angular / angular/components

bug(MatTabLink): Underline (MatTabInk) is missing if combined with route reuse strategy

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area: material/tabs P3
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TypeScript
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描述

### Is this a regression?

- [ ] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

_No response_

### Description

We have an application with multiple layer of tabs combined with custom route reuse strategy. Most of the tabs are detached and reattached until the tab is closed.

The active tab is determined from the currently active route on each navigation end event. This way if the application is loaded with a specific url, the appropriate tab is selected.

Consider the following routes:
```
- /tab1
- /tab2
- /tab2/sub1
- /tab2/sub2
```

On the `/tab2` route, another tab group is present with links to the sub routes (and of course a sub router-outlet as well).

If we load the app with the `/tabs2/sub2` route, the components of `/tab2` and `/tab2/sub2` are loaded, which also means that the tab2's ink is initialized to the second tab in the header.

Now, if we navigate to `/tab1`, these components are not destroyed, however the tab link active flags are set to false because neither `/tab2/sub1` nor `/tab2/sub2` is active after the navigation ends.

Then if we navigate back to `/tab2/sub2`, the components are not reinitialized (because of the reuse strategy). but the active flag is changed for the `/tab2/sub2` tab link (because it is now active after navigation end).

### Reproduction

StackBlitz link: https://stackblitz.com/edit/stackblitz-starters-nckgfk?file=src%2Ftab-active-tracker.directive.ts

Steps to reproduce:
1. Click on Tab 1 -> Tab 1 highlighted [OK]
2. Click on Tab 2 -> Tab 2 highlighted [OK], inner tab group loaded [OK]
3. Click on Sub-Tab 1 -> upper Sub-Tab 1 highlighted [OK], inner Sub-Tab 1 highlighted [OK]
4. Click on Sub-Tab 2 -> upper Sub-Tab 2 highlighted [OK], inner Sub-Tab 2 highlighted [OK]
5. Click on Tab 1 -> Tab 1 highlighted [OK]
6. Click on Sub-Tab 2 -> Tab 2 highlighted [OK], **inner Sub 2 is NOT highlighted [NOK]**

### Expected Behavior

After the step 6 the ink should be re-initialized even if set to the same value.

### Actual Behavior

As you can see, the active status is properly set (font is bold on the inner Sub-Tab 2 header element) but the ink is missing.

However, I think I found the root cause of the problem.

When we navigate from the `/tab2/sub2` back to `/tab1`, neither the `/tab2/sub1` nor the `/tab2/sub2` routes are active so the `selectedIndex` is set to `-1` and the ink's `hide()` is called. However, the index just set is not processed until the next `ngAfterContentChecked` call.

Now, when we navigate back to `/tab2/sub2` (which was the last active inner tab) the ink handler thinks that despite the selection index is changed (from `-1` ro `1`), the selection itself is not changed.

I think that in the `hide()` function of `MatInkBar` the `this._currentItem` should be set to `null`. Because next time when `alignToElement` is called, the `correspondingItem === currentItem` check will be true (but the index was changed from `1 -> -1 -> 1` but it was not processed due to a missing `ngAfterContentChecked` call)

https://github.com/angular/components/blob/0762d69b394343555488b5aaada9444dd1a5083a/src/material/tabs/ink-bar.ts#L40

### Environment

```
Angular CLI: 17.0.5
Node: 18.18.0
Package Manager: npm 9.8.1
OS: win32 x64

Angular: 17.0.5
... animations, cli, common, compiler, compiler-cli, core, forms
... platform-browser, platform-browser-dynamic, router

Package Version
---------------------------------------------------------
@angular-devkit/architect 0.1700.5
@angular-devkit/build-angular 17.0.5
@angular-devkit/core 17.0.5
@angular-devkit/schematics 17.0.5
@angular/cdk 17.0.2
@angular/material 17.0.2
@schematics/angular 17.0.5
rxjs 7.8.1
typescript 5.2.2
zone.js 0.14.2
```

贡献指南

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调研方向

从 src/material/tabs/ink-bar.ts 开始,重点查看 MatInkBar.hide() 和 alignToElement(),然后在链接的 StackBlitz 中重现 route-reuse 序列。检查从 /tab2/sub2 转到 /tab1 再返回的过程;返回后内层 Sub-Tab 2 的 ink 再次可见即表示完成。

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评估

技术栈
angular, typescript
领域
frontend
Issue 类型
缺陷
难度
3/5
预计耗时
1-2 天
活跃度
停滞
描述清晰度
描述清楚
新手友好度
38/100

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