// It's internal because there isn't a known use case for user code comparing
// ParameterCollection instances, and even if there was, it's unlikely it should
// use these equality rules which are designed for their effect on rendering.
internal bool DefinitelyEquals(ParameterCollection oldParameters)
{
// In general we can't detect mutations on arbitrary objects. We can't trust
// things like .Equals or .GetHashCode because they usually only tell us about
// shallow changes, not deep mutations. So we return false if both:
// [1] All the parameters are known to be immutable (i.e., Type.IsPrimitive
// or is in a known set of common immutable types)
// [2] And all the parameter values are equal to their previous values
// Otherwise be conservative and return false.
// To make this check cheaper, since parameters are virtually always generated in
// a deterministic order, we don't bother to account for reordering, so if any
// of the names don't match sequentially we just return false too.
//
// The logic here may look kind of epic, and would certainly be simpler if we
// used ParameterEnumerator.GetEnumerator(), but it's perf-critical and this
// implementation requires a lot fewer instructions than a GetEnumerator-based one.
var oldIndex = oldParameters._ownerIndex;
var newIndex = _ownerIndex;
var oldEndIndexExcl = oldIndex + oldParameters._frames[oldIndex].ComponentSubtreeLength;
var newEndIndexExcl = newIndex + _frames[newIndex].ComponentSubtreeLength;
while (true)
{
// First, stop if we've reached the end of either subtree
oldIndex++;
newIndex++;
var oldFinished = oldIndex == oldEndIndexExcl;
var newFinished = newIndex == newEndIndexExcl;
if (oldFinished || newFinished)
{
return(oldFinished == newFinished); // Same only if we have same number of parameters
}
else
{
// Since neither subtree has finished, it's safe to read the next frame from both
ref var oldFrame = ref oldParameters._frames[oldIndex];
ref var newFrame = ref _frames[newIndex];
// Stop if we've reached the end of either subtree's sequence of attributes
oldFinished = oldFrame.FrameType != RenderTreeFrameType.Attribute;
newFinished = newFrame.FrameType != RenderTreeFrameType.Attribute;
if (oldFinished || newFinished)
{
return(oldFinished == newFinished); // Same only if we have same number of parameters
}
else
{
if (!string.Equals(oldFrame.AttributeName, newFrame.AttributeName, StringComparison.Ordinal))
{
return(false); // Different names
}
var oldValue = oldFrame.AttributeValue;
var newValue = newFrame.AttributeValue;
if (ChangeDetection.MayHaveChanged(oldValue, newValue))
{
return(false);
}
}
}
/// <inheritdoc />
public void SetParameters(ParameterCollection parameters)
{
// Implementing the parameter binding manually, instead of just calling
// parameters.AssignToProperties(this), is just a very slight perf optimization
// and makes it simpler impose rules about the params being required or not.
var hasSuppliedValue = false;
var previousValue = Value;
var previousFixed = IsFixed;
Value = default;
ChildContent = null;
Name = null;
IsFixed = false;
foreach (var parameter in parameters)
{
if (parameter.Name.Equals(nameof(Value), StringComparison.OrdinalIgnoreCase))
{
Value = (T)parameter.Value;
hasSuppliedValue = true;
}
else if (parameter.Name.Equals(nameof(ChildContent), StringComparison.OrdinalIgnoreCase))
{
ChildContent = (RenderFragment)parameter.Value;
}
else if (parameter.Name.Equals(nameof(Name), StringComparison.OrdinalIgnoreCase))
{
Name = (string)parameter.Value;
if (string.IsNullOrEmpty(Name))
{
throw new ArgumentException($"The parameter '{nameof(Name)}' for component '{nameof(CascadingValue<T>)}' does not allow null or empty values.");
}
}
else if (parameter.Name.Equals(nameof(IsFixed), StringComparison.OrdinalIgnoreCase))
{
IsFixed = (bool)parameter.Value;
}
else
{
throw new ArgumentException($"The component '{nameof(CascadingValue<T>)}' does not accept a parameter with the name '{parameter.Name}'.");
}
}
if (_hasSetParametersPreviously && IsFixed != previousFixed)
{
throw new InvalidOperationException($"The value of {nameof(IsFixed)} cannot be changed dynamically.");
}
_hasSetParametersPreviously = true;
// It's OK for the value to be null, but some "Value" param must be suppled
// because it serves no useful purpose to have a <CascadingValue> otherwise.
if (!hasSuppliedValue)
{
throw new ArgumentException($"Missing required parameter '{nameof(Value)}' for component '{nameof(Parameter)}'.");
}
// Rendering is most efficient when things are queued from rootmost to leafmost.
// Given a components A (parent) -> B (child), you want them to be queued in order
// [A, B] because if you had [B, A], then the render for A might change B's params
// making it render again, so you'd render [B, A, B], which is wasteful.
// At some point we might consider making the render queue actually enforce this
// ordering during insertion.
//
// For the CascadingValue component, this observation is why it's important to render
// ourself before notifying subscribers (which can be grandchildren or deeper).
// If we rerendered subscribers first, then our own subsequent render might cause an
// further update that makes those nested subscribers get rendered twice.
_renderHandle.Render(Render);
if (_subscribers != null && ChangeDetection.MayHaveChanged(previousValue, Value))
{
NotifySubscribers();
}
}