How to start a file download in vaadin without button?

Question

I know that it is really easy to create a FileDownloader and call extend with a Button. But how do I start a download without the Button?

Answer 1

I found a solution myself. Actually two. The first one uses the deprecated method Page.open()

public class DownloadComponent extends CustomComponent implements ValueChangeListener {
private ComboBox cb = new ComboBox();

public DownloadComponent() {
    cb.addValueChangeListener(this);
    cb.setNewItemsAllowed(true);
    cb.setImmediate(true);
    cb.setNullSelectionAllowed(false);
    setCompositionRoot(cb);
}

@Override
public void valueChange(ValueChangeEvent event) {
    String val = (String) event.getProperty().getValue();
    FileResource res = new FileResource(new File(val));
    Page.getCurrent().open(res, null, false);
}
}

The javadoc here mentions some memory and security problems as reason for marking it deprecated

---

In the second I try to go around this deprecated method by registering the resource in the DownloadComponent. I'd be glad if a vaadin expert comments this solution.

public class DownloadComponent extends CustomComponent implements ValueChangeListener {
private ComboBox cb = new ComboBox();
private static final String MYKEY = "download";

public DownloadComponent() {
    cb.addValueChangeListener(this);
    cb.setNewItemsAllowed(true);
    cb.setImmediate(true);
    cb.setNullSelectionAllowed(false);
    setCompositionRoot(cb);
}

@Override
public void valueChange(ValueChangeEvent event) {
    String val = (String) event.getProperty().getValue();
    FileResource res = new FileResource(new File(val));
    setResource(MYKEY, res);
    ResourceReference rr = ResourceReference.create(res, this, MYKEY);
    Page.getCurrent().open(rr.getURL(), null);
}
}

Note: I do not really allow the user to open all my files on the server and you should not do that either. It is just for demonstration.

Answer 2

Here is my work-around. It works like a charm for me. Hope it will help you.

1. Create a button and hide it by Css (NOT by code: button.setInvisible(false))

   final Button downloadInvisibleButton = new Button();
   downloadInvisibleButton.setId("DownloadButtonId");
   downloadInvisibleButton.addStyleName("InvisibleButton");
   

   In your theme, add this rule to hide the downloadInvisibleButton:

   .InvisibleButton {
       display: none;
   }
   

2. When the user clicks on menuItem: extend the fileDownloader to the downloadInvisibleButton, then simulate the click on the downloadInvisibleButton by JavaScript.

   menuBar.addItem("Download", new MenuBar.Command() {
     @Override
     public void menuSelected(MenuBar.MenuItem selectedItem) {
       FileDownloader fileDownloader = new FileDownloader(...);
       fileDownloader.extend(downloadInvisibleButton);
       //Simulate the click on downloadInvisibleButton by JavaScript
       Page.getCurrent().getJavaScript()
          .execute("document.getElementById('DownloadButtonId').click();");
     }
   });