如何將JPanel添加到不同類的容器中？

Question

基本上我有一個充當容器的類。這是一個JFrame，它的構造函數需要JPanel。現在，我在容器類之外構建了各種JPanel。我有他們設計這種方式的具體原因，主要是與MVC設計模式。

我遇到的問題是，無論何時將JPanel添加到容器，FROM容器類都顯示爲空白。沒有編譯錯誤。我看不出爲什麼它不會添加我要求的內容。我會後一些代碼，這是容器：

public class MainFrame { 

    private JFrame mainContainer = new JFrame("Frog Checkers"); 

    private JPanel frame = new testFrame(); 

    public void start() { 
     mainContainer(frame); 
    } 

    private JFrame mainContainer(JPanel frame) { 
     mainContainer.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     mainContainer.setSize(925, 608); 
     mainContainer.setVisible(true); 
     Dimension dim = Toolkit.getDefaultToolkit().getScreenSize(); 
     mainContainer.setLocation(dim.width/2 - mainContainer.getSize().width 
      /2, dim.height/2 - mainContainer.getSize().height/2); 
     mainContainer.setResizable(false); 

     mainContainer.add(frame); 

     return mainContainer; 
    } 
} 

這就是我想要添加一個JPanel的一個例子：

public class testFrame extends JPanel { 
    private JPanel testPanel = new JPanel() 
    private JButton testButton, anotherButton; 

    public testFrame() { 
     testPanel.setLayout(new GridBagLayout()); 
     GridBagConstraints constraints = new GridBagConstraints(); 

     testButton = new JButton("New Button"); 
     constraints.gridx = 0; // Location on grid 
     constraints.gridy = 3; // Location on grid 
     constraints.gridwidth = 2; // How many grids the width will consume 
     constraints.gridheight = 1; // How many grids the length will consume 
     constraints.weightx = 1.0; // for resizing 
     constraints.weighty = 1.0; // for resizing 
     constraints.anchor = GridBagConstraints.SOUTHWEST; // Where it will be anchored 
     constraints.ipadx = 20; // Internal padding 
     constraints.ipady = 20; // Inernal padding 
     constraints.insets = new Insets(50,50,50,50); 
     testPanel.add(testButton, constraints); 

     anotherButton = new JButton("another Button"); 
     constraints.gridx = 0; // Location on grid 
     constraints.gridy = 3; // Location on grid 
     constraints.gridwidth = 2; // How many grids the width will consume 
     constraints.gridheight = 1; // How many grids the length will consume 
     constraints.weightx = 1.0; // for resizing 
     constraints.weighty = 1.0; // for resizing 
     constraints.anchor = GridBagConstraints.SOUTHWEST; // Where it will be anchored 
     constraints.ipadx = 20; // Internal padding 
     constraints.ipady = 20; // Inernal padding 
     constraints.insets = new Insets(50, 50, 120, 80); 
     testPanel.add(anotherButton, constraints); 
    } 
} 

我使用的GridBagLayout，因爲我被告知無數次不使用空佈局。但如果有人知道使用空佈局的方式，請分享。爲了更清楚一點，所有這些代碼都可以工作，如果我把它作爲容器類中的一個方法，但我不想那樣。任何想法將不勝感激。

Answer 1

問題在於你的testFrame類。它延伸JPanel並在裏面你採取了另一個JPanel這是沒有必要的。如果您堅持要採取，則必須在testFrame的構造函數末尾使用語句add(testPanel);將其添加到testFrame。

類名應以大寫字母開頭。我建議將您的班級重命名爲TestFrame而不是testFrame。

public class testFrame extends JPanel { 
    private JButton testButton, anotherButton; 

    public testFrame() { 
     setLayout(new GridBagLayout()); 
     GridBagConstraints constraints = new GridBagConstraints(); 

     testButton = new JButton("New Button"); 
     constraints.gridx = 0; // Location on grid 
     constraints.gridy = 3; // Location on grid 
     constraints.gridwidth = 2; // How many grids the width will consume 
     constraints.gridheight = 1; // How many grids the length will consume 
     constraints.weightx = 1.0; // for resizing 
     constraints.weighty = 1.0; // for resizing 
     constraints.anchor = GridBagConstraints.SOUTHWEST; // Where it will be anchored 
     constraints.ipadx = 20; // Internal padding 
     constraints.ipady = 20; // Inernal padding 
     constraints.insets = new Insets(50,50,50,50); 
     add(testButton, constraints); 

     anotherButton = new JButton("another Button"); 
     constraints.gridx = 0; // Location on grid 
     constraints.gridy = 3; // Location on grid 
     constraints.gridwidth = 2; // How many grids the width will consume 
     constraints.gridheight = 1; // How many grids the length will consume 
     constraints.weightx = 1.0; // for resizing 
     constraints.weighty = 1.0; // for resizing 
     constraints.anchor = GridBagConstraints.SOUTHWEST; // Where it will be anchored 
     constraints.ipadx = 20; // Internal padding 
     constraints.ipady = 20; // Inernal padding 
     constraints.insets = new Insets(50, 50, 120, 80); 
     add(anotherButton, constraints); 
    } 
} 

而且在MainFrame，使用

getContentPane().add([testFrame object]);

Answer 2

與拉溫德拉同意直接使用JFrame.getContentPane（）是最好的做法。您應該做的另一件事是給ContentPane一個明確的佈局（類似於您對JPanel所做的）。喜歡的東西：

mainContainer.getContentPane().setLayout(new BorderLayout()); 
mainContainer.getContentPane().add(yourPanel, BorderLayout.CENTER); 

你可以選擇任何你想要的佈局，但我經常選擇的BorderLayout我的主框架，因爲中心區域是「貪婪」（不管你放在那裏就會自動嘗試填補空間），這往往是理想的行爲。

其他的事情可能會幫助包括使用GridBagConstraints中的fill屬性來通知它嘗試填充整個面板區域，並覆蓋面板的getPreferredSize()以給佈局一個尺寸提示。