[Android] Support for images inside HTML label

[kubaflo]

Description of Change

    <Label TextType="Html">
        <![CDATA[
            <h1>Hello World</h1>
            <img src="https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcS7invFYnW6Ntqiibf_nRumE0-BilpyjTMJTDVEtXbPHw&s" alt="eiffel">
            <img src="https://img-prod-cms-rt-microsoft-com.akamaized.net/cms/api/am/imageFileData/RWCZER?ver=1433&q=90&m=6&h=195&w=348&b=%23FFFFFFFF&l=f&o=t&aim=true" alt="eiffel">
        ]]>
    </Label>

Before	After

Issues Fixed

Fixes #21044

[kubaflo]

This class could be potentially moved to this file: maui/src/Core/AndroidNative/maui/src/main/java/com/microsoft/maui/PlatformInterop.java to improve performance if this PR makes sense

[rmarinho]

/azp run MAUI-UITests-public

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jsuarezruiz]

I know images already works on iOS and this change align the behavior. Not sure about the Windows behavior, did you try?

[kubaflo]

I don't have a Windows device. Maybe you could have a look at it, please?

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 21679

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 21679"

[Copilot]

Pull request overview

Adds Android support for rendering <img> tags when Label.TextType="Html" by wiring an Html.IImageGetter into the Android HTML parsing path so images can be fetched and inserted into the resulting spannable text.

Changes:

• Updated Android TextViewExtensions.UpdateTextHtml to use Html.FromHtml(..., imageGetter: ...) on API 24+ and re-apply text when images complete loading.
• Introduced an Android ImageGetter implementation that downloads images via HttpClient, caches them, and triggers a text refresh once loaded.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 9 comments.

File	Description
src/Core/src/Platform/Android/TextViewExtensions.cs	Uses Html.IImageGetter during HTML parsing and re-applies text to surface loaded images.
src/Core/src/Platform/Android/ImageGetter.cs	Implements image download + caching for <img src="..."> used by Android HTML parsing.

[Copilot]

Bitmaps is a static Dictionary that retains BitmapDrawables indefinitely and never disposes them; this can grow unbounded (e.g., chat feeds with many unique emoji URLs) and lead to OOMs. Consider replacing this with a bounded cache (e.g., LruCache keyed by URL) and disposing/evicting bitmaps when the cache is full, or otherwise providing a way to clear the cache when no longer needed.

[Copilot]

The catch block is empty, which will silently hide network/decode failures and make it very hard to diagnose why images aren’t showing. Consider at least logging the exception (or propagating it through a callback) so app developers can troubleshoot invalid URLs, TLS issues, etc.

[Copilot]

Each successfully loaded image triggers SetTextHtml(), which reparses the entire HTML and resets the TextView text. With multiple tags this can cause repeated full re-parses and UI churn. Consider updating only the affected span/drawable (or batching updates) to avoid O(N images) full re-renders.

Suggested change

	{
	var htmlText = WebUtility.HtmlDecode(text);
	if (OperatingSystem.IsAndroidVersionAtLeast(24))
	textView.SetText(Html.FromHtml(htmlText, FromHtmlOptions.ModeCompact), BufferType.Spannable);
	else
	// Track generation to prevent stale image-load callbacks from overwriting newer text
	var generation = s_htmlGenerations.GetOrCreateValue(textView);
	int currentGen = ++generation.Value;
	ImageGetter? imageGetter = null;
	void SetTextHtml()
	{
	if (OperatingSystem.IsAndroidVersionAtLeast(24))
	{
	// Use ImageGetter to load images, but avoid recursively reparsing the HTML on each image load.
	// The callback simply invalidates and re-layouts the existing TextView content.
	textView.SetText(
	Html.FromHtml(
	htmlText,
	FromHtmlOptions.ModeCompact,
	imageGetter: new ImageGetter(() =>
	{
	textView.Invalidate();
	textView.RequestLayout();
	}),
	tagHandler: null),
	BufferType.Spannable);
	}
	else
	{
	#pragma warning disable CS0618 // Type or member is obsolete
	textView.SetText(Html.FromHtml(htmlText), BufferType.Spannable);
	#pragma warning restore CS0618 // Type or member is obsolete
	}

