无法从我的测试器类访问画布类中的 paint(图形 g) 方法。

Question

这是待办事项列表，当用户选择5时，图像应在画布上显示，但是我无法从画布上访问油漆（Graphics g）方法上课，在我的测试人员中。

我在测试仪中遇到了一个错误，该错误说无法从静态上下文中引用非静态方法。在情况5中，可变g也无法解决。

这是画布类

import java.awt.*;
import javax.swing.*;
import java.awt.Canvas;

class Motivation extends JFrame {

{
    Motivation a = new Motivation();
    a.setVisible(true);
}

Image img = Toolkit.getDefaultToolkit().getImage("motivation.jpg");

public Motivation() {
    super("motivation");
    getContentPane().add(new Canvas(), BorderLayout.CENTER);
    setSize(500, 500);
    setLocationRelativeTo(null);
    setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
}

class MyCanvas extends Canvas  {
        public void paint(Graphics g) {
            g.drawImage(img, 5, 5, this);
            paint(g);
        }
    }
}

这是测试仪

import java.awt.*;
import java.io.*;
import java.util.Scanner;
import java.util.concurrent.atomic.AtomicReference;
public class ToDoListTester {

public static void main(String[] args) throws IOException {
    AtomicReference<String> userName = new AtomicReference<String>();
    Scanner name = new Scanner(System.in);
    System.out.println("n FINALS TO-DO LIST n");
    System.out.println("Please Enter Your name");
    userName.set(name.nextLine());
    System.out.println("Hello " + userName + "!");
    int select = -1;
    while (select != 0) {
        select = ToDoList.menu();
        switch (select) {
            case 1:                             // case: different form of for/while loop. If the user selects 1, show the To Do list
                ToDoList.showList();
                break;
            case 2:                             //if the user selects 2, show the To Do list
                ToDoList.addTask();
                break;
            case 3:                             //if the user selects 3, show the To Do list
                ToDoList.removeTask();
                break;
            case 4:
                ToDoList.setTimer();                     //if the user selects 4, the countdown timer is started.
                break;
            case 5:
                Motivation motivateMe = new Motivation();
                motivateMe.MyCanvas.paint(Graphics g);
            case 0:                             //if the user selects 0, the program is stopped, takes us out of the loop.
                break;
            default:                            // different form of else. If the user does something we don't recognize/
                System.out.println("Well you're just a little rebel aren't you?");
                System.out.println("Try again.");
                System.out.println("Select 1 to display your To Do List.");
                System.out.println("Select 2 to add a task to your To Do list.");
                System.out.println("Select 3 to remove a task from your To Do list.");
                System.out.println("Select 4 to set a countdown timer for your task.");
                System.out.println("Select 5 for some motivation. ");
                System.out.println("Select 0 to exit the program.");
        }
    }
}

}

Answer 1

永远不要直接调用油漆（...）方法，秋千将确定何时需要重新粉刷组件。然后，秋千将创建用于绘画方法使用的图形对象。

如果要手动重新粉刷组件，则使用：

someComponent.repaint();

尽管在您的情况下，这是无需这样做的。创建组件后，您实际上必须将画布添加到框架上才能涂漆。

另外，为什么要使用帆布？那是一个AWT组件。使用秋千时，您应该使用jpanel。

实际上，如果您只是想显示图像，则使用jlabel。阅读有关如何使用图标以获取更多信息和工作示例的Swing教程中的部分。