Question

每次单击按钮时，以下代码都会触发。它有效，但我意识到每次播放声音时都不应检查声音状态和音量。但是，我似乎无法弄清楚如何让ViewModel以任何其他方式更新ApplicationData。我有一个设置ViewModel，它使用toggleswitch和音量滑块设置声音状态。

理想情况下，我认为，ViewModel会在导航回来时更新类变量，或者设置ViewModel会在此ViewModel中调用更新方法。但我似乎无法让它工作，除了在PlaySound方法中更新它。

  update
Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:346:11)
    at ServerResponse.header (/home/saunish/WebstormProjects/priceDrop/node_modules/express/lib/response.js:718:10)
    at ServerResponse.send (/home/saunish/WebstormProjects/priceDrop/node_modules/express/lib/response.js:163:12)
    at done (/home/saunish/WebstormProjects/priceDrop/node_modules/express/lib/response.js:957:10)
    at View.exports.renderFile [as engine] (/home/saunish/WebstormProjects/priceDrop/node_modules/ejs/lib/ejs.js:355:10)
    at View.render (/home/saunish/WebstormProjects/priceDrop/node_modules/express/lib/view.js:126:8)
    at tryRender (/home/saunish/WebstormProjects/priceDrop/node_modules/express/lib/application.js:639:10)
    at EventEmitter.render (/home/saunish/WebstormProjects/priceDrop/node_modules/express/lib/application.js:591:3)
    at ServerResponse.render (/home/saunish/WebstormProjects/priceDrop/node_modules/express/lib/response.js:961:7)
    at /home/saunish/WebstormProjects/priceDrop/app.js:130:13
Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:346:11)
    at ServerResponse.header (/home/saunish/WebstormProjects/priceDrop/node_modules/express/lib/response.js:718:10)
    at ServerResponse.send (/home/saunish/WebstormProjects/priceDrop/node_modules/express/lib/response.js:163:12)
    at done (/home/saunish/WebstormProjects/priceDrop/node_modules/express/lib/response.js:957:10)
    at View.exports.renderFile [as engine] (/home/saunish/WebstormProjects/priceDrop/node_modules/ejs/lib/ejs.js:355:10)
    at View.render (/home/saunish/WebstormProjects/priceDrop/node_modules/express/lib/view.js:126:8)
    at tryRender (/home/saunish/WebstormProjects/priceDrop/node_modules/express/lib/application.js:639:10)
    at EventEmitter.render (/home/saunish/WebstormProjects/priceDrop/node_modules/express/lib/application.js:591:3)
    at ServerResponse.render (/home/saunish/WebstormProjects/priceDrop/node_modules/express/lib/response.js:961:7)
    at /home/saunish/WebstormProjects/priceDrop/app.js:168:13

Answer 1

每当我需要在多个视图模型之间共享行为时（这里，您的行为是“存储和检索设置”），我实现了一个“服务”。在您的情况下，它可能看起来像：

public class SettingsService
{
    private readonly ApplicationDataContainer localSettings = ApplicationData.Current.LocalSettings;

    private double? localSoundVolume;

    public double LocalSoundVolume
    {
        get
        {
            if (this.localSoundVolume == null)
            {
                this.localSoundVolume = Convert.ToDouble(localSettings.Values["localSoundVolumeSetting"])
            }

            return this.localSoundVolume;
        }

        set
        {
            this.localSoundVolume = value;
            localSettings.Values["localSoundVolumeSetting"] = value;
        }       
    }
}

然后，您只需将服务注册为单例并在视图模型中检索它。理想情况下，您可以通过使用依赖注入来实现，但如果您使用的任何MVVM框架都没有提供IoC机制，那么服务定位器可以完成这项工作。从那里开始，只需从SettingsViewModel设置SettingsService.LocalSoundVolume属性并从其他视图模型中读取它即可。由于该值已缓存，因此您只需从ApplicationData设置中检索一次。

遵循此模式，您应该能够从视图模型中删除对ApplicationData的所有引用。

ApplicationData设置更改后如何更新ViewModel类变量？

1 个答案: