無法將項目添加到自定義JPanel

Question

我的問題是我創建了一個繪製漸變作爲背景的JPanel。但是當我去添加組件（如JButton）時，它什麼都不做......

請幫忙！

import java.awt.Color; 
import java.awt.Dimension; 
import java.awt.Font; 
import java.awt.GradientPaint; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.Window; 
import java.awt.event.WindowEvent; 
import java.awt.event.WindowFocusListener; 
import java.beans.PropertyChangeEvent; 
import java.beans.PropertyChangeListener; 
import javax.swing.JComponent; 
import javax.swing.JPanel; 
import javax.swing.SwingUtilities; 


public class CocoaTrashBar extends JPanel { 
    String titleText = ""; 
    Color topLineColor = new Color(128, 128, 128); 
    Color bottomLineColor = new Color(69, 69, 69); 
    Color gradientTop = new Color(116, 116, 116); 
    Color gradientBottom = new Color(81, 81, 81); 


    public CocoaTrashBar() { 
     setDefaults(); 
    } 


    public CocoaTrashBar(String title) { 
     setDefaults(); 
     this.titleText = title; 
    } 


    public void setTitle(String title) { 
     this.titleText = title; 
     this.repaint(); 
    } 


    private void setDefaults() { 
     super.setOpaque(true); 
     this.setPreferredSize(new Dimension(0, 24)); 
     installWindowFocusListener(new WindowFocusListener() { 
      public void windowGainedFocus(WindowEvent e) { 
       topLineColor = new Color(128, 128, 128); 
       bottomLineColor = new Color(69, 69, 69); 
       gradientTop = new Color(116, 116, 116); 
       gradientBottom = new Color(81, 81, 81); 
       repaintComponent(); 
      } 
      public void windowLostFocus(WindowEvent e) { 
       topLineColor = new Color(171, 171, 171); 
       bottomLineColor = new Color(103, 103, 103); 
       gradientTop = new Color(156, 156, 156); 
       gradientBottom = new Color(121, 121, 121); 
       repaintComponent(); 
      } 
     }, this); 
    } 


    private static void installWindowFocusListener(
      WindowFocusListener focusListener, JComponent component) { 
     component.addPropertyChangeListener("Frame.active", 
       createFrameFocusPropertyChangeListener(focusListener, component)); 
    } 


    private static PropertyChangeListener createFrameFocusPropertyChangeListener(
      final WindowFocusListener focusListener, final JComponent component) { 
     return new PropertyChangeListener() { 
      public void propertyChange(PropertyChangeEvent evt) { 
       Window window = SwingUtilities.getWindowAncestor(component); 
       boolean hasFocus = (Boolean) component.getClientProperty("Frame.active"); 
       if (hasFocus) { 
        focusListener.windowGainedFocus(
          new WindowEvent(window, WindowEvent.WINDOW_GAINED_FOCUS)); 
       } else { 
        focusListener.windowLostFocus(
          new WindowEvent(window, WindowEvent.WINDOW_LOST_FOCUS)); 
       } 
      } 
     }; 
    } 


    private void repaintComponent() { 
     this.repaint(); 
    } 


    @Override 
    public void paint(Graphics g) { 
     super.paintComponent(g); 
     Graphics2D g2d =(Graphics2D)g; 
     // Draw first line 
     g2d.setPaint(topLineColor); 
     g2d.drawLine(0, 0, this.getWidth(), 0); 
     // Draw last line 
     g2d.setPaint(bottomLineColor); 
     g2d.drawLine(0, 23, this.getWidth(), 23); 
     // Draw gradient 
     GradientPaint gradient = new GradientPaint(
       this.getX(), 
       this.getY()+1, 
       gradientTop, 
       this.getX(), 
       this.getHeight()-1, 
       gradientBottom); 
     g2d.setPaint(gradient); 
     g2d.fillRect(this.getX(), this.getY()+1, this.getWidth(), this.getHeight()-2); 
     if(titleText != null) { 
      g2d.setFont(new Font("", Font.BOLD, 13)); 
      g2d.setColor(Color.WHITE); 
      g2d.drawString(titleText, 10, 16); 
     } 
     g.dispose(); 
    } 

} 

Answer 1

的問題是在你paint方法覆蓋調用paintComponent

與此更換你的paint方法：

protected void paintComponent(Graphics g) 
{ 
    if (isOpaque()) 
    { 
     g.setColor(getBackground()); 
     g.fillRect(0, 0, getWidth(), getHeight()); 
    } 
    Graphics2D g2d = (Graphics2D) g; 
    // Draw first line 
    g2d.setPaint(topLineColor); 
    g2d.drawLine(0, 0, this.getWidth(), 0); 
    // Draw last line 
    g2d.setPaint(bottomLineColor); 
    g2d.drawLine(0, 23, this.getWidth(), 23); 
    // Draw gradient 
    GradientPaint gradient = new GradientPaint(this.getX(), this.getY() + 1, gradientTop, this.getX(), this.getHeight() - 1, gradientBottom); 
    g2d.setPaint(gradient); 
    g2d.fillRect(this.getX(), this.getY() + 1, this.getWidth(), this.getHeight() - 2); 
    if (titleText != null) 
    { 
     g2d.setFont(new Font("", Font.BOLD, 13)); 
     g2d.setColor(Color.WHITE); 
     g2d.drawString(titleText, 10, 16); 
    } 
} 

Answer 2

在方法paint(Graphics g)，你的第一行是：

super.paintComponent(g); 

這會畫你的按鈕。該方法的其餘部分將繼續繪製該按鈕：

g2d.fillRect(this.getX(), this.getY()+1, this.getWidth(), this.getHeight()-2); 

因此，您看不到任何按鈕。把第一行作爲最後一行，你應該很好。