我們在Jx.Cms開發筆記（三）-Views主題動態切換中說了如何切換主題。但是這裡有一個問題，就是主題切換時，會報錯
這是由於asp.net core在處理Views的資訊的時候是在建構函式中處理的，沒有任何方法可以重新整理這個處理結果。
這裡放最新版的DefaultViewCompiler程式碼，在Jx.Cms編寫的時候程式碼有少許區別，但是基本邏輯是一樣的。
public DefaultViewCompiler(
ApplicationPartManager applicationPartManager,
ILogger<DefaultViewCompiler> logger)
{
_applicationPartManager = applicationPartManager;
_logger = logger;
_normalizedPathCache = new ConcurrentDictionary<string, string>(StringComparer.Ordinal);
EnsureCompiledViews(logger);
}
[MemberNotNull(nameof(_compiledViews))]
private void EnsureCompiledViews(ILogger logger)
{
if (_compiledViews is not null)
{
return;
}
var viewsFeature = new ViewsFeature();
_applicationPartManager.PopulateFeature(viewsFeature);
// We need to validate that the all compiled views are unique by path (case-insensitive).
// We do this because there's no good way to canonicalize paths on windows, and it will create
// problems when deploying to linux. Rather than deal with these issues, we just don't support
// views that differ only by case.
var compiledViews = new Dictionary<string, Task<CompiledViewDescriptor>>(
viewsFeature.ViewDescriptors.Count,
StringComparer.OrdinalIgnoreCase);
foreach (var compiledView in viewsFeature.ViewDescriptors)
{
logger.ViewCompilerLocatedCompiledView(compiledView.RelativePath);
if (!compiledViews.ContainsKey(compiledView.RelativePath))
{
// View ordering has precedence semantics, a view with a higher precedence was not
// already added to the list.
compiledViews.TryAdd(compiledView.RelativePath, Task.FromResult(compiledView));
}
}
if (compiledViews.Count == 0)
{
logger.ViewCompilerNoCompiledViewsFound();
}
// Safe races should be ok. We would end up logging multiple times
// if this is invoked concurrently, but since this is primarily a dev-scenario, we don't think
// this will happen often. We could always re-consider the logging if we get feedback.
_compiledViews = compiledViews;
}所以程式只能獲取到第一次的_compiledViews，切換後的Views由於沒有放在_compiledViews中，所以無法被找到，就出現了第一圖的那種錯誤。
這裡的解決方法很簡單，我們只需要重寫一個自己的ViewCompiler就可以了，由於官方原始碼全部都是internal的，所以我們只能把這部分內容全部重寫。
我們建立自己的MyViewCompilerProvider和MyViewCompiler。由於.Net6在這裡有部分修改，我們的程式是在.Net5時編寫的，所以這裡我們的原始碼是.Net5修改的，與目前最新的程式碼有些許差距，但是不影響正常使用.
MyViewCompiler:
public class MyViewCompiler : IViewCompiler
{
private readonly Dictionary<string, Task<CompiledViewDescriptor>> _compiledViews;
private readonly ConcurrentDictionary<string, string> _normalizedPathCache;
private readonly ILogger _logger;
public MyViewCompiler(
IList<CompiledViewDescriptor> compiledViews,
ILogger logger)
{
if (compiledViews == null)
{
throw new ArgumentNullException(nameof(compiledViews));
}
if (logger == null)
{
throw new ArgumentNullException(nameof(logger));
}
_logger = logger;
_normalizedPathCache = new ConcurrentDictionary<string, string>(StringComparer.Ordinal);
// We need to validate that the all of the precompiled views are unique by path (case-insensitive).
// We do this because there's no good way to canonicalize paths on windows, and it will create
// problems when deploying to linux. Rather than deal with these issues, we just don't support
// views that differ only by case.
_compiledViews = new Dictionary<string, Task<CompiledViewDescriptor>>(
compiledViews.Count,
StringComparer.OrdinalIgnoreCase);
foreach (var compiledView in compiledViews)
{
if (!_compiledViews.ContainsKey(compiledView.RelativePath))
{
// View ordering has precedence semantics, a view with a higher precedence was not
// already added to the list.
_compiledViews.Add(compiledView.RelativePath, Task.FromResult(compiledView));
}
}
if (_compiledViews.Count == 0)
{
}
}
/// <inheritdoc />
public Task<CompiledViewDescriptor> CompileAsync(string relativePath)
{
if (relativePath == null)
{
throw new ArgumentNullException(nameof(relativePath));
}
// Attempt to lookup the cache entry using the passed in path. This will succeed if the path is already
// normalized and a cache entry exists.
if (_compiledViews.TryGetValue(relativePath, out var cachedResult))
{
return cachedResult;
}
var normalizedPath = GetNormalizedPath(relativePath);
if (_compiledViews.TryGetValue(normalizedPath, out cachedResult))
{
return cachedResult;
}
// Entry does not exist. Attempt to create one.
return Task.FromResult(new CompiledViewDescriptor
{
RelativePath = normalizedPath,
ExpirationTokens = Array.Empty<IChangeToken>(),
});
}
private string GetNormalizedPath(string relativePath)
{
Debug.Assert(relativePath != null);
if (relativePath.Length == 0)
{
return relativePath;
}
if (!_normalizedPathCache.TryGetValue(relativePath, out var normalizedPath))
{
normalizedPath = NormalizePath(relativePath);
_normalizedPathCache[relativePath] = normalizedPath;
}
return normalizedPath;
}
public static string NormalizePath(string path)
{
var addLeadingSlash = path[0] != '\\' && path[0] != '/';
var transformSlashes = path.IndexOf('\\') != -1;
if (!addLeadingSlash && !transformSlashes)
{
return path;
}
var length = path.Length;
if (addLeadingSlash)
{
length++;
}
return string.Create(length, (path, addLeadingSlash), (span, tuple) =>
{
var (pathValue, addLeadingSlashValue) = tuple;
var spanIndex = 0;
if (addLeadingSlashValue)
{
span[spanIndex++] = '/';
}
foreach (var ch in pathValue)
{
span[spanIndex++] = ch == '\\' ? '/' : ch;
}
});
}
}這個類完全複製了.Net5的原始碼，只是刪除了部分編譯不過去的日誌內容。
MyViewCompilerProvider：
public class MyViewCompilerProvider : IViewCompilerProvider
{
private MyViewCompiler _compiler;
private readonly ApplicationPartManager _applicationPartManager;
private readonly ILoggerFactory _loggerFactory;
public MyViewCompilerProvider(
ApplicationPartManager applicationPartManager,
ILoggerFactory loggerFactory)
{
_applicationPartManager = applicationPartManager;
_loggerFactory = loggerFactory;
Modify();
}
public void Modify()
{
var feature = new ViewsFeature();
_applicationPartManager.PopulateFeature(feature);
_compiler = new MyViewCompiler(feature.ViewDescriptors, _loggerFactory.CreateLogger<MyViewCompiler>());
}
public IViewCompiler GetCompiler() => _compiler;
}這個類我們只是把.Net5原始碼裡的建構函式拆分了，拆出了一個Public的Modify方法。
然後我們需要用自己的MyViewCompilerProvider替換自帶的，所以我們需要在Startup.cs的ConfigureServices方法中新增services.Replace<IViewCompilerProvider, MyViewCompilerProvider>();
最後我們只需要在需要重新獲取所有Views的地方呼叫viewCompilerProvider?.Modify();即可。