PyQt5: How to scroll text in QTextEdit automatical

Question

I would like to ask how to make the text in QTextEdit scoll, to achieve an animational effect. The animational effect should be something like what in the video shows: https://www.youtube.com/watch?v=MyeuGdXv4XM

With PyQt I want to get this effect: The text should be scolled automatically at a speed of 2 lines/second downwards, till it reaches the end and stops.

In my code below, when the button is clicked, the text is shown in QTextEdit-Widget. The text is very long, so that the scroll bar is shown.

My Problem: I dont know how to make the animation effect. Thus I would like to ask your help to correct my code.

# -*- coding: utf-8 -*-

from PyQt5.QtWidgets import *
from PyQt5.QtGui import *
from PyQt5.QtCore import *

import sys
import time


list_longText = [" long text 1 - auto scrolling " * 1000, " long text 2 - auto scrolling " * 2000]

class Worker(QObject):
    finished = pyqtSignal()
    strTxt = pyqtSignal(str)

    def __init__(self, parent=None):
        super(Worker, self).__init__(parent)

    @pyqtSlot()
    def onJob(self):
        for i in range(2):
            self.strTxt.emit(list_longText[i])
            time.sleep(2)

class MyApp(QWidget):
    def __init__(self):
        super(MyApp, self).__init__()
        self.setFixedSize(600, 400)
        self.setObjectName("window")

        self.initUI()


    def initUI(self):

        self.txt = QTextEdit("", self)
        self.btn = QPushButton("Button", self)
        self.btn.clicked.connect(self.start)

        self.layout = QHBoxLayout(self)
        self.layout.addWidget(self.txt)
        self.layout.addWidget(self.btn)
        self.setLayout(self.layout)

        self.show()

    def start(self):
        self.thread = QThread()
        self.obj = Worker()

        self.obj.strTxt.connect(self.showText)
        self.obj.moveToThread(self.thread)
        self.obj.finished.connect(self.thread.quit)
        self.thread.started.connect(self.obj.onJob)
        self.thread.start()

    def showText(self, str):
        self.txt.setText("{}".format(str))
        self.autoScroll()

    def autoScroll(self):
        vsb = self.txt.verticalScrollBar()
        if vsb.value() <= vsb.maximum():
            vsb.setValue(vsb.value() + 2)
            time.sleep(1)


if __name__ == "__main__":
    app = QApplication(sys.argv)
    window = MyApp()
    sys.exit(app.exec_())

Thanks very much for the help!

Answer 1

The task you want is not heavy, it is periodic so using a thread is inappropriate, for this task we can use QVariantAnimation.

The other part is to create a method that moves to a certain line of text for it we use QTextCursor next to findBlockByLineNumber() of QTextDocument.

And for the last one we must start moving to the last initial visible for it we use the cursorForPosition() method through the size of the viewport().

longText = "\n".join(["{}: long text - auto scrolling ".format(i) for i in range(100)])

class AnimationTextEdit(QTextEdit):
    def __init__(self, *args, **kwargs):
        QTextEdit.__init__(self, *args, **kwargs)
        self.animation = QVariantAnimation(self)
        self.animation.valueChanged.connect(self.move)

    @pyqtSlot()
    def startAnimation(self):
        self.animation.stop()
        lines_per_second = 2
        self.moveToLine(0)
        p = QPoint(self.viewport().width() - 1, self.viewport().height() - 1)
        cursor = self.cursorForPosition(p)
        self.animation.setStartValue(cursor.blockNumber())
        self.animation.setEndValue(self.document().blockCount()-1)
        self.animation.setDuration(self.animation.endValue()*1000/lines_per_second)
        self.animation.start()

    @pyqtSlot(QVariant)
    def move(self, i):
        cursor = QTextCursor(self.document().findBlockByLineNumber(i))
        self.setTextCursor(cursor)

class MyApp(QWidget):
    def __init__(self):
        super(MyApp, self).__init__()
        self.setFixedSize(600, 400)
        self.txt = AnimationTextEdit(self)
        self.btn = QPushButton("Start", self)
        self.layout = QHBoxLayout(self)
        self.layout.addWidget(self.txt)
        self.layout.addWidget(self.btn)
        self.txt.append(longText)
        self.txt.move(0)
        self.btn.clicked.connect(self.txt.startAnimation)


if __name__ == "__main__":
    app = QApplication(sys.argv)
    window = MyApp()
    window.show()
    sys.exit(app.exec_())

Update:

if you want a continuous movement you must use verticalScrollBar():

longText = "\n".join(["{}: long text - auto scrolling ".format(i) for i in range(100)])

class AnimationTextEdit(QTextEdit):
    def __init__(self, *args, **kwargs):
        QTextEdit.__init__(self, *args, **kwargs)
        self.animation = QVariantAnimation(self)
        self.animation.valueChanged.connect(self.moveToLine)

    @pyqtSlot()
    def startAnimation(self):
        self.animation.stop()
        self.animation.setStartValue(0)
        self.animation.setEndValue(self.verticalScrollBar().maximum())
        self.animation.setDuration(self.animation.endValue()*4)
        self.animation.start()

    @pyqtSlot(QVariant)
    def moveToLine(self, i):
        self.verticalScrollBar().setValue(i)

class MyApp(QWidget):
    def __init__(self):
        super(MyApp, self).__init__()
        self.setFixedSize(600, 400)
        self.txt = AnimationTextEdit(self)
        self.btn = QPushButton("Start", self)
        self.layout = QHBoxLayout(self)
        self.layout.addWidget(self.txt)
        self.layout.addWidget(self.btn)
        self.txt.append(longText)
        self.txt.moveToLine(0)
        self.btn.clicked.connect(self.txt.startAnimation)


if __name__ == "__main__":
    app = QApplication(sys.argv)
    window = MyApp()
    window.show()
    sys.exit(app.exec_())