🧩 Why isn’t resolveWebviewView ever called in my VS Code extension?

I want to share a subtle but critical pitfall that can break VS Code sidebar webviews and waste hours of debugging time. If your resolveWebviewView() method never gets called—no errors, no logs, just a stubborn placeholder in the sidebar—this might be your culprit.

Symptoms

• You register your WebviewViewProvider in activate()

• Your extension activates as expected

• The sidebar icon and view show up in VS Code

• But resolveWebviewView() is never fired. There are no log messages and nothing appears in the sidebar but a placeholder and the error:
  "There is no data provider registered that can provide view data."

What’s Actually Happening

Despite what most documentation suggests, just defining a view with an id in your package.json and registering a provider with the matching ID is not enough.

VS Code will happily display your sidebar view, but will never hook up your provider unless you explicitly set the view’s type to "webview" in package.json.

The Critical Line

You need this in your package.json view contribution:

"views": {
  "mySidebarContainer": [
    {
      "type": "webview",  // <-- This is required!
      "id": "mySidebarView",
      "name": "Dashboard"
    }
  ]
}

If you leave off "type": "webview", VS Code treats your view as a static placeholder.
Your provider will never be called—no matter how perfect your code is.

Why is this so tricky?

• Your extension activates and compiles without any errors or warnings

• The sidebar icon and panel appear, giving the illusion that everything is wired up

• There is zero feedback from VS Code that the view provider isn’t actually being used

This makes it really hard to diagnose, especially in projects with build steps or lots of code.

Minimal Working Example

package.json (relevant bits):

"viewsContainers": {
  "activitybar": [
    {
      "id": "mySidebarContainer",
      "title": "My Sidebar",
      "icon": "media/icon.svg"
    }
  ]
},
"views": {
  "mySidebarContainer": [
    {
      "type": "webview",
      "id": "mySidebarView",
      "name": "Sidebar Webview"
    }
  ]
}

Activation:

vscode.window.registerWebviewViewProvider(
  "mySidebarView",
  new MySidebarViewProvider(context)
);

Provider:

export class MySidebarViewProvider implements vscode.WebviewViewProvider {
  resolveWebviewView(view: vscode.WebviewView) {
    view.webview.options = { enableScripts: true };
    view.webview.html = '<h1>It works!</h1>';
  }
}

Takeaway

If your sidebar webview isn’t working and resolveWebviewView is never called, double check that you included "type": "webview" in your view’s package.json entry.
This tiny detail makes all the difference and is easy to overlook.