Ich möchte ein Kombinationsfeld erstellen, wenn ich jedes Mal auf eine Schaltfläche klicke

Question

Dies ist mein Klickereignis. Ich möchte Kombinationsfelder jedes Mal erstellen, wenn ich auf die Schaltfläche klicke.

private void jButton1ActionPerformed (java.awt.event.ActionEvent evt) {

jButton1.addActionListener(new ActionListener(){ 

    @Override 
    public void actionPerformed(ActionEvent evt){ 

    List<JComboBox> listOfComboBoxes = new ArrayList<JComboBox>(); 

for(int i=1;i<4;i++){ 
      int x = 28; 
      int y = 100; 
      int a = 145; 
      int b = 28; 

      listOfComboBoxes.get(i); 
     listOfComboBoxes.get(i).addItem("--Select the Teacher--"); 
     listOfComboBoxes.get(i).setLayout(null); 
     listOfComboBoxes.get(i).setLocation(x,y); 

      add(listOfComboBoxes.get(i)).setSize(a,b); 
     x=x+30; 
    a=a+40; 

    i++; 

    } 
    } 

});

Answer 1

Sie sind mit zwei Problemen fertig: Eins fügt Combos hinzu (sagen wir zu einem JPanel), und das zweite ist das Auslegen dieser Combos. Lassen Sie uns brechen sie in zwei, und verstehen, die das Hinzufügen Mechanismus zuerst:

import java.awt.BorderLayout; 
import java.awt.Dimension; 
import java.awt.event.ActionEvent; 
import java.util.ArrayList; 
import java.util.List; 

import javax.swing.BoxLayout; 
import javax.swing.JButton; 
import javax.swing.JComboBox; 
import javax.swing.JFrame; 
import javax.swing.JPanel; 

public class MakeCombos extends JFrame { 

    private static final int Number_OF_COMBOS = 4; 
    private JButton jButton1; 
    List<JComboBox> listOfComboBoxes; 
    private JPanel panel; 
    int counter = 0; 

    MakeCombos(){ 

     super("Test frame"); 
     setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); 
     setPreferredSize(new Dimension(400,300)); 
     setLocationRelativeTo(null); 
     getContentPane().setLayout(new BoxLayout(getContentPane(), BoxLayout.Y_AXIS)); 

     //create a panel 
     panel = new JPanel(); 
     getContentPane().add(panel); 

     //add button to it 
     jButton1 = new JButton("Click Me"); 
     //add action listener to the panel 
     jButton1.addActionListener((ActionEvent e)-> { 
      jButton1ActionPerformed(); 
     }); 
     panel.add(jButton1, BorderLayout.CENTER); 

     validate(); 
     pack(); 
     setVisible(true); 

     listOfComboBoxes = makeCombos(); 
    } 

    /** 
    *@return 
    */ 
    private List<JComboBox> makeCombos() { 

     List combos = new ArrayList<JComboBox>(); 

     for(int i = 0; i < Number_OF_COMBOS; i++) { 

      JComboBox<String> combo = new JComboBox<>(new String[] {}); 
      combos.add(combo); 
     } 
     return combos; 
    } 

    private void jButton1ActionPerformed() { 

     if(counter >= listOfComboBoxes.size()) { 
      return; 
     } 


     listOfComboBoxes.get(counter); 
     listOfComboBoxes.get(counter).addItem("--Select the Teacher--"); 
     getContentPane().add(listOfComboBoxes.get(counter)) ;//.setSize(a,b); 

     counter++; 

     pack(); 

    } 

    public static void main(String[] args) { 

     new MakeCombos(); 
    } 

} 

Run es, und wenn es nicht klar ist, zögern Sie nicht zu fragen.
Jetzt gehen wir noch einen Schritt weiter und machen auch das Layout. siehe Kommentare:

import java.awt.BorderLayout; 
import java.awt.Dimension; 
import java.awt.event.ActionEvent; 
import java.util.ArrayList; 
import java.util.List; 

import javax.swing.JButton; 
import javax.swing.JComboBox; 
import javax.swing.JFrame; 
import javax.swing.JPanel; 

public class MakeCombos extends JFrame { 

    private static final int Number_OF_COMBOS = 4; 
    private List<JComboBox<String>> listOfComboBoxes; 

    private JPanel combosPanel; 

    private int xPosition = 28; 
    private int yPosition = 100; 
    private int width = 145; 
    private int height = 28; 
    private  int counter = 0; 

    MakeCombos(){ 

     //make width frame for testing 
     super("Test frame"); 
     setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); 
     setPreferredSize(new Dimension(500,400)); 
     setLocationRelativeTo(null); 
     //set layout manager to the frame 
     getContentPane().setLayout(new BorderLayout()); 

     //add panel + button to the frame 
     JPanel buttonPanel = new JPanel(); 
     getContentPane().add(buttonPanel, BorderLayout.NORTH); //add the panel to the frame 

     //add button to the button panel 
     JButton jButton1 = new JButton("Click Me"); 
     //add action listener to the button 
     jButton1.addActionListener((ActionEvent e)-> { 
      jButton1ActionPerformed(); 
     }); 
     buttonPanel.add(jButton1, BorderLayout.CENTER); 

     //--add width panel for the combos 
     combosPanel = new JPanel(); 
     //set layout manager to null so you can layout each combo 
     //consider using a layout manager instead 
     combosPanel.setLayout(null); 
     getContentPane().add(combosPanel, BorderLayout.CENTER); //add the panel to the frame 

     validate(); 
     pack(); 
     setVisible(true); 

     //make the combos and add them to width list 
     listOfComboBoxes = makeCombos(); 
    } 

    /** 
    * 
    */ 
    private List<JComboBox<String>> makeCombos() { 

     List<JComboBox<String>> combos = new ArrayList<JComboBox<String>>(); 

     for(int i = 0; i < Number_OF_COMBOS; i++) { 

      JComboBox<String> combo = new JComboBox<>(new String[] {}); 
      combos.add(combo); 
     } 
     return combos; 
    } 

    private void jButton1ActionPerformed() { 

     if(counter >= listOfComboBoxes.size()) { 
      return; 
     } 

     ////////////////////////////////////////////////////////////////////////////// 
     //////////////// note : all this block could be moved to MakeCombos() //////// 
     // (adding content and setting bounds could have been done when creating //// 
     //the combo 

     //add content to the combo 
     listOfComboBoxes.get(counter).addItem("--Select the Teacher--"); 

     //set layout bounds to each combo 
     listOfComboBoxes.get(counter).setBounds(xPosition, yPosition, width, height); 

     //increment position 
     xPosition=xPosition+30; 
     yPosition=yPosition+40; 

     //////////////////////////////////////////////////////////////////////////// 
     /////////////////////// end of move-to-makeCombos() block ////////////////// 
     //////////////////////////////////////////////////////////////////////////// 

     //add the combo to the combos panel 
     combosPanel.add(listOfComboBoxes.get(counter)) ; 

     //increment position and counter 
     counter++; 

     repaint(); 
     pack(); 

    } 

    public static void main(String[] args) { 

     new MakeCombos(); 
    } 
}