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Implement support for Markdown preview in TextEditorActivity
Uses Commonmark for Markdown parsing and rendering. Due to the way Commonmark works, it cannot support content streaming and update in realtime; user needs to let TextEditorActivity to load as much content as wish.
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21 files changed

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-53
lines changed

21 files changed

+697
-53
lines changed

‎app/build.gradle‎

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@@ -261,6 +261,10 @@ dependencies {
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implementation libs.gson
263263
implementation libs.amaze.trashBin
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implementation libs.commonmark
266+
implementation libs.commonmark.ext.gfm.tables
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implementation libs.commonmark.ext.gfm.strikethrough
264268
}
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kotlin {

‎app/src/main/java/com/amaze/filemanager/asynchronous/asynctasks/texteditor/read/FileWindowReader.kt‎

Lines changed: 10 additions & 11 deletions
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@@ -64,6 +64,7 @@ class FileWindowReader(
6464
* 4. Snaps the end to the last newline (unless at file end)
6565
* 5. Returns the decoded string and actual byte range consumed
6666
*/
67+
@Suppress("LongMethod")
6768
fun readWindow(
6869
byteOffset: Long,
6970
maxChars: Int,
@@ -161,7 +162,7 @@ class FileWindowReader(
161162
* past any continuation bytes (10xxxxxx pattern).
162163
*/
163164
private fun snapToCharBoundary(offset: Long): Long {
164-
if (offset <= 0L || offset >= fileSize) return offset.coerceIn(0L, fileSize)
165+
if (offset !in 1..<fileSize) return offset.coerceIn(0L, fileSize)
165166

166167
val buf = ByteBuffer.allocate(1)
167168
var pos = offset
@@ -226,16 +227,14 @@ class FileWindowReader(
226227
channel = channel,
227228
fileSize = size,
228229
closeable =
229-
object : Closeable {
230-
override fun close() {
231-
try {
232-
fis.close()
233-
} catch (_: Exception) {
234-
}
235-
try {
236-
pfd.close()
237-
} catch (_: Exception) {
238-
}
230+
Closeable {
231+
try {
232+
fis.close()
233+
} catch (_: Exception) {
234+
}
235+
try {
236+
pfd.close()
237+
} catch (_: Exception) {
239238
}
240239
},
241240
)

‎app/src/main/java/com/amaze/filemanager/asynchronous/asynctasks/texteditor/read/ReadTextFileCallable.java‎

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Original file line numberDiff line numberDiff line change
@@ -45,7 +45,7 @@
4545

4646
public class ReadTextFileCallable implements Callable<ReturnedValueOnReadFile> {
4747

48-
public static final int MAX_FILE_SIZE_CHARS = 50 * 1024;
48+
public static final int MAX_FILE_SIZE_CHARS = 100 * 1024;
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5050
private final ContentResolver contentResolver;
5151
private final EditableFileAbstraction fileAbstraction;

‎app/src/main/java/com/amaze/filemanager/ui/activities/texteditor/MarkdownHtmlGenerator.kt‎

