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LaunchURL.md

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Opening a URL in a new tab/window

Launch URL allows opening a new browser tab (or window), by delegating the actual work to Power BI.

See commit for what was added at this step.

Note: custom visuals are hosted in Power BI inside sandboxed iframes, this prevents opening a new browser tab (or window) in "the usual way", e.g. using window.open('http://some.link.net','_blank').

Usage

Use the host.launchUrl() API call, passing your destenation URL as a string argument:

this.host.launchUrl('http://some.link.net');

Restrictions

  • Use only absolute paths, not relative ones. http://some.link.net/subfolder/page.html is fine, /page.html won't be opened.
  • Currently only http and https protocols are supported. Avoid ftp, mailto etc.

Best practices

  1. For most cases, it is best to only open a link as a response to a user's explicit action. Make it easy for the user to understand that clicking the link or button will result in opening a new tab. Triggering a launchUrl() call without a user's action, or as a side effect of a different action can be confusing or frustrating for the user.
  2. If the link is not crucial for the proper functioning of the visual, it is recommanded to provide the report's author a way to disable and hide the link. This is especially relevant for special Power BI use-cases, such as embedding a report in a 3rd party application or publishing it to the web.
  3. Avoid Triggering a launchUrl() call from inside a loop, the visual's update function, or any other frequently recurring code.

Step by step example

Adding a link launching element

The following lines were added to the visual's constructor function:

    this.helpLinkElement = this.createHelpLinkElement();
    options.element.appendChild(this.helpLinkElement);

And, a private function creating and attaching the anchor element was added:

private createHelpLinkElement(): Element {
    let linkElement = document.createElement("a");
    linkElement.textContent = "?";
    linkElement.setAttribute("title", "Open documentation");
    linkElement.setAttribute("class", "helpLink");
    linkElement.addEventListener("click", () => {
        this.host.launchUrl("https://github.com/Microsoft/PowerBI-visuals/blob/master/Readme.md#developing-your-first-powerbi-visual");
    });
    return linkElement;
};

Finally, an entry in the visual.less file defines the style for the link element (see here)

Adding a toggling mechanism

This requires adding a static object (see static object tutorial), so that the report's author can toggle the visibility of the link element (default is set to hidden). A showHelpLink boolean static object was added to capabilities.json objects entry:

"objects": {
//...
    "generalView": {
            "displayName": "General View",
            "properties": 
                //...
                "showHelpLink": {
                    "displayName": "Show Help Button",
                    "type": { 
                        "bool": true 
                    }
                }
            }
        }
    }

And, in the visual's update function, the following lines were added:

    if (settings.generalView.showHelpLink) {
        this.helpLinkElement.classList.remove("hidden");
    } else {
        this.helpLinkElement.classList.add("hidden");
    }

The hidden class is defined in visual.less to control the display of the element.