchMore实现可以启动信号/时隙通信的异步序列，其中某个对象处理在某个后台线程中发生的与数据库的通信。
一个基于Dmitry答案的自用模型类。
class EzQListModel(QAbstractListModel):
items_changed = Signal()
an_item_changed = Signal(int)
def __init__(self, batch_size=100, items_header='Items', parent=None):
super().__init__(parent)
self._batch_size = batch_size
self._current_size = 0
self._items = []
self.items_header = items_header
self.data_getter_mapping = {Qt.DisplayRole: self.get_display_data, Qt.BackgroundRole: self.get_background_data}
@property
def items_size(self):
return len(self._items)
def update_fetch_more(self):
if self.canFetchMore():
self.fetchMore()
return self
@contextlib.contextmanager
def ctx_change_items(self):
yield
self.items_changed.emit()
@contextlib.contextmanager
def ctx_change_an_item(self, index):
yield
self.an_item_changed.emit(index)
def clear_items(self):
with self.ctx_change_items():
self._items.clear()
self._current_size = 0
return self
def append_item(self, x):
with self.ctx_change_items():
self._items.append(x)
return self
def insert_item(self, index, x):
with self.ctx_change_items():
self._items.insert(index, x)
return self
def extend_items(self, items):
with self.ctx_change_items():
self._items.extend(items)
return self
def get_item(self, index):
return self._items[index]
def set_item(self, index, value):
with self.ctx_change_items():
with self.ctx_change_an_item(index):
self._items[index] = value
return self
def flags(self, index):
if not index.isValid():
return Qt.ItemIsEnabled
return Qt.ItemIsEnabled | Qt.ItemIsSelectable | Qt.ItemIsEditable
def rowCount(self, parent=QModelIndex()):
if parent.isValid():
return 0
n = self._current_size
if n <= self.items_size:
return n
else:
self._current_size = self.items_size
return self.items_size
@staticmethod
def get_none_data(index):
return None
def get_display_data(self, index: QModelIndex):
return self._items[index.row()]
@staticmethod
def get_background_data(index: QModelIndex):
palette = QApplication.palette()
return palette.alternateBase() if index.row() % 2 else palette.base()
def data(self, index, role=Qt.DisplayRole):
if not index.isValid():
return None
if self.items_size <= index.row() < 0:
return None
return self.data_getter_mapping.get(role, self.get_none_data)(index)
def setData(self, index, value, role=Qt.EditRole):
if not index.isValid():
return False
if role != Qt.EditRole:
return False
row = index.row()
if self.items_size <= row < 0:
return False
self._items[row] = value
self.dataChanged.emit(index, index)
# print(self.setData.__name__, row, self._items[row], self.data(index))
return True
def headerData(self, section, orientation, role=None):
if orientation != Qt.Horizontal:
return None
if section != 0:
return None
if role != Qt.DisplayRole:
return None
return self.items_header
def canFetchMore(self, parent: QModelIndex = QModelIndex()):
if parent.isValid():
return False
return self._current_size < self.items_size
def fetchMore(self, parent: QModelIndex = QModelIndex()):
if parent.isValid():
return
fcls = FirstCountLastStop().set_first_and_total(self._current_size,
min(self.items_size - self._current_size, self._batch_size))
self.beginInsertRows(parent, fcls.first, fcls.last)
self.endInsertRows()
self._current_size += fcls.total
class FirstCountLastStop:
def __init__(self):
self.first = 0
self.total = 0
self.last = 0
self.stop = 1
def set_first_and_total(self, first, count):
self.first = first
self.total = count
self.stop = first + count
self.last = self.stop - 1
return self