[kubaflo]

🔍 Manual Testing Review — PR #21679

Test Setup

Rebuilt and deployed the HostApp on both Android emulator and iOS simulator (iPhone Xs) using the XAML-based test page from the PR description:

<Label TextType="Html"><![CDATA[
    <h1>Hello World</h1>
    <img src="https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcS7invFYnW6Ntqiibf_nRumE0-BilpyjTMJTDVEtXbPHw&s" alt="eiffel">
    <img src="https://img-prod-cms-rt-microsoft-com.akamaized.net/cms/api/am/imageFileData/RWCZER?ver=1433&q=90&m=6&h=195&w=348&b=%23FFFFFFFF&l=f&o=t&aim=true" alt="dotnet">
]]></Label>

Results

Platform	Images Rendered	Notes
iOS (iPhone Xs, iOS 18.5)	✅	Images display correctly out-of-the-box (iOS handles HTML img natively)
Android (API 34 emulator)	✅	Images load and display after async download via the new ImageGetter — confirms the fix works

Code Review Notes

What the PR does well:

• ✅ Clean Html.IImageGetter implementation with async download + cache
• ✅ Generation tracking via ConditionalWeakTable to prevent stale callbacks from overwriting newer text
• ✅ Sensible limits: 10 MB per image, 50-entry cache, 30s timeout
• ✅ Proper error handling with Log.Warn diagnostics

Observations / things to consider:

1. Static HttpClient & cache — s_httpClient and s_cache are static, meaning they persist for the app lifetime. This is fine for most apps, but very image-heavy HTML labels could accumulate memory. The 50-entry eviction helps but recycled Bitmap objects may still hold native memory briefly.
2. WebUtility.HtmlDecode on the full HTML — This decodes & → & etc. before passing to Html.FromHtml. For most cases this is correct, but if the HTML itself contains entities intentionally (e.g., <code>), double-decoding could alter content. Worth verifying with edge-case HTML.
3. No cancellation on navigation — If a user navigates away while images are downloading, the LoadImageAsync fire-and-forget will still complete and cache. Not a bug, but something to be aware of.
4. Missing test coverage — The PR adds no automated UI test for this scenario. Consider adding a test in TestCases.HostApp/Issues/ + TestCases.Shared.Tests/Tests/Issues/ to prevent regression.

Verdict

✅ Fix confirmed working on both platforms. The approach is solid and well-structured. Would recommend adding a UI test before merge.

[kubaflo]

📋 Pre-Merge Review — PR #21679

Title/Description

• Title is clear: [Android] Support for images inside HTML label ✅
• Description needs the required NOTE block for testing PR builds
• Root cause not explained in description — Android's Html.FromHtml() was called without an Html.IImageGetter, so <img> tags rendered as empty boxes

Code Review (2 files changed, +154/-4)

ImageGetter.cs (new file)

• ✅ Clean Html.IImageGetter implementation with async HTTP download
• ✅ Shared static HttpClient (no per-request allocation)
• ✅ BitmapDrawable(Resources, bitmap) — density-aware constructor
• ✅ Bounded cache (50-entry LRU with bitmap recycling)
• ✅ Sensible limits: 10 MB per image, 30s timeout
• ✅ async Task instead of async void (safer exception handling)
• ✅ Concurrent fetch deduplication via s_inFlight
• ✅ Error logging with Log.Warn for diagnostics

TextViewExtensions.cs (modified)

• ✅ Passes ImageGetter to Html.FromHtml() on both API 24+ and legacy code paths
• ✅ Generation tracking via ConditionalWeakTable prevents stale image-load callbacks

Items to Address Before Merge

1. ⚠️ Missing NOTE block in PR description (required for all PRs)
2. ⚠️ Missing UI test — No automated test for HTML image rendering. Should add Issue21044 HostApp page + NUnit test to prevent regression
3. ℹ️ No PublicAPI changes needed — ImageGetter is internal

Manual Testing Results

• ✅ iOS: Images display correctly (native behavior)
• ✅ Android: Images load and render after async download — fix confirmed working

Verdict

✅ Code is solid and well-structured. Address the missing test coverage and NOTE block before merge.