Vaadin Framework - Server-Side Components - ProgressBar
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ProgressBar

Live Demo

The ProgressBar component allows visualizing progress of a task. The progress is specified as a floating-point value between 0.0 and 1.0.

progressbar basic
Figure 1. The ProgressBar component

To display upload progress with the Upload component, you can update the progress bar in a ProgressListener.

When the position of a progress bar is done in a background thread, the change is not shown in the browser immediately. You need to use either polling or server push to update the browser. You can enable polling with setPollInterval() in the current UI instance. See "Server Push" for instructions about using server push. Whichever method you use to update the UI, it is important to lock the user session by modifying the progress bar value inside access() call, as described in "Accessing UI from Another Thread".

ProgressBar bar = new ProgressBar(0.0f);
layout.addComponent(bar);

layout.addComponent(new Button("Increase", click -> {
    float current = bar.getValue();
    if (current < 1.0f)
        bar.setValue(current + 0.10f);
}));

Indeterminate Mode

In the indeterminate mode, a non-progressive indicator is displayed continuously. The indeterminate indicator is a circular wheel in the built-in themes. The progress value has no meaning in the indeterminate mode.

ProgressBar bar = new ProgressBar();
bar.setIndeterminate(true);
progressbar indeterminate
Figure 2. Indeterminate progress bar

Doing Heavy Computation

The progress bar is typically used to display the progress of a heavy server-side computation task, often running in a background thread. The UI, including the progress bar, can be updated either with polling or by using server push. When doing so, you must ensure thread-safety, most easily by updating the UI inside a UI.access() call in a Runnable, as described in "Accessing UI from Another Thread".

CSS Style Rules

.v-progressbar, v-progressbar-indeterminate {}
  .v-progressbar-wrapper {}
    .v-progressbar-indicator {}

The progress bar has a v-progressbar base style. The progress is an element with v-progressbar-indicator style inside the wrapper, and therefore displayed on top of it. When the progress element grows, it covers more and more of the animated background.

The progress bar can be animated (some themes use that). Animation is done in the element with the v-progressbar-wrapper style, by having an animated GIF as the background image.

In the indeterminate mode, the top element also has the v-progressbar-indeterminate style. The built-in themes simply display the animated GIF in the top element and have the inner elements disabled.