我的程序有三个功能（退出除外）：读取文件，在文件中搜索并写入文件。我有一个完整的功能作为控制台应用程序，我正在为它的GUI（Swing）工作。我有一个主窗口，其中创建了所有组件并且功能正常（按钮单击 - ＆gt;通过控制台运行）。我之后现在完全切断了t =我对控制台的需求。
我正在处理Read函数的这个更改（目前），所以我可以让它正常工作。我遇到的问题是用户无法在JTextField＆amp;内部指定所需的文件（类型路径）。在获取值（null）并将其分配给文件变量之前，单击与所需函数对应的buttonn。
这是包含所有内容的类，除了包含特定函数的类，我通过main链接到它：
public class SimpleDBGUI{
static File targetFile; //Declare File var to be used in methods below for holding user's desired file
public void mainWindow(){
//Create main window for Program
JFrame mainWindow = new JFrame("Simple Data Base"); //Init frame
mainWindow.setSize(500, 180); //Set frame size
mainWindow.setVisible(true); //Make frame visible
//Create panel for the main window of the GUI
JPanel simpleGUI = new JPanel( new GridBagLayout());
GridBagConstraints gbCons = new GridBagConstraints();
mainWindow.getContentPane().add(simpleGUI); //Adds JPanel container to the ContentPane of the JFrame
//Create button linking to read function
JButton readButton = new JButton("Read"); //Init button, and give text
gbCons.fill = GridBagConstraints.BOTH;
gbCons.gridx = 0;
gbCons.gridy = 2;
gbCons.weightx = .1;
readButton.setActionCommand("Read");
readButton.addActionListener( new ButtonClickListener());
simpleGUI.add(readButton, gbCons); //Adds the "Read" button to the JPanel
//Create button linking to the search function
JButton searchButton = new JButton("Search"); //Init button with text
gbCons.fill = GridBagConstraints.BOTH;
gbCons.gridx = 1;
gbCons.gridy = 2;
gbCons.weightx = .1;
searchButton.setActionCommand("Search");
searchButton.addActionListener( new ButtonClickListener());
simpleGUI.add(searchButton, gbCons); //Adds the "Search" button to the JPanel
//Create button linking to the write function
JButton writeButton = new JButton("Write"); //Init button with text
gbCons.fill = GridBagConstraints.BOTH;
gbCons.gridx = 2;
gbCons.gridy = 2;
gbCons.weightx = .1;
writeButton.setActionCommand("Write");
writeButton.addActionListener( new ButtonClickListener());
simpleGUI.add(writeButton, gbCons); //Adds the "Write" button to the JPanel
//Create label prompting user to specify desired function
JLabel promptText = new JLabel("Click 'Read' to read a file, 'Search' to search within a file, 'Write' to write to a file:"); //Give user a prompt to select desired function
gbCons.fill = GridBagConstraints.BOTH;
gbCons.gridx = 0;
gbCons.gridy = 0;
gbCons.gridwidth = 3;
simpleGUI.add(promptText, gbCons); //Add prompt to the JPanel
//Create button to exit program
JButton exitButton = new JButton("Exit");
gbCons.fill = GridBagConstraints.BOTH;
gbCons.gridx = 0;
gbCons.gridy = 3;
gbCons.gridwidth = 3;
exitButton.setActionCommand("Exit");
exitButton.addActionListener( new ButtonClickListener());
simpleGUI.add(exitButton, gbCons); //Add "Exit" button to the JPanel
//Create TextField for user to input a desired file
JTextField sdbTarget = new JTextField();
gbCons.fill = GridBagConstraints.BOTH;
gbCons.gridx = 0;
gbCons.gridy = 1;
gbCons.gridwidth = 3;
simpleGUI.add(sdbTarget, gbCons); //Adds TextField to GUI
targetFile = new File(sdbTarget.getText()); //Writes input string to a File var, works but out of time resulting in null value
}
public class ButtonClickListener implements ActionListener{ //Sets the EventListener for every function
public void actionPerformed(ActionEvent event){
//targetFile = File(sdbTarget.getText()); //Was a proposed solution, but kept giving type resolving errors
try{ //Leftovers from the console version of the app,
Scanner inputChoice = new Scanner(System.in); //these were left so my Search and Write functions would still work in the console
File file = new File("C:/Users/Joshua/Desktop/jOutFiles/SimpleDB.txt"); //
FileWriter writer = new FileWriter(file, true); //
String function = event.getActionCommand();
//Reads the ActionCommand into a string for use in performing desired function
if( function.equals("Read")){ //Read function
Desktop desktop = Desktop.getDesktop(); //For the GUI version, supposed to open "targetFile" upon readButtonClick
desktop.open(targetFile); //
// SimpleDBReader sdbrObject = new SimpleDBReader(); //Bit left from console version, still functional
// sdbrObject.sdbReader(inputChoice, file); //
}else if( function.equals("Search")){ //Search Function
SimpleDBSearch sdbsObject = new SimpleDBSearch();
sdbsObject.sdbSearch(inputChoice, writer, file);
}else if( function.equals("Write")){ //Write function
SimpleDBWriter sdbwObject = new SimpleDBWriter();
sdbwObject.sdbWriter(inputChoice, file);
}else if( function.equals("Exit")){
System.exit(0);
}
}catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
答案 0 :(得分：3)
targetFile = new File(sdbTarget.getText());
但是sdbTarget尚未应用任何值。
但更好的解决方案是使用您的ActionListener，ButtonClickListener来检查值
String target = sdbTarget.getText();
if (target != null && !target.trim().isEmpty()) {
File targetFile = new File(target)
String function = event.getActionCommand(); //Reads the ActionCommand into a string for use in performing desired function
if (function.equals("Read")) { //Read function
Desktop desktop = Desktop.getDesktop(); //For the GUI version, supposed to open "targetFile" upon readButtonClick
desktop.open(targetFile);
//...
这样，每次调用targetFile时，您始终会评估actionPerformed