为什么单击按钮时活动指示器需要将近 3 秒才能启动

Question

我在单独的 xaml 文件中有 ActivityIndicator。我在 MainPage xaml 中将其用作 CustomLoader。此 CustomLoader 可见性由 bool 变量 VisibleLoader 控制

<custom:CustomLoader IsVisible="{Binding VisibleLoader}" 
           AbsoluteLayout.LayoutBounds="0.5,0.5,1,1" 
           AbsoluteLayout.LayoutFlags="All" Grid.Row="2">
</custom:CustomLoader>

在MainPageViewModel 中，当我单击说明ActivityIndicator 的按钮时，开始需要一些时间。见下方代码

MainPageViewModel代码

private bool _visibleLoader = false;
public MainPageViewModel()
{
    VisibleLoader = true;
    current = this;
    GetAllProducts();
    SyncCommand = new Command(SyncDevice);
}

public bool VisibleLoader
{
    get
    {
        return _visibleLoader;
    }
    set
    {
        this._visibleLoader = value;
        NotifyPropertyChanged("VisibleLoader");
    }
}

按钮点击事件代码

public async void SyncDevice()
{
    try
    {
        VisibleLoader = true;
        IsBusy = true;
        PageMessage = string.Empty;
        var strSerialNumber = DependencyService.Get<IDataHelper>().GetIdentifier();
        //VisibleButtons = true;
        resourceService = new ResourceService(new RequestProvider());
        if (GlobalSettings.deviceId == 0)
        {
            DeviceDetails deviceDtls = await resourceService.GetDeviceDetails(strSerialNumber);
            GlobalSettings.deviceId = deviceDtls.Id.Value;
        }
        if (GlobalSettings.deviceId.ToString() != null)
        {
            DevicesList data = await resourceService.GetProducts(GlobalSettings.deviceId);
            //this.lstProducts = data.Devices[0].Products;
            this.lstProducts = data != null ? data.Devices[0].Products : null;
            if (lstProducts != null && lstProducts.Count != 0)
            {
                //Filter Products from Parameter file
                var filterProducts = GlobalSettings.GetFilterProducts();
                if (filterProducts.Count > 0)
                {
                    //lstProducts = lstProducts.Where(product => !filterProducts.Any(fp => product.Name.ToLowerInvariant().Contains(fp.ToLowerInvariant()))).ToList();
                    lstProducts = lstProducts.Where(product => filterProducts.Any(fp => product.Name.ToLowerInvariant().Contains(fp.ToLowerInvariant()))).ToList();
                }
                TotalProducts = lstProducts.Count;
                lstProducts = lstProducts.OrderBy(s => s.Order).ThenBy(s => s.Name).ToList();
            }
            else
            {
                PageMessage = "No products found.";
            }
        }
        else
        {
            PageMessage = "Error occured. Please try again later.!";
        }
        NotifyPropertyChanged("lstProducts");
        resourceService = new ResourceService(new RequestProvider());
        await resourceService.SyncDevice(GlobalSettings.deviceId);
    }
    catch (Exception)
    {
        VisibleLoader = false;
    }
    VisibleLoader = false;
    IsBusy = false;
}
}

xaml 文件中的按钮

 <Button Text="Sync device" Command="{Binding SyncCommand}" HorizontalOptions="FillAndExpand"
                    BackgroundColor="LightBlue"  Margin="5" TextColor="White" BorderRadius="10" HeightRequest="40"></Button>

我该如何解决这个问题？

Answer 1

首先，如果您的同步设备方法不是一个事件，我建议您将其作为一个任务，因为异步无效不是一个好习惯。

public async Task SyncDevice()

另外，可能是你的布尔值在主线程中没有改变，这反过来又导致了这种情况，所以尝试类似

Device.BeginInvokeOnMainThread(()=>{ //Change visibility... });

确保只在此处添加相关代码，因为这会阻塞主线程，进而导致 UI 冻结

更新

那么你的命令看起来像：

new Command(async ()=>{await SyncDevice()});