Keylistener可以工作，但並未執行預期的操作。爲什麼？

Question

這是創建一個Frame並保存實現Graphics的類的MainApplication。

MainApplication.java

import java.awt.*; 

public class MainApplication 
{ 
    public MainApplication() 
    { 
     Frame frame= new Frame("Test App"); 
     frame.add(new KeyTest()); 
     frame.setBackground(Color.RED); 
     frame.setLayout(null); 
     frame.setSize(700,750); 
     frame.setVisible(true); 
    } 
    public static void main(String args[]) 
    { 

     new MainApplication(); 

    } 
} 

此類創建所有的圖形形狀，也實現了KeyListener的。

KeyTest.java

import java.awt.BasicStroke; 
import java.awt.Canvas; 
import java.awt.Color; 
import java.awt.Font; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.RenderingHints; 
import java.awt.Shape; 
import java.awt.Stroke; 
import java.awt.event.KeyEvent; 
import java.awt.event.KeyListener; 
import java.awt.geom.RoundRectangle2D; 

public class KeyTest extends Canvas { 


    /** 
    * 
    */ 
    private static final long serialVersionUID = 3L; 
    Graphics2D graphics2D; 
    Color color = Color.BLACK; 
    private static float borderThickness = 5; 
    Shape firstShape = new RoundRectangle2D.Double(20,40,300,50,10,10); 
    Shape secondShape = new RoundRectangle2D.Double(20,150,300,50,10,10); 
    public KeyTest() 
    { 
     setBackground(Color.RED); 
     setSize(700,750);    
    } 
    public void paint(Graphics graphics) 
    { 

     graphics2D = (Graphics2D)graphics; //TypeCasting to 2D 
     System.out.println("I am inside paint"); 

     //  Smoothening the corners 
     graphics2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING, 
       RenderingHints.VALUE_ANTIALIAS_ON); 

     //  Apple border color 
     Stroke oldStroke = graphics2D.getStroke(); 
     graphics2D.setStroke(new BasicStroke(borderThickness)); 
     graphics2D.setColor(Color.WHITE); 

     //  Drawing a RoundedRectangle for Apple  
     graphics2D.draw(firstShape); 
     graphics2D.setStroke(oldStroke); 

     //  Setting the Background Color 
     graphics2D.setColor(Color.BLACK); 
     graphics2D.fill(firstShape); 


     //  Setting the font inside the shape 
     Font firstFont = new Font("Serif", Font.BOLD,35); 
     graphics2D.setFont(firstFont); 
     graphics2D.setColor(Color.WHITE); 
     graphics2D.drawString("Apple",30,80); 


     //  Pineapple border color 
     graphics2D.setStroke(new BasicStroke(borderThickness)); 
     graphics2D.setColor(Color.WHITE); 

     //  Drawing a RoundedRectangle for Pineapple  
     graphics2D.draw(secondShape); 
     graphics2D.setStroke(oldStroke); 

     //  Setting the Background Color 
     graphics2D.setColor(Color.BLACK); 
     graphics2D.fill(secondShape); 

     //  Setting the font inside the shape 
     Font secondFont = new Font("Serif", Font.BOLD,35); 
     graphics2D.setFont(secondFont); 
     graphics2D.setColor(Color.WHITE); 
     graphics2D.drawString("Pineapple",30,190); 

     addKeyListener(new KeyListener(){ 

      @Override 
      public void keyTyped(KeyEvent e) { 
       // TODO Auto-generated method stub 

      } 

      @Override 
      public void keyPressed(KeyEvent e) { 
       int keyCode = e.getKeyCode(); 

       System.out.println(keyCode); 
       System.out.println(KeyEvent.VK_UP); 
       if(keyCode==KeyEvent.VK_UP){ 
        System.out.println("Going to move up"); 
        move(firstShape); 

       } 
       if(keyCode==KeyEvent.VK_DOWN){ 
        System.out.println("Going to move down"); 
        move(secondShape); 

       } 
      } 

      @Override 
      public void keyReleased(KeyEvent e) { 
       // TODO Auto-generated method stub 

      }}); 
    } 
    public void move(Shape s){ 

     System.out.println("Check:"+s.getBounds2D()); 
     graphics2D.setColor(Color.GREEN); 
     graphics2D.fill(s); 
     System.out.println("moving out"); 
    } 
} 

我的控制檯輸出清楚地表明，我的主要作品監聽器，但其不執行，我想讓它做任務。

控制檯輸出

我裏面的油漆要拉昇

檢查：java.awt.geom.Rectangle2D中$雙[X = 20.0，Y = 40.0，W = 300.0，H = 50.0]

移出要向下移動

檢查：java.awt.geom.Rectangle2D中$雙[X = 20.0，Y = 150.0，W = 300。 0，H = 50.0]

移出

OUTPUT：

現在正在逐漸輸出..（IMAGE 1）

我期望當我按下向下箭頭按鈕的輸出（圖像2）

我期望當我按下上箭頭按鈕的輸出（圖像3）

Answer 1

首先，您不應該在paint方法中添加KeyListener，因爲每次調用paint時它都會註冊一個附加值。

然後，不依賴於存儲在其上的Component和繪畫的東西Graphics對象，因爲很多東西可以是你無法控制的外部（例如它可以通過其他發生的歷史AWT UI操作得到清除何去何從呢）。

