如何在 Python 的 Tkinter 的类中使用 slider.on_changed()

Posted 2023-04-14

【中文标题】如何在 Python 的 Tkinter 的类中使用 slider.on_changed()

【英文标题】：How to use slider.on_changed() within a class in Tkinter in Python

【发布时间】：2021-03-03 07:13:27

【问题描述】：

我正在尝试使用水平滑块来更改绘图的 xlim。但首先，我不知道如何使用 on_changed() 方法让滑块更新。我对类和对象如何相互交互没有深入的了解。

我使用这个滑块示例作为模板：

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.widgets import Slider, Button, RadioButtons

fig, ax = plt.subplots()
plt.subplots_adjust(left=0.25, bottom=0.25)
t = np.arange(0.0, 1.0, 0.001)
a0 = 5
f0 = 3
delta_f = 5.0
s = a0 * np.sin(2 * np.pi * f0 * t)
l, = plt.plot(t, s, lw=2)
ax.margins(x=0)

axcolor = 'lightgoldenrodyellow'
axfreq = plt.axes([0.25, 0.1, 0.65, 0.03], facecolor=axcolor)
axamp = plt.axes([0.25, 0.15, 0.65, 0.03], facecolor=axcolor)

sfreq = Slider(axfreq, 'Freq', 0.1, 30.0, valinit=f0, valstep=delta_f)
samp = Slider(axamp, 'Amp', 0.1, 10.0, valinit=a0)


def update(val):
    amp = samp.val
    freq = sfreq.val
    l.set_ydata(amp*np.sin(2*np.pi*freq*t))
    fig.canvas.draw_idle()


sfreq.on_changed(update)
samp.on_changed(update)

resetax = plt.axes([0.8, 0.025, 0.1, 0.04])
button = Button(resetax, 'Reset', color=axcolor, hovercolor='0.975')


def reset(event):
    sfreq.reset()
    samp.reset()
button.on_clicked(reset)

rax = plt.axes([0.025, 0.5, 0.15, 0.15], facecolor=axcolor)
radio = RadioButtons(rax, ('red', 'blue', 'green'), active=0)


def colorfunc(label):
    l.set_color(label)
    fig.canvas.draw_idle()
radio.on_clicked(colorfunc)

plt.show()

在我的应用中实现时遇到问题的部分是：

sfreq.on_changed(update)
samp.on_changed(update)

如果您使用 plt.show() 打开绘图，它可以正常工作，但如果您像我在下面所做的那样将它打包到画布中，它就会停止工作。任何想法为什么？

这是我的应用程序的代码： 更新：我简化了代码以专注于问题。

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.widgets import Slider, Button, RadioButtons
from matplotlib.figure import Figure
from matplotlib.backends.backend_tkagg import(FigureCanvasTkAgg, NavigationToolbar2Tk)

from tkinter import *
import tkinter as tk

global running
running = True

global graph_exists
graph_exists = False

class MyApp:
    def __init__(self, parent):
        self.myParent = parent ###remember my parent, the root
        self.sfreq = 0
        self.samp = 0

        
        
    def run(self):
        self.fig, self.ax = plt.subplots()
        plt.subplots_adjust(left=0.25, bottom=0.25)
        self.t = np.arange(0.0, 1.0, 0.001)
        a0 = 5
        f0 = 3
        delta_f = 5.0
        s = a0 * np.sin(2 * np.pi * f0 * self.t)
        self.l, = plt.plot(self.t, s, lw=2)
        self.ax.margins(x=0)

        axcolor = 'lightgoldenrodyellow'
        axfreq = plt.axes([0.25, 0.1, 0.65, 0.03], facecolor=axcolor)
        axamp = plt.axes([0.25, 0.15, 0.65, 0.03], facecolor=axcolor)

        self.sfreq = Slider(axfreq, 'Freq', 0.1, 30.0, valinit=f0, valstep=delta_f)
        self.samp = Slider(axamp, 'Amp', 0.1, 10.0, valinit=a0)

        canvas = FigureCanvasTkAgg(self.fig, root)
        canvas.draw()
        canvas.get_tk_widget().pack(side=tk.TOP, fill=tk.BOTH, expand=1)
        graph_exists = True

        

    def update(self, val):
        amp = self.samp.val
        freq = self.sfreq.val
        self.l.set_ydata(amp*np.sin(2*np.pi*freq*self.t))
        self.fig.canvas.draw_idle()

    if graph_exists:
        self.sfreq.on_changed(update)
        self.samp.on_changed(update)
        

#Run the event loop
root = tk.Tk()
myapp = MyApp(root)
myapp.run()
root.mainloop()

