【问题标题】：Clean Canvas in kivy language from other class使用其他班级的 kivy 语言清洁 Canvas
【发布时间】：2017-09-28 00:36:23
【问题描述】：

我刚开始在我的应用程序中使用 Kivy，但遇到了问题。我尝试清理我的画布，但我无法将按钮与画布相关联

class DrawInput(Widget):
def on_touch_down(self, touch):
    print(touch)
    with self.canvas:
        touch.ud["line"] = Line(points=(touch.x, touch.y), width=100)

def on_touch_move(self, touch):
    #print(touch)
    touch.ud["line"].points += (touch.x, touch.y)

def on_touch_up(self, touch):
    self.export_to_png("roy.png")
    print("RELEASED!", touch)

def cleaner(self):
    self.canvas.clear()


class AnotherScreen(Screen):
pass

presentation = Builder.load_file("main2.kv")

class MainApp(App):

def build(self):
    return presentation

def clear_canvas(self, obj):

MainApp().run()

这里是main2.kv

GridLayout:
    cols: 2
    Button:
        on_release: root.change_text()
        color: 0,1,0,1
        font_size: 25
        size_hint: 0.3,0.2
        text: root.random_number
        pos_hint: {"right":1, "top":1}
    DrawInput
    Button:
        on_release: root.clean()
        color: 0,1,0,1
        font_size: 25
        size_hint: 0.3,0.2
        text: "Clear"

我的问题是我需要从其他类调用 Clean Method，但是当我尝试它时它说我需要发送“Self”，有人可以帮助我吗？只是试图清理与 DrawInput 相关的画布

【问题讨论】：

你实现了两种方法，即cleaner和clear_canvas。您要调用哪种方法？您的 clear_canvas 为空（缺少代码）。

标签： python kivy

【解决方案1】：

您必须使用 ObjectProperty 连接到 DrawInput 子小部件以引用更清洁的方法。详情请参考以下示例。

示例

main.py

from kivy.app import App
from kivy.uix.widget import Widget
from kivy.graphics import Line
from kivy.uix.screenmanager import ScreenManager, Screen
from kivy.properties import ObjectProperty


class DrawInput(Widget):
    def on_touch_down(self, touch):
        print(touch)
        with self.canvas:
            touch.ud["line"] = Line(points=(touch.x, touch.y), width=100)

    def on_touch_move(self, touch):
        #print(touch)
        touch.ud["line"].points += (touch.x, touch.y)

    def on_touch_up(self, touch):
        # self.export_to_png("roy.png")
        self.export_to_png("kivy-logo-black-64.png")
        print("RELEASED!", touch)

    def cleaner(self):
        print("cleaner: ", self)
        self.canvas.clear()


class FirstScreen(Screen):
    draw = ObjectProperty()


class AnotherScreen(Screen):
    pass


class Manager(ScreenManager):
    mgr = ObjectProperty()

    def change_text(self):
        pass

    def random_number(self):
        pass

    def clean(self):
        print("clean: ", self)
        self.mgr.draw.cleaner()


class TestApp(App):

    def build(self):
        return Manager()


if __name__ == "__main__":
    TestApp().run()

test.kv

#:kivy 1.10.0

<DrawInput>:

<Manager>:
    mgr: first_screen
    FirstScreen:
        id: first_screen
    AnotherScreen:

<FirstScreen>:
    draw: draw_input
    GridLayout:
        cols: 2
        Button:
            on_release: app.root.change_text()
            color: 0,1,0,1
            font_size: 25
            size_hint: 0.3, 0.2
            # text: app.root.random_number()
            text: "123"
            pos_hint: {"right":1, "top":1}

        DrawInput:
            id: draw_input

        Button:
            on_release: app.root.clean()
            color: 0,1,0,1
            font_size: 25
            size_hint: 0.3, 0.2
            text: "Clear"

<AnotherScreen>:

输出

【讨论】：