Null conditional operator in bindings #18270
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We only had tests for the error states, and that was named incorrectly.
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You can test this PR using the following package version. |
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There's a scenario that isn't handled properly currently: a type cast followed by a null conditional operator.
For example, {Binding ((SomeType)First)?.Second, TargetNullValue='null!'} won't display the TargetNullValue if First is null.
Edit: shouldn't be part of this PR, this is changing how the cast works, see comments below.
Apart from that and two very minor points, this looks good to me!
| @@ -46,6 +46,20 @@ public bool TakeIf(char c) | |||
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| public bool TakeIf(string s) | |||
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New public API, is that intended? (I don't think CharacterReader should have been exposed in the first place.)
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Gah, no that wasn't intended. I didn't expect that class to be public!
| @@ -99,5 +113,17 @@ public void Skip(int count) | |||
| throw new IndexOutOfRangeException(); | |||
| _s = _s.Slice(count); | |||
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| private static bool SpanEquals(ReadOnlySpan<char> left, ReadOnlySpan<char> right) | |||
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Can be replaced with the built-in ROS.SequenceEqual().
Some users might expect invalid cast exception here (and so, FallbackValue to be used instead). We don't have any ...but at the same time, "?" might be a good enough indicator in the binding syntax. |
I now realize that this isn't the current behavior of the binding cast at all: After this PR, the nuance becomes a bit more important. |
What does the pull request do?
As described in #17029 adds support for the null-conditional operator (
?.) to reflection and compiled bindings.What is the current behavior?
If a null is encountered while evaluating in a binding path, then a warning will be logged and the binding will result in an error state. If such a binding is used in a multi-binding then the multi-binding will not produce a value as it will consider its input to be in an error state.
What is the updated/expected behavior with this PR?
One can now use the
?.operator in a binding path to indicate "it is expected that this property may be null". If this is the case then the binding will producenullinstead of an error. An example:Indicates that it is expected that
Thirdmay be null.Note that this PR does not implement the related
?[]operator for array indexing.Fixed issues
Fixes #17029