唯一相關的Graphics對象是您在paint中收到的實例，且僅在paint方法的範圍內。

所以在下面的代碼：

• addKeyListener已被移動的paint之外。
• 關鍵收聽者 調用move，其中Shape的索引將移動。
• move方法 現在只註冊Shape高亮取決於收到的索引，並呼籲repaint。
• Graphics2D對象被設置爲局部變量爲paint，因爲它與 不相關。
• paintHighlightedShape是負責繪製高亮Shape，在Graphics2D對象作爲參數
• 的paint方法現在調用paintHighlightedShape與作爲參數傳遞其Graphics2D對象接收。

注意，一個main方法已經被添加到KeyTest用於測試目的，它的內容應該在你的主類。

此外，如果您計劃讓更多形狀突出顯示，您可以使用Shape的數組，並且傳遞給move的索引可以是要突出顯示的Shape的數組索引。

最後，爲了優化，我們不應該畫出規則的形狀，如果它是突出顯示的形狀，因爲無論如何都會被綠色形狀隱藏。 考慮創建一個drawShape(Graphics2D, Shape)方法，該方法將繪製規則形狀或綠色形狀，具體取決於要突出顯示的形狀。 您可以從paint方法中調用此方法，在所有形狀上循環。

import java.awt.BasicStroke; 
import java.awt.Canvas; 
import java.awt.Color; 
import java.awt.Font; 
import java.awt.Frame; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.RenderingHints; 
import java.awt.Shape; 
import java.awt.Stroke; 
import java.awt.event.KeyEvent; 
import java.awt.event.KeyListener; 
import java.awt.geom.RoundRectangle2D; 

public class KeyTest extends Canvas { 

    /** 
    * 
    */ 
    private static final long serialVersionUID = 3L; 
    Color color = Color.BLACK; 
    private static float borderThickness = 5; 
    Shape firstShape = new RoundRectangle2D.Double(20, 40, 300, 50, 10, 10); 
    Shape secondShape = new RoundRectangle2D.Double(20, 150, 300, 50, 10, 10); 

    Shape highlightedShape; 

    public KeyTest() { 
     setBackground(Color.RED); 
     setSize(700, 750); 
    } 

    public static void main(final String[] args) { 
     Frame frame = new Frame("Test App"); 
     final KeyTest keyTest = new KeyTest(); 
     keyTest.addKeyListener(new KeyListener() { 

      @Override 
      public void keyTyped(final KeyEvent e) { 
       // TODO Auto-generated method stub 

      } 

      @Override 
      public void keyPressed(final KeyEvent e) { 
       int keyCode = e.getKeyCode(); 

       System.out.println(keyCode); 
       System.out.println(KeyEvent.VK_UP); 
       if (keyCode == KeyEvent.VK_UP) { 
        System.out.println("Going to move up"); 
        keyTest.move(1); 

       } 
       if (keyCode == KeyEvent.VK_DOWN) { 
        System.out.println("Going to move down"); 
        keyTest.move(2); 

       } 
      } 

      @Override 
      public void keyReleased(final KeyEvent e) { 
       // TODO Auto-generated method stub 

      } 
     }); 
     frame.add(keyTest); 
     frame.setBackground(Color.RED); 
     frame.setLayout(null); 
     frame.setSize(700, 750); 
     frame.setVisible(true); 
    } 

    public void paint(final Graphics graphics) { 

     Graphics2D graphics2D = (Graphics2D) graphics; //TypeCasting to 2D 
     System.out.println("I am inside paint"); 

     //  Smoothening the corners 
     graphics2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING, 
       RenderingHints.VALUE_ANTIALIAS_ON); 

     //  Apple border color 
     Stroke oldStroke = graphics2D.getStroke(); 
     graphics2D.setStroke(new BasicStroke(borderThickness)); 
     graphics2D.setColor(Color.WHITE); 

     //  Drawing a RoundedRectangle for Apple 
     graphics2D.draw(firstShape); 
     graphics2D.setStroke(oldStroke); 

     //  Setting the Background Color 
     graphics2D.setColor(Color.BLACK); 
     graphics2D.fill(firstShape); 

     //  Setting the font inside the shape 
     Font firstFont = new Font("Serif", Font.BOLD, 35); 
     graphics2D.setFont(firstFont); 
     graphics2D.setColor(Color.WHITE); 
     graphics2D.drawString("Apple", 30, 80); 

     //  Pineapple border color 
     graphics2D.setStroke(new BasicStroke(borderThickness)); 
     graphics2D.setColor(Color.WHITE); 

     //  Drawing a RoundedRectangle for Pineapple 
     graphics2D.draw(secondShape); 
     graphics2D.setStroke(oldStroke); 

     //  Setting the Background Color 
     graphics2D.setColor(Color.BLACK); 
     graphics2D.fill(secondShape); 

     //  Setting the font inside the shape 
     Font secondFont = new Font("Serif", Font.BOLD, 35); 
     graphics2D.setFont(secondFont); 
     graphics2D.setColor(Color.WHITE); 
     graphics2D.drawString("Pineapple", 30, 190); 

     paintHighlightedShape(graphics2D); 

    } 

    private void paintHighlightedShape(final Graphics2D graphics2D) { 

     if (highlightedShape != null) { 

      graphics2D.setColor(Color.GREEN); 
      graphics2D.fill(highlightedShape); 

     } 
    } 

    public void move(final int shapeNumber) { 

     switch (shapeNumber) { 
     case 1: 
      highlightedShape = firstShape; 
      break; 
     case 2: 
      highlightedShape = secondShape; 
      break; 
     default: 

     } 

     System.out.println("Check:" + highlightedShape.getBounds2D()); 
     System.out.println("Moving shape : " + highlightedShape); 
     repaint(); 

     System.out.println("moving out"); 

    } 
}