Question

这是一个待办事项列表，当用户选择5时，图像应显示在画布上，但我无法在我的测试程序中从Canvas类访问paint（Graphics g）方法。

我在测试程序中收到错误，指出无法从静态上下文引用非静态方法。在案例5中，变量g也无法解析。

这是Canvas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);
        }
    }
}

这是测试人员

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

不要直接调用paint（...）方法，Swing将确定何时需要重新绘制组件。然后，Swing将创建要由绘制方法使用的Graphics对象。

如果要手动重新绘制组件，请使用：

someComponent.repaint();

虽然在你的情况下，然后没有必要这样做。在创建组件之后，您实际上必须将Canvas添加到框架中以便绘制它。

另外，你为什么要使用Canvas？这是一个AWT组件。使用Swing时应该使用JPanel。

实际上，如果您只是想显示图像，那么请使用JLabel。阅读How to Use Icons上Swing教程中的部分，了解更多信息和工作示例。

无法从我的Tester类

1 个答案: