Blazor 服务器存储初始查询参数

Question

Problem: Storing startup query strings for the life of the session. These startup query strings are optional parameters ("?mode=run") and do not persist between pages. I'm having a hard time finding a single entry point to set the ProtectedSessionStorage .

1. First I tried a scoped service with dependency injection. That works great until the user refreshes the page.

private RunModeSettings _rms = new RunModeSettings();
private readonly ProtectedSessionStorage _protectedSessionStore;
private readonly NavigationManager _navManager;
public RunModeService(ProtectedSessionStorage ProtectedSessionStore, NavigationManager NavManager)
{
    // Constructor is called again if user refreshes the page.
    // If the user is on a page that does not contain the startup query string
    // then the query string is lost / overwritten with null.
    _protectedSessionStore = ProtectedSessionStore;
    _navManager = NavManager;
    _navManager.TryGetQueryString("mode", out string mode);
    // ProtectedSessionStorage is async only
    // Can't check or set session storage
    _rms.RunMode = mode;
         
}

Since ProtectedSessionStorage is alive for the lifetime of the tab I thought I could check the session storage in the service constructor to handle the refresh. Unfortunately there is no synchronous version to use in the service constructor.

2. Secondly I tried to store the query string parameters by overriding OnInitializedAsync .

// App.razor
protected override async Task OnInitializedAsync()
{
    _navManager.TryGetQueryString("mode", out string mode);
    if ((await _protectedSessionStore.GetAsync<RunModeSettings>("RMS")).Value == null)
        await _protectedSessionStore.SetAsync("RMS", new RunModeSettings() { RunMode = mode});

}

Since we can only use ProtectedSessionStorage in asynchronous overrides it's not guaranteed that OnInitializedAsync in App.Razor component is completed before continuation. This introduces a race condition between other early components like <App> , <NavMenu> and <MainLayout> .

In asp.net I could use the Session_Start event as an entry point to store my startup query parameters for the rest of session. Is there a similar entry point in Bazor?

Answer 1

I came up with something not so elegant but it's simple and works good. I register the scoped service as usual.

builder.Services.AddScoped<RunModeService>();

The scoped services job is to maintain startup query string parameters inside an object named RunModeSettings . Upon construction of the service I use dependency injection to access the query string. I store the settings object in the session storage incase a refresh happens on a page that does not include the startup query string parameters.

To handle the race condition RunModeSettings are accessed via GetRunModeSettingsAsync . It returns the object that the service was constructed with or pulls it from the session if ready.

public class RunModeService
{
    private RunModeSettings _rms = new RunModeSettings();
    private readonly ProtectedSessionStorage _protectedSessionStore;
    private readonly NavigationManager _navManager;
    public RunModeService(ProtectedSessionStorage ProtectedSessionStore, NavigationManager NavManager)
    {
        _protectedSessionStore = ProtectedSessionStore;
        _navManager = NavManager;
        // Get optional parameters.
        _navManager.TryGetQueryString("mode",out string mode);
        _rms.RunMode = mode;
        // Fire and forget.
        SetRunModeAsync(); 
    }
    public async Task SetRunModeAsync()
    {
        if ((await _protectedSessionStore.GetAsync<RunModeSettings>("RMS")).Value == null)
            await _protectedSessionStore.SetAsync("RMS", _rms);
    }

    public async Task<RunModeSettings> GetRunModeSettingsAsync()
    {
        return (await _protectedSessionStore.GetAsync<RunModeSettings>("RMS")).Value ?? _rms;
    }

}

Now the lifetime of my settings within the service are not determined by the service scope. In my case I use ProtectedSessionStorage to keep the lifetime with the tab. Finally, we can access our service as usual.

@inject RunModeService _rms; // Page inject
[Inject] public RunModeService rms { get; set; } // Or code inject

var rms = await _rms.GetRunModeSettingsAsync();