refactor(Region): optimize SelectCity search

[ArgoZhang]

Link issues

fixes #1129

Summary By Copilot

• debounce SelectCity search input to reduce JavaScript/.NET interop calls during continuous typing
• lazily build per-instance province and city pinyin indexes and reuse them for filtering and highlighting
• cache filtered provinces until the search text changes and skip duplicate searches
• add stable render keys for province and city elements
• cover Chinese, pinyin, and cleared searches with component tests

Regression?

• Yes
• No

The public component API, result presentation, and selection behavior remain unchanged.

Risk

• High
• Medium
• Low

The change is isolated to SelectCity search dispatch, filtering, and rendering. Search indexes remain scoped to each component instance so custom service data is not shared across instances.

Verification

• Manual (required)

• Automated

• passed all 4 UnitTestRegion tests on net10.0

• checked SelectCity.razor.js with Node.js syntax validation

• checked the branch diff for whitespace errors

Packaging changes reviewed?

• Yes
• No
• N/A

☑️ Self Check before Merge

⚠️ Please check all items below before review. ⚠️

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• Merge the latest code from the main branch

Summary by Sourcery

Improve SelectCity search performance while preserving its public API, presentation, and selection behavior.

Enhancements:

• Optimize SelectCity search by reducing interop calls, reusing per-instance search indexes, caching filtered results, and avoiding duplicate searches.
• Add stable rendering keys for province and city entries.

Tests:

• Add component coverage for Chinese, pinyin, and cleared SelectCity searches.

[sourcery-ai]

Reviewer's Guide

SelectCity search now reduces interop and filtering overhead through debouncing, duplicate suppression, and per-instance cached pinyin/filter indexes, while stable render keys preserve UI state and bUnit tests cover Chinese, pinyin, and cleared searches without changing the public API or selection behavior.

Sequence diagram for debounced SelectCity search

sequenceDiagram
    participant User
    participant SearchInput
    participant SelectCityJS
    participant SelectCity

    User->>SearchInput: type search text
    SearchInput->>SelectCityJS: Input.composition
    SelectCityJS->>SelectCityJS: debounce
    alt input is connected and value is unchanged
        SelectCityJS->>SelectCity: invokeMethodAsync(triggerSearch, value)
        SelectCity->>SelectCity: TriggerSearch(value)
        alt search text changed
            SelectCity->>SelectCity: FilterProvinces(searchText)
            SelectCity->>SelectCity: StateHasChanged()
        else duplicate search
            SelectCity-->>SelectCity: return
        end
    end

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Flow diagram for SelectCity search filtering

flowchart TD
    A[Search text received] --> B{Text changed?}
    B -- No --> C[Skip duplicate search]
    B -- Yes --> D[Cache filtered provinces]
    D --> E{Contains Chinese?}
    E -- Yes --> F[Match province and city names]
    E -- No --> G[Build or reuse pinyin indexes]
    G --> H[Match province and city pinyin]
    F --> I[Render filtered provinces]
    H --> I
    I --> J[Reuse pinyin index for city highlighting]

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File-Level Changes

Change	Details	Files
Debounced browser-to-.NET search dispatch and eliminated redundant searches during typing.	Wrapped composition input handling in a debounce callback. Skipped invocation when the input is detached or its value has changed since scheduling. Ignored duplicate normalized search text in the component.	src/components/BootstrapBlazor.Region/Components/SelectCity.razor.js src/components/BootstrapBlazor.Region/Components/SelectCity.razor.cs
Added per-component cached indexes and cached filtered province results for Chinese and pinyin searches.	Lazily generated province and city pinyin indexes scoped to each SelectCity instance. Stored filtered provinces when search text changes and reset them when search is disabled or cleared. Reused the city pinyin index for highlighting matching cities.	src/components/BootstrapBlazor.Region/Components/SelectCity.razor.cs
Improved render stability for dynamically filtered province and city elements.	Added stable Blazor keys to province containers and city list items. Rendered from the cached filtered province collection.	src/components/BootstrapBlazor.Region/Components/SelectCity.razor
Added component-level coverage for Chinese, pinyin, and cleared searches.	Initialized bUnit services and JS interop for SelectCity tests. Verified province filtering, pinyin city highlighting, and restoration of all provinces after clearing search.	test/UnitTestRegion/RegionTest.cs test/UnitTestRegion/UnitTestRegion.csproj

Assessment against linked issues

Issue	Objective	Addressed	Explanation
#1129	Debounce SelectCity search input and avoid duplicate searches and unnecessary JavaScript/.NET interop calls during continuous or unchanged input.	✅
#1129	Lazily build and reuse per-component province and city pinyin indexes, cache filtered provinces until the search text changes, and reuse cached pinyin for filtering and match highlighting.	✅
#1129	Preserve existing presentation and selection behavior while adding stable render keys and automated coverage for Chinese, pinyin, and cleared searches.	✅

Possibly linked issues

• refactor(Region): optimize SelectCity search #1129: The PR directly implements the issue’s requested SelectCity debounce, caching, pinyin reuse, stable keys, and coverage.

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