Vaadin Web应用开发教程(24):UI组件-ProgressIndicator组件

ProgressIndicator组件显示进程条，ProgressIndicator组件定时向服务器查询其当前值，如果值有变化，则更新进程条进度。Web应用本身无需实现任何查询服务器的操作，查询由ProgressIndicator组件自动完成。
ProgressIndicator组件的值域为0.0到1.0之间。缺省的查询(polling)间隔为1秒，可以使用setPollingInterval 修改。

 // Create the indicator
 final ProgressIndicator indicator =
         new ProgressIndicator(new Float(0.0));
 main.addComponent(indicator);

 // Set polling frequency to 0.5 seconds.
 indicator.setPollingInterval(500);

 

ProgressIndicator组件通常用来显示一些耗时操作（比如下载文件）的进度。 使用setValue 为ProgressIndicator组件设置当前值。
下面代码模拟一个费时操作提供ProgressIndicator组件显示进度。

 // Create an indicator that makes you look busy
 final ProgressIndicator indicator =
         new ProgressIndicator(new Float(0.0));
 main.addComponent(indicator);

 // Set polling frequency to 0.5 seconds.
 indicator.setPollingInterval(500);

 // Add a button to start working
 final Button button = new Button("Click to start");
 main.addComponent(button);

 // Another thread to do some work
 class WorkThread extends Thread {
     public void run () {
         double current = 0.0;
         while (true) {
             // Do some "heavy work"
             try {
                 sleep(50); // Sleep for 50 milliseconds
             } catch (InterruptedException e) {}

             // Show that you have made some progress:
             // grow the progress value until it reaches 1.0.
             current += 0.01;
             if (current>1.0)
                 indicator.setValue(new Float(1.0));
             else
                 indicator.setValue(new Float(current));

             // After all the "work" has been done for a while,
             // take a break.
             if (current > 1.2) {
                 // Restore the state to initial.
                 indicator.setValue(new Float(0.0));
                 button.setVisible(true);
                 break;
             }
         }
     }
 }

 // Clicking the button creates and runs a work thread
 button.addListener(new Button.ClickListener() {
     public void buttonClick(ClickEvent event) {
         final WorkThread thread = new WorkThread();
         thread.start();

         // The button hides until the work is done.
         button.setVisible(false);
     }
 });