使用可运行程序时，为什么Java SWT Gui应用程序的标签未更改？

Question

So I am having a problem at the moment because the everything is working properly and just been experimenting with some code to create a easy system time and date setup. I have one problem that I somehow can't seem to fix. So I have identified a label (not a JLabel) and when I try to run it via a runnable void it seems to error when I try to set the text to update the exact time of the system. So example Time.setText(time); time will be identified as a string but it simply errors and doesn't work.

import java.util.Calendar;
import java.util.GregorianCalendar;

import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Label;
import org.eclipse.swt.SWT;
import org.eclipse.swt.widgets.Composite;

public class HomeScreen {

protected Shell shell;
private Label Date;
private Label Time;
private Composite composite;


/**
 * Launch the application.
 * @param args
 */
public static void main(String[] args) {
            try {
                HomeScreen window = new HomeScreen();
                window.open();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

/**
 * Open the window.
 */
public void open() {
    Display display = Display.getDefault();
    createContents();
    shell.open();
    shell.layout();
    Date();
    Time();
    while (!shell.isDisposed()) {
        if (!display.readAndDispatch()) {
            display.sleep();
        }
    }
}

/**
 * Create contents of the window.
 */
protected void createContents() {
    shell = new Shell();
    shell.setSize(450, 300);
    shell.setText("Project Serenity");

    composite = new Composite(shell, SWT.NONE);
    composite.setBounds(0, 0, 470, 278);

    Time = new Label(composite, SWT.NONE);
    Time.setLocation(10, 192);
    Time.setSize(169, 31);
    Time.setText("Time");

    Date = new Label(composite, SWT.NONE);
    Date.setLocation(10, 217);
    Date.setSize(169, 38);
    Date.setText("Date");

}
public void Date() 
{
    Thread Date2 = new Thread()
    {
        @Override
        public void run()
        {   
            try {
                for(;;){
                    Calendar cal = new GregorianCalendar();
                    int day = cal.get(Calendar.DAY_OF_MONTH);
                    int month = cal.get(Calendar.MONTH);
                    int year = cal.get(Calendar.YEAR);
                    Time.setText(day + ", " + month + " " + year);          
                sleep(1000);
                }
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    };
    Date2.start();
}
public void Time() 
{
    Thread Time2 = new Thread()
    {
        @Override
        public void run()
        {
            try {
                for(;;){
                Calendar cal = new GregorianCalendar();
                int second = cal.get(Calendar.SECOND);
                int minute = cal.get(Calendar.MINUTE);
                int hour = cal.get(Calendar.HOUR);
                int am_pm = cal.get(Calendar.AM_PM);
                sleep(1000);
                Time.setText(hour + ":" + minute + ":" + second + " " + am_pm);
                }
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    };
    Time2.start();
}

}

Thx Pixl

Answer 1

All access to User Interface objects must be done in the User Interface thread. Attempting to access them in any other thread will throw an exception.

You can use the asyncExec method of Display to execute a Runnable in the UI thread. So instead of just doing:

Time.setText(day + ", " + month + " " + year);          

in your background thread do:

Display.getDefault().asyncExec(() -> Time.setText(day + ", " + month + " " + year));

The above is for Java 8, if you are using an older version of Java use:

Display.getDefault().asyncExec(new Runnable() {
  @Override
  public void run {
    Time.setText(day + ", " + month + " " + year);          
  }
});

Note: Please learn to use the Java naming conventions - variables start with a lower case letter so Time should be time .

You also are not doing anything to stop your update threads when you exit the application. Accessing controls once the main UI thread has stopped will give you an error. You can test if the Time control has been disposed which will tell you that the application has stopped.

if (Time.isDisposed()) {
  // TODO exit the thread
}