129 lines
6.6 KiB
Markdown
129 lines
6.6 KiB
Markdown
# Dynamic queries flag migration
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# 动态查询标志的迁移
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## What does this migration do?
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## 这种迁移是做什么的？
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In Angular version 8, a schematic added `static` flags to all `@ViewChild()` and `@ContentChild()` queries.
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This was the first step towards changing the default behavior.
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With version 9, the default value changes to `static: false` and the flag becomes optional.
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在 Angular 的 8 版本中，升级原理图为所有 `@ViewChild()` 和 `@ContentChild()` 查询都添加了 `static` 标志。这是改变默认行为的第一步。在版本 9 中，默认值变成了 `static: false`，该标志变为可选的。
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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`.
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If so, the schematic removes the flag, as it now matches the default.
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该原理图扫描了编译中的类，并为每个类检查这些成员是否有 `static` 标志设置为 `false` 的 `@ViewChild()` 或 `@ContentChild()` 查询。如果是这样，该原理图会移除该标志，因为它现在是默认值了。
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**Before:**
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**之前：**
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```ts
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@ViewChild('foo', {static: false}) foo: ElementRef;
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@ViewChild('bar', {static: true}) bar: ElementRef;
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```
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**After:**
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**之后：**
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```ts
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@ViewChild('foo') foo: ElementRef;
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// this query doesn't change because the static value is true
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@ViewChild('bar', {static: true}) bar: ElementRef;
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```
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Note that the flag is not supported in `@ViewChildren()` or `@ContentChildren()` queries, so the schematic will not check these properties.
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请注意，`@ViewChildren()` 或 `@ContentChildren()` 查询中不支持该标志，因此该原理图不会检查这些属性。
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## Why is this migration necessary?
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## 为何这次迁移必不可少？
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This schematic performs a code cleanup to remove `static` flags that match the default, as they are no longer necessary.
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Functionally, the code change should be a noop.
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这个原理图执行代码清理工作来移除与默认值相匹配的 `static` 标志，因为它们不再是必需的。从功能上讲，这种代码更改应该没有影响。
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Before version 9, Angular figured out the static or dynamic nature of a query automatically, based on how the template was written.
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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)).
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As of version 9, Angular uses dynamic queries (`static: false`) by default, which simplifies queries.
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Developers can still explicitly set a query to `static: true` if necessary.
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在版本 9 之前，Angular 会根据模板的编写方式来自动判定查询应该是静态的还是动态的。然而，以这种方式处理模板会导致错误和意外行为（请参阅[静态查询迁移指南](guide/static-query-migration#what-does-this-flag-mean)中的更多内容）。所以，从版本 9 开始，Angular 默认使用动态查询（ `static: false` ），简化了查询过程。开发人员仍然可以把查询显式设置为 `static: true`。
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<div class=" alert is-helpful">
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### What is the difference between static and dynamic queries?
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### 静态查询和动态查询有什么区别？
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The `static` option for `@ViewChild()` and `@ContentChild()` queries determines when the query results become available.
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`@ViewChild()` 和 `@ContentChild()` 查询的 `static` 选项决定了其查询结果何时可用。
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With static queries (`static: true`), the query resolves once the view has been created, but before change detection runs.
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The result, though, will never be updated to reflect changes to your view, such as changes to `ngIf` and `ngFor` blocks.
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使用静态查询（ `static: true` ）时，视图刚刚被创建，还没有运行变更检测之前，此查询就会解析。但是，其结果永远不会更新，以反映对视图的更改，例如对 `ngIf` 和 `ngFor` 块的更改。
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With dynamic queries (`static: false`), the query resolves after either `ngAfterViewInit()` or `ngAfterContentInit()` for `@ViewChild()` and `@ContentChild()` respectively.
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The result will be updated for changes to your view, such as changes to `ngIf` and `ngFor` blocks.
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而使用动态查询（ `static: false` ）时，此查询会分别在 `ngAfterViewInit()` 或 `ngAfterContentInit()` 之后进行解析。此结果将随着对视图的更改而更新，例如对 `ngIf` 和 `ngFor` 块的更改。
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For more information, see the following entries in the
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[Static Query Migration Guide](guide/static-query-migration):
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要了解更多信息，请参见[静态查询迁移指南](guide/static-query-migration)中的以下条目：
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* [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)
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[如何选择使用哪个 `static` 标志值： `true` 还是 `false` ？](guide/static-query-migration#how-do-i-choose-which-static-flag-value-to-use-true-or-false)
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* [Is there a case where I should use `{static: true}`?](guide/static-query-migration#is-there-a-case-where-i-should-use-static-true)
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[哪些情况下我应该使用 `{static: true}` ？](guide/static-query-migration#is-there-a-case-where-i-should-use-static-true)
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</div>
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## What does this mean for libraries?
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## 这对库来说意味着什么？
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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.
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为了支持那些仍在运行版本 8 的应用，库中最安全的选项是保留 `static` 标志，以保持解析时序的一致性。
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- *Libraries on version 9 with applications running version 8: *
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*库的版本为 9，应用的版本为 8：*
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The schematic won't run on libraries.
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As long as libraries retain their `static` flags from version 8, they should work with apps on 8.
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该原理图不会在库中运行。只要库从版本 8 开始就保留了 `static` 标志，就同样可以在 8 上运行。
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- *Libraries on version 8 with applications running version 9: *
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*应用的版本为 9，库的版本为 8：*
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Libraries will have explicit flags defined.
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The behavior with explicit flags has not changed.
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库中中会定义显式的标志。只要带有显式标志，其行为就不会改变。
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### What about applications using non-migrated libraries?
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### 那些使用未迁移库的应用呢？
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Because this is a code cleanup that is a noop, non-migrated libraries will work the same either way.
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因为这只是一个什么也不做的代码清理工作，所以未迁移的库也同样可以工作。
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