【问题讨论】：

sfreq 和 samp 上缺少前缀 self.。

谢谢。没有解决问题，但更近了一步。我更新了问题以反映这一点。

你在MyApp.__init__()里面调用了self.main_graph.update_on_change()，但是那个时候self.sfreq和self.samp还没有创建。尝试删除该行。

啊。我明白你的意思了。这样就消除了错误，但那是因为滑块现在不做任何事情。如何告诉它检查 graph_exists 是否存在，然后列出 on_changed()？

创建两个Slider后可以调用这两个.on_changed(self.update)。您还需要像 def update(self, val) 一样定义 update()。但是，根据answer的其他问题，您需要在绘图之前将图形添加到画布中。

【参考方案1】：

正如我评论中的链接中所说，您需要在绘图之前将图形添加到画布，否则滑块不起作用。您还应该在创建滑块后调用on_changed(...)。

    def run(self):
        self.fig, self.ax = plt.subplots()
        canvas = FigureCanvasTkAgg(self.fig, root)  # add the figure to canvas before plotting
        plt.subplots_adjust(left=0.25, bottom=0.25)
        self.t = np.arange(0.0, 1.0, 0.001)
        a0 = 5
        f0 = 3
        delta_f = 5.0
        s = a0 * np.sin(2 * np.pi * f0 * self.t)
        self.l, = plt.plot(self.t, s, lw=2)
        self.ax.margins(x=0)

        axcolor = 'lightgoldenrodyellow'
        axfreq = plt.axes([0.25, 0.1, 0.65, 0.03], facecolor=axcolor)
        axamp = plt.axes([0.25, 0.15, 0.65, 0.03], facecolor=axcolor)

        self.sfreq = Slider(axfreq, 'Freq', 0.1, 30.0, valinit=f0, valstep=delta_f)
        self.samp = Slider(axamp, 'Amp', 0.1, 10.0, valinit=a0)
        ### setup on_changed callbacks
        self.sfreq.on_changed(self.update) # use 'self.update' instead of 'update'
        self.samp.on_changed(self.update)
        ###
        #canvas = FigureCanvasTkAgg(self.fig, root)
        canvas.draw()
        canvas.get_tk_widget().pack(side=tk.TOP, fill=tk.BOTH, expand=1)
        graph_exists = True

【参考方案2】：

您的代码的问题是永远不会调用方法update...您需要将部分if graph_exists 放入run 方法中。此外，正如@acw1668 分享的帖子中所建议的，您还需要在绘图之前将图形添加到画布中。

试试下面的代码

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.widgets import Slider, Button, RadioButtons
from matplotlib.figure import Figure
from matplotlib.backends.backend_tkagg import(FigureCanvasTkAgg, NavigationToolbar2Tk)

from tkinter import *
import tkinter as tk

global running
running = True

global graph_exists
graph_exists = False

class MyApp:

    def __init__(self, parent):
        self.myParent = parent ###remember my parent, the root
        self.sfreq = 0
        self.samp = 0

    def run(self):
        self.fig, self.ax = plt.subplots()
        canvas = FigureCanvasTkAgg(self.fig, root)
        canvas.get_tk_widget().pack(side=tk.TOP, fill=tk.BOTH, expand=1)
        
        plt.subplots_adjust(left=0.25, bottom=0.25)
        self.t = np.arange(0.0, 1.0, 0.001)
        a0 = 5
        f0 = 3
        delta_f = 5.0
        s = a0 * np.sin(2 * np.pi * f0 * self.t)
        self.l, = plt.plot(self.t, s, lw=2)
        self.ax.margins(x=0)

        axcolor = 'lightgoldenrodyellow'
        axfreq = plt.axes([0.25, 0.1, 0.65, 0.03], facecolor=axcolor)
        axamp = plt.axes([0.25, 0.15, 0.65, 0.03], facecolor=axcolor)

        self.sfreq = Slider(axfreq, 'Freq', 0.1, 30.0, valinit=f0, valstep=delta_f)
        self.samp = Slider(axamp, 'Amp', 0.1, 10.0, valinit=a0)
        graph_exists = True
        
        if graph_exists:
            self.sfreq.on_changed(self.update)
            self.samp.on_changed(self.update)

    def update(self, val):
        print('inside update')
        amp = self.samp.val
        freq = self.sfreq.val
        self.l.set_ydata(amp*np.sin(2*np.pi*freq*self.t))
        
        self.fig.canvas.draw_idle()
        

#Run the event loop
root = tk.Tk()
myapp = MyApp(root)
myapp.run()
root.mainloop()