CoreWebView2 is null

I got CoreWebView2 null

I use this two methods in c#

public void InvokeBrowserScript(string functionName, string parameter, Action action = null)
{
try
{
Log.Write($"Invoking script: {functionName}, parameter: {parameter}");
_webView.Dispatcher.InvokeAsync(async () =>
{
var message = new { messageType = functionName, messageData = parameter };
var json = JsonConvert.SerializeObject(message);
PostMessageToWeb(json);
action?.Invoke(json);

            });
        }
        catch (Exception ex)
        {
            Log.Write($"Invoking script error: {ex}");
        }
    }

    /// <summary>
    /// From the container code(C#) you can call PostWebMessageAsJson() to pass
    /// JSON object to Angular layer. We are passing the functionname(messageType) and data(messageData)
    /// In the angular layer we can access the functionname and data through window.chrome.webview.addEventListener  
    /// </summary>
    /// <param name="json"></param>
    private void PostMessageToWeb(string json)
    {
        _webView.CoreWebView2?.PostWebMessageAsJson(json);
    }

I used
///

/// Call the container code from web side (angular code)
/// In the angular code we can access container methods like - window.chrome.webview.hostObjects.external.MethodName()
///

private void AddHostObject()
{
_webView.CoreWebView2.AddHostObjectToScript("external", new WebViewModel());

    }

so when i call a c# method from angular window.chrome.webview?.hostObjects.external.GetDeviceStatus()

Below is the c# method

public void GetDeviceStatus()
{
Task.Run(() =>
{
Log.Write("GetDeviceStatusinvoked");
InvokeBrowserScript("getInDeviceStatusComplete", ThreadManager.GetInBayStatus());
});
}
By AddHostObject() it calls GetDeviceStatus() from angular 15 layer to container,
But when InvokeBrowserScript("getInDeviceStatusComplete", ThreadManager.GetDeviceStatus());
called then in CoreWebView2 is null (InvokeBrowserScript calls PostMessageToWeb(json); in which CoreWebview2 is null )
How to fix this?