C# 以编程方式更改应用程序语言-UWP

我已经为法语和英语创建了资源文件（

.resw

）。现在我想在加载我的应用程序的第一页时调用“fr”的资源文件。我做了如下的事情。但它显示了一个例外

“System.NullReferenceException:对象引用未设置为 对象的实例”

XAML

<TextBlock x:Uid="txt_launch3" Grid.Row="4"  Padding="7"/>

---

问题是您在页面中过早调用该方法。在构造函数中，页面尚未分配给它所在的

框架。因此，
帧
仍在那里

您可以将方法调用移动到
OnNavigatedTo
覆盖：

protected override void OnNavigatedTo(NavigationEventArgs e)
{
    base.OnNavigatedTo(e);
    string getDeviceDefaultLang = "fr";
    ChangeLanguage2(getDeviceDefaultLang);
}

private void ChangeLanguage2(string language)
{
    try
    {
        ApplicationLanguages.PrimaryLanguageOverride = language;
        Frame.CacheSize = 0;
        Windows.ApplicationModel.Resources.Core.ResourceContext.GetForCurrentView().Reset();
        Windows.ApplicationModel.Resources.Core.ResourceContext.GetForViewIndependentUse().Reset();
        Frame.Navigate(this.GetType());
    }
    catch (Exception ex)
    {
        string exx = ex.ToString(); //getting System.NullReferenceException            
    }
}

此外，您可以直接访问应用程序的根框架，而不是通过页面的
frame
属性：

private void ChangeLanguage2(string language)
{
    try
    {
        ApplicationLanguages.PrimaryLanguageOverride = language;
        var rootFrame = Window.Current.Content as Frame;
        rootFrame.CacheSize = 0;
        Windows.ApplicationModel.Resources.Core.ResourceContext.GetForCurrentView().Reset();
        Windows.ApplicationModel.Resources.Core.ResourceContext.GetForViewIndependentUse().Reset();
        rootFrame.Navigate(this.GetType());
    }
    catch (Exception ex)
    {
        string exx = ex.ToString(); //getting System.NullReferenceException            
    }
}

但是，这并不是最优的，因为您实际上是在导航，而当前正在进行导航（原始
MainPage
navigation）

您很可能会调用更改语言来响应用户操作（如单击按钮），而这一切都不再是问题，并且将定义
Frame

更新
最好的解决方案是在
App.xaml.cs
中的
OnLaunched
处理程序中设置语言覆盖：

protected override void OnLaunched(LaunchActivatedEventArgs e)
{
    Frame rootFrame = Window.Current.Content as Frame;

    // Do not repeat app initialization when the Window already has content,
    // just ensure that the window is active
    if (rootFrame == null)
    {
        // Create a Frame to act as the navigation context and navigate to the first page
        rootFrame = new Frame();

        rootFrame.NavigationFailed += OnNavigationFailed;

        if (e.PreviousExecutionState == ApplicationExecutionState.Terminated)
        {
            //TODO: Load state from previously suspended application
        }

        // Place the frame in the current Window
        Window.Current.Content = rootFrame;
    }

    if (e.PrelaunchActivated == false)
    {
        if (rootFrame.Content == null)
        {
            ApplicationLanguages.PrimaryLanguageOverride = "fr";
            Windows.ApplicationModel.Resources.Core.ResourceContext.GetForCurrentView().Reset();
            Windows.ApplicationModel.Resources.Core.ResourceContext.GetForViewIndependentUse().Reset();

            // When the navigation stack isn't restored navigate to the first page,
            // configuring the new page by passing required information as a navigation
            // parameter
            rootFrame.Navigate(typeof(MainPage), e.Arguments);
        }
        // Ensure the current window is active
        Window.Current.Activate();
    }
}

异常发生在哪一行？哪个对象为空？现在没有显示任何异常。但语言没有改变。是不是rootFrame.CacheSize=0；导致了问题？请您在单击按钮后尝试执行该方法，看看它是否有效？但我的目的不同。第一次启动应用程序时，我希望在系统中显示文本的默认语言。问题是，当您在构造函数中调用
导航
时，“newly”创建的页面将首先显示，然后它将被不包含更新语言的旧页面覆盖。您确实需要至少将代码移动到
on导航到
，或者在
App.xaml.cs
中从
OnLaunched
的末尾调用它。此外，如果您想以系统语言显示文本，您应该ldn无需执行任何操作，系统语言是默认语言，您可以使用
PrimaryLanguageOverride
来使用与系统默认语言不同的语言。我已经用一个示例更新了我的答案，说明了如何在第一次导航之前应用该语言，因此甚至不需要进行帧缓存编辑
protected override void OnLaunched(LaunchActivatedEventArgs e)
{
    Frame rootFrame = Window.Current.Content as Frame;

    // Do not repeat app initialization when the Window already has content,
    // just ensure that the window is active
    if (rootFrame == null)
    {
        // Create a Frame to act as the navigation context and navigate to the first page
        rootFrame = new Frame();

        rootFrame.NavigationFailed += OnNavigationFailed;

        if (e.PreviousExecutionState == ApplicationExecutionState.Terminated)
        {
            //TODO: Load state from previously suspended application
        }

        // Place the frame in the current Window
        Window.Current.Content = rootFrame;
    }

    if (e.PrelaunchActivated == false)
    {
        if (rootFrame.Content == null)
        {
            ApplicationLanguages.PrimaryLanguageOverride = "fr";
            Windows.ApplicationModel.Resources.Core.ResourceContext.GetForCurrentView().Reset();
            Windows.ApplicationModel.Resources.Core.ResourceContext.GetForViewIndependentUse().Reset();

            // When the navigation stack isn't restored navigate to the first page,
            // configuring the new page by passing required information as a navigation
            // parameter
            rootFrame.Navigate(typeof(MainPage), e.Arguments);
        }
        // Ensure the current window is active
        Window.Current.Activate();
    }
}