The way I ended up solving this was as follows. Remember I need to extract the localized texts from a database/remote api.
With this solution I can databind like this and all bound texts will change automatically when I change the language:
<Label Content="{Binding Path=Strings.ErrorLevelColumnHeaderLabel}"/>
Of course the Strings object must be accessible from all datacontexts.
The strings are stored in a database table that looks like this, an ID-column and one column for each of the supported languages:
ID en da de
24 'Level' 'Niveau' 'Stufe'
I created a UIStringsVM class which implements the INotifyPropertyChanged interface. In my example I have implemented this in a base class called Observable, which I am sure many others have as well. See this answer for details.
public class UIStringsVM : Observable
{
public static UIStringsVM CurrentStringsInstance;
private bool stringsAreLoading = false;
private Dictionary<int, string> stringDictionary;
}
The UIStringsVM class have a property for each string I need to have localized. Since the class supports the INotifyPropertyChanged interface through the base class I can then rely on changes to be reflected in the UI when ever the language changes.
Inside the UIStringsVM class the strings for the current language is stored in a Dictionary<int, string>. The reason for this is that I can use the string ID from the database to access the correct string.
Now I can use the ID inside the property Get method to return whatever string is stored for that value. So the properties will look like this:
public string ErrorLevelColumnHeaderLabel
{
get =>
this.stringDictionary[24].Replace("\\n", Environment.NewLine);
private set =>
this.stringDictionary[24] = value;
}
The properties are never set individually so the setter could be omitted.
The constructor:
public UIStringsVM()
{
this.stringDictionary = new Dictionary<int, string>();
// Initialize with default values. The ! at the end makes it easier to identify missing values in the database.
this.LoginButtonText = "Login!";
this.LogoutButtonText = "Logout!";
this.UserLabelFormatString = "{0} logged in!";
this.ErrorLevelColumnHeaderLabel = "Level!";
UIStringsVM.CurrentStringsInstance = this;
}
In order to load the strings I use the following method:
public async Task LoadStringsAsync(string languageCode, CancellationToken ct)
{
if (languageCode.Length != 2)
throw new ArgumentException("languageCode must be exactly 2 characters.", nameof(languageCode));
this.StringsAreLoading = true;
var client = new UIStringsClient(AppVM.BaseURL);
try
{
var apiStrings = await client.GetByLanguageAsync(languageCode, ct);
foreach (var r in apiStrings)
{
/* Note: this will make it impossible to overwrite a string with an empty string from the database,
* thus always keeping the string defined in this class' constructor. However strings will always
* have a value as defined in the constructor even if one does not exist in the database.
* */
if (string.IsNullOrWhiteSpace(r.Value))
continue;
this.stringDictionary[r.Key] = r.Value;
}
this.OnPropertyChanged((string)null); // Raise a change event for the entire object, not just a named property
}
finally
{
this.StringsAreLoading = false;
}
}
I hope this helps anyone who might happen to come across this late answer. I have been running this solution for 15 months or so, and its been really great to work with.
