使用线程循环更新JFrame [英] Using a thread loop to update a JFrame
问题描述
我对在循环中使用线程进行了广泛的搜索，虽然我理解了线程是如何工作的这一概念，但我仍然似乎无法掌握如何在我的简单应用程序中实现它.
我的应用程序由带有文本框的表单组成.一旦循环迭代，则需要更新此文本框.它从按下一个按钮开始，但是循环也应该从按下一个停止按钮结束. Ive使用布尔值来跟踪是否按下了该值.
这是我的表单代码:
package threadtester;
public class MainForm extends javax.swing.JFrame {
public MainForm() {
initComponents();
}
private void RunButtonActionPerformed(java.awt.event.ActionEvent evt) {
ThreadTester.setRunnable(true);
ThreadTester example = new ThreadTester(2,this);
example.run();
}
private void StopButtonActionPerformed(java.awt.event.ActionEvent evt) {
ThreadTester.setRunnable(false);
}
public static void main(String args[]) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new MainForm().setVisible(true);
}
});
}
public void setTextBox(String myString){
MainTextbox.setText(myString);
}
}
您可以看到我按下了一个按钮.当按下按钮时，这将执行另一个名为ThreadTester的类中的代码.这是该类的代码:
package threadtester;
import java.util.logging.Level;
import java.util.logging.Logger;
public class ThreadTester implements Runnable
{
int thisThread;
MainForm myMainForm;
private static boolean runnable;
// constructor
public ThreadTester (int number,MainForm mainForm)
{
thisThread = number;
myMainForm = mainForm;
}
public void run ()
{
for (int i =0;i< 20; i++) {
if(runnable==false){
break;
}
System.out.println("I'm in thread " + thisThread + " line " + i);
myMainForm.setTextBox(i + "counter");
try {
Thread.sleep(1000);
} catch (InterruptedException ex) {
Logger.getLogger(ThreadTester.class.getName()).log(Level.SEVERE, null, ex);
}
} }
public static void setRunnable(Boolean myValue){
runnable = myValue;
}
public static void main(String[] args) {
MainForm.main(args);
}
}
如您所见，循环是在单独的线程上创建的...但是文本框仅在循环完成后才更新.现在，据我在MainForm中知道的那样，我创建了一个单独的线程来运行循环，所以我不明白为什么它没有运行?我会尝试查看有关堆栈交换的示例，但是我似乎无法使它们适应我的要求.
有了塔索斯的建议，我的运行方法现在看起来像这样:
public void run ()
{
for (int i =0;i< 20; i++) {
if(runnable==false){
break;
}
System.out.println("I'm in thread " + thisThread + " line " + i);
final String var = i + "counter";
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
myMainForm.setTextBox(var);
}
});
try {
Thread.sleep(1000);
} catch (InterruptedException ex) {
Logger.getLogger(ThreadTester.class.getName()).log(Level.SEVERE, null, ex);
}
} }
为使Tassos的答案生效，您实际上必须创建一个新线程，而您没有这样做.只需致电
ThreadTester example = new ThreadTester(2,this);
example.run();
还不够，只是从EDT调用run方法.您需要执行以下操作:
Thread t = new Thread(new ThreadTester(2,this));
t.start();
请参考定义和启动线程. /p>
此外，您还希望从两个不同的线程(runnable)修改同一字段，这是一个错误.您应该阅读有关Java并发的更多信息.
ive done some extensive searching on using threads in a loop and whilst I understand the concept how how seperate threads work, I still cant seem to grasp how to implement it in my simple application.
My application consists of a form with a text box. This textbox needs to be updated once ever iteration of a loop. It starts with the press of a button but the loop should also finish with the press of a stop button. Ive used a boolean value to track if its been pressed.
Here is my form code:
package threadtester;
public class MainForm extends javax.swing.JFrame {
public MainForm() {
initComponents();
}
private void RunButtonActionPerformed(java.awt.event.ActionEvent evt) {
ThreadTester.setRunnable(true);
ThreadTester example = new ThreadTester(2,this);
example.run();
}
private void StopButtonActionPerformed(java.awt.event.ActionEvent evt) {
ThreadTester.setRunnable(false);
}
public static void main(String args[]) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new MainForm().setVisible(true);
}
});
}
public void setTextBox(String myString){
MainTextbox.setText(myString);
}
}
As you can see I have a button that is pressed. When the button is pressed this executes the code thats in a different class called ThreadTester. Here is the code for that class:
package threadtester;
import java.util.logging.Level;
import java.util.logging.Logger;
public class ThreadTester implements Runnable
{
int thisThread;
MainForm myMainForm;
private static boolean runnable;
// constructor
public ThreadTester (int number,MainForm mainForm)
{
thisThread = number;
myMainForm = mainForm;
}
public void run ()
{
for (int i =0;i< 20; i++) {
if(runnable==false){
break;
}
System.out.println("I'm in thread " + thisThread + " line " + i);
myMainForm.setTextBox(i + "counter");
try {
Thread.sleep(1000);
} catch (InterruptedException ex) {
Logger.getLogger(ThreadTester.class.getName()).log(Level.SEVERE, null, ex);
}
} }
public static void setRunnable(Boolean myValue){
runnable = myValue;
}
public static void main(String[] args) {
MainForm.main(args);
}
}
as you can see the loop has been created on a seperate thread... but the textbox only updates after the loop has finished. Now as far as im aware in my MainForm I created a seperate thread to run the loop on, so I dont understand why its not running? Any guidence would be much appreciated, ive tried looking at examples on stack exchange but I cant seem to get them to fit into my implemntation.
With the recommendation suggested by Tassos my run method now looks like this:
public void run ()
{
for (int i =0;i< 20; i++) {
if(runnable==false){
break;
}
System.out.println("I'm in thread " + thisThread + " line " + i);
final String var = i + "counter";
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
myMainForm.setTextBox(var);
}
});
try {
Thread.sleep(1000);
} catch (InterruptedException ex) {
Logger.getLogger(ThreadTester.class.getName()).log(Level.SEVERE, null, ex);
}
} }
In order for Tassos' answer to work, you actually have to create an new thread, which you did not do. Simply calling
ThreadTester example = new ThreadTester(2,this);
example.run();
is not enough, sice that just calls the run method from EDT. You need to do the following:
Thread t = new Thread(new ThreadTester(2,this));
t.start();
Please refer to Defining and Starting a Thread.
Also, you want modify the same field from two different threads (runnable), which is a bug. You should read more about java concurrency.
这篇关于使用线程循环更新JFrame的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
