java - Swing Java 重绘无法使用 2 个 jpanels 工作

Question

正如您从代码中看到的，我希望在 DrawingPanel 上看到一个矩形，但我不确定为什么 repaint() 方法不起作用。任何帮助都感激不尽。我也尝试过重新验证方法，但这也不起作用。

这是我的类(class):

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

public class Designer extends JFrame {

static JFrame f = new Designer();

JSplitPane splitPane = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT);
DrawingPanel drawingPanel = new DrawingPanel();
PropertyPanel propertyPanel = new PropertyPanel();

 public Designer(){

    Rectangle bounds = GraphicsEnvironment
            .getLocalGraphicsEnvironment()
            .getMaximumWindowBounds();

    splitPane.setTopComponent(propertyPanel);
    splitPane.setBottomComponent(drawingPanel);

    add(splitPane, BorderLayout.CENTER);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(bounds);
    setVisible(true);

 }

 public static void main(String[] args) {
    System.out.println("App started...");
 }
}

第一个 Jpanel 的类:PropertyPanel.Java

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

public class PropertyPanel extends JPanel {

  private DrawingPanel drawingPanel = new DrawingPanel();

  public PropertyPanel(){

    JButton addShapesBtn = new JButton("Add");

    addShapesBtn.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            drawingPanel.addRectangle();
        }
    });
    add(addShapesBtn);
  }

}

第二个 Jpanel 的类:DrawingPanel.Java

import javax.swing.*;
import java.awt.*;
import java.util.ArrayList;
import java.util.List;

public class DrawingPanel extends JPanel{

  private List<Rectangle> squares = new ArrayList<Rectangle>();


 @Override
 protected void paintComponent(Graphics g) {
    super.paintComponent(g);

    Graphics2D g2 = (Graphics2D) g;

    System.out.println("painting");

    for (Rectangle rect : squares) {
        g2.draw(rect);
    }

}


  public void addRectangle() {

    Rectangle rectx = new Rectangle(10, 10, 100, 100);
    squares.add(rectx);
    repaint(); <-- this is not working
  }
}

Answer 1

你的重画效果很好。您的问题是您正在对错误 DrawingPanel 实例调用 addRectangle() ，而不是当前在 GUI 中显示的实例。要解决此问题，请将显示的引用传递给需要调用该方法的代码。

要查看这是否正确，只需在此页面中搜索 new DrawingPanel() 即可。您应该在您自己的代码(以及您发布的代码)中仅看到此内容一次。您会看到它两次，这意味着您已经创建了该实例的两个实例。

例如，更改此:

public class PropertyPanel extends JPanel {   
    private DrawingPanel drawingPanel = new DrawingPanel();

    public PropertyPanel(){

对此:

public class PropertyPanel extends JPanel {    
    private DrawingPanel drawingPanel;  // don't create new

    public PropertyPanel(DrawingPanel drawingPanel){
        this.drawingPanel = drawingPanel;

然后在创建时将真正的 DrawingPanel 传递到此对象中:

DrawingPanel drawingPanel = new DrawingPanel();
PropertyPanel propertyPanel = new PropertyPanel(drawingPanel);

<小时/>

更好的是:以 M-V-C 方式构建代码，并使用依赖注入(inject)来建立连接——但这对于简单的 GUI 来说可能有点过分了。