8f1d0c317e
PR #36601 itroduces icons on all links if the link contains https:// or http:// but there were some internal links left which contained https://angular.io. Removed https://angular.io from all these links. PR Close #37157
83 lines
3.6 KiB
Markdown
83 lines
3.6 KiB
Markdown
|
|
# Dynamic queries flag migration
|
|
|
|
## What does this migration do?
|
|
|
|
In Angular version 8, a schematic added `static` flags to all `@ViewChild()` and `@ContentChild()` queries.
|
|
This was the first step towards changing the default behavior.
|
|
With version 9, the default value changes to `static: false` and the flag becomes optional.
|
|
|
|
This schematic scans classes in the compilation and for each class, checks if the members have a `@ViewChild()` or `@ContentChild()` query with the `static` flag set to `false`.
|
|
If so, the schematic removes the flag, as it now matches the default.
|
|
|
|
**Before:**
|
|
```ts
|
|
@ViewChild('foo', {static: false}) foo: ElementRef;
|
|
|
|
@ViewChild('bar', {static: true}) bar: ElementRef;
|
|
```
|
|
|
|
|
|
**After:**
|
|
```ts
|
|
@ViewChild('foo') foo: ElementRef;
|
|
|
|
// this query doesn't change because the static value is true
|
|
@ViewChild('bar', {static: true}) bar: ElementRef;
|
|
```
|
|
|
|
Note that the flag is not supported in `@ViewChildren()` or `@ContentChildren()` queries, so the schematic will not check these properties.
|
|
|
|
|
|
## Why is this migration necessary?
|
|
|
|
This schematic performs a code cleanup to remove `static` flags that match the default, as they are no longer necessary.
|
|
Functionally, the code change should be a noop.
|
|
|
|
Before version 9, Angular figured out the static or dynamic nature of a query automatically, based on how the template was written.
|
|
Looking at templates in this way, however, caused buggy and surprising behavior (see more about that in the [Static Query Migration Guide](guide/static-query-migration#what-does-this-flag-mean)).
|
|
As of version 9, Angular uses dynamic queries (`static: false`) by default, which simplifies queries.
|
|
Developers can still explicitly set a query to `static: true` if necessary.
|
|
|
|
|
|
<div class=" alert is-helpful">
|
|
|
|
### What is the difference between static and dynamic queries?
|
|
|
|
The `static` option for `@ViewChild()` and `@ContentChild()` queries determines when the query results become available.
|
|
|
|
With static queries (`static: true`), the query resolves once the view has been created, but before change detection runs.
|
|
The result, though, will never be updated to reflect changes to your view, such as changes to `ngIf` and `ngFor` blocks.
|
|
|
|
With dynamic queries (`static: false`), the query resolves after either `ngAfterViewInit()` or `ngAfterContentInit()` for `@ViewChild()` and `@ContentChild()` respectively.
|
|
The result will be updated for changes to your view, such as changes to `ngIf` and `ngFor` blocks.
|
|
|
|
For more information, see the following entries in the
|
|
[Static Query Migration Guide](guide/static-query-migration):
|
|
|
|
* [How do I choose which `static` flag value to use: `true` or `false`?](guide/static-query-migration#how-do-i-choose-which-static-flag-value-to-use-true-or-false)
|
|
|
|
* [Is there a case where I should use `{static: true}`?](guide/static-query-migration#is-there-a-case-where-i-should-use-static-true)
|
|
|
|
</div>
|
|
|
|
|
|
## What does this mean for libraries?
|
|
|
|
In order to support applications that are still running with version 8, the safest option for libraries is to retain the `static` flag to keep the resolution timing consistent.
|
|
|
|
- *Libraries on version 9 with applications running version 8: *
|
|
|
|
The schematic won't run on libraries.
|
|
As long as libraries retain their `static` flags from version 8, they should work with apps on 8.
|
|
|
|
- *Libraries on version 8 with applications running version 9: *
|
|
|
|
Libraries will have explicit flags defined.
|
|
The behavior with explicit flags has not changed.
|
|
|
|
|
|
### What about applications using non-migrated libraries?
|
|
|
|
Because this is a code cleanup that is a noop, non-migrated libraries will work the same either way.
|