Lines changed: 97 additions & 0 deletions
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@@ -0,0 +1,97 @@
1+
/*
2+
* Copyright (C) 2014-2024 Arpit Khurana <arpitkh96@gmail.com>, Vishal Nehra <vishalmeham2@gmail.com>,
3+
* Emmanuel Messulam<emmanuelbendavid@gmail.com>, Raymond Lai <airwave209gt at gmail.com> and Contributors.
4+
*
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* This file is part of Amaze File Manager.
6+
*
7+
* Amaze File Manager is free software: you can redistribute it and/or modify
8+
* it under the terms of the GNU General Public License as published by
9+
* the Free Software Foundation, either version 3 of the License, or
10+
* (at your option) any later version.
11+
*
12+
* This program is distributed in the hope that it will be useful,
13+
* but WITHOUT ANY WARRANTY; without even the implied warranty of
14+
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15+
* GNU General Public License for more details.
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*
17+
* You should have received a copy of the GNU General Public License
18+
* along with this program. If not, see <http://www.gnu.org/licenses/>.
19+
*/
20+
21+
package com.amaze.filemanager.ui.activities.texteditor
22+
23+
import org.commonmark.ext.gfm.strikethrough.StrikethroughExtension
24+
import org.commonmark.ext.gfm.tables.TablesExtension
25+
import org.commonmark.parser.Parser
26+
import org.commonmark.renderer.html.HtmlRenderer
27+
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/**
29+
* Utility for Markdown preview in the text editor.
30+
* Pure functions with no Android dependencies — easy to unit-test.
31+
*/
32+
object MarkdownHtmlGenerator {
33+
/**
34+
* Returns `true` if [fileName] ends with `.md` or `.markdown` (case-insensitive).
35+
*/
36+
@JvmStatic
37+
fun isMarkdownFile(fileName: String?): Boolean {
38+
if (fileName == null) return false
39+
val lower = fileName.lowercase()
40+
return lower.endsWith(".md") || lower.endsWith(".markdown")
41+
}
42+
43+
/**
44+
* Parse Markdown source text and return the rendered HTML body fragment.
45+
*/
46+
@JvmStatic
47+
fun renderToHtml(markdownSource: String): String {
48+
val extensions = listOf(TablesExtension.create(), StrikethroughExtension.create())
49+
val parser = Parser.builder().extensions(extensions).build()
50+
val document = parser.parse(markdownSource)
51+
val renderer = HtmlRenderer.builder().extensions(extensions).build()
52+
return renderer.render(document)
53+
}
54+
55+
/**
56+
* Wrap an HTML body fragment with a full HTML document including theme-aware CSS.
57+
*
58+
* FIXME: Move template to strings.xml
59+
* FIXME: Use Android/Material native Color constants for easy maintenance
60+
*
61+
* @param bodyHtml the rendered Markdown HTML fragment
62+
* @param isDarkTheme true for dark/black theme, false for light theme
63+
* @return a complete HTML document string
64+
*/
65+
@JvmStatic
66+
fun wrapWithBaseHtml(
67+
bodyHtml: String,
68+
isDarkTheme: Boolean,
69+
): String {
70+
val bgColor = if (isDarkTheme) "#1a1a1a" else "#ffffff"
71+
val textColor = if (isDarkTheme) "#e0e0e0" else "#212121"
72+
val linkColor = if (isDarkTheme) "#82b1ff" else "#1565c0"
73+
val codeBg = if (isDarkTheme) "#2d2d2d" else "#f5f5f5"
74+
val borderColor = if (isDarkTheme) "#444444" else "#dddddd"
75+
val quoteColor = if (isDarkTheme) "#aaaaaa" else "#666666"
76+
77+
return """<!DOCTYPE html>
78+
<html><head><meta charset="UTF-8">
79+
<meta name="viewport" content="width=device-width, initial-scale=1.0">
80+
<style>
81+
body { font-family: sans-serif; padding: 16px; margin: 0; background-color: $bgColor; color: $textColor; line-height: 1.6; word-wrap: break-word; }
82+
a { color: $linkColor; }
83+
pre { background-color: $codeBg; padding: 12px; border-radius: 4px; overflow-x: auto; }
84+
code { background-color: $codeBg; padding: 2px 4px; border-radius: 2px; font-size: 90%; }
85+
pre code { padding: 0; background: none; }
86+
blockquote { border-left: 4px solid $borderColor; margin: 0; padding: 0 16px; color: $quoteColor; }
87+
table { border-collapse: collapse; width: 100%; }
88+
th, td { border: 1px solid $borderColor; padding: 8px; text-align: left; }
89+
th { background-color: $codeBg; }
90+
img { max-width: 100%; height: auto; }
91+
hr { border: none; border-top: 1px solid $borderColor; }
92+
h1, h2, h3, h4, h5, h6 { margin-top: 24px; margin-bottom: 16px; }
93+
</style></head><body>
94+
$bodyHtml
95+
</body></html>"""
96+
}
97+
}

‎app/src/main/java/com/amaze/filemanager/ui/activities/texteditor/TextEditorActivity.java‎

Lines changed: 63 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -66,6 +66,7 @@
6666
import android.view.animation.AnimationUtils;
6767
import android.view.inputmethod.EditorInfo;
6868
import android.view.inputmethod.InputMethodManager;
69+
import android.webkit.WebView;
6970
import android.widget.ScrollView;
7071
import android.widget.Toast;
7172

@@ -86,12 +87,14 @@ public class TextEditorActivity extends ThemedActivity
8687
private Typeface inputTypefaceMono;
8788
private androidx.appcompat.widget.Toolbar toolbar;
8889
ScrollView scrollView;
90+
private WebView markdownWebView;
8991

9092
private SearchTextTask searchTextTask;
9193
private static final String KEY_MODIFIED_TEXT = "modified";
9294
private static final String KEY_INDEX = "index";
9395
private static final String KEY_ORIGINAL_TEXT = "original";
9496
private static final String KEY_MONOFONT = "monofont";
97+
private static final String KEY_MARKDOWN_PREVIEW = "markdown_preview";
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9699
private ConstraintLayout searchViewLayout;
97100
public AppCompatImageButton upButton;
@@ -134,6 +137,8 @@ public void onCreate(Bundle savedInstanceState) {
134137
}
135138
mainTextView = findViewById(R.id.textEditorMainEditText);
136139
scrollView = findViewById(R.id.textEditorScrollView);
140+
markdownWebView = findViewById(R.id.textEditorMarkdownWebView);
141+
markdownWebView.getSettings().setJavaScriptEnabled(false);
137142

138143
final Uri uri = getIntent().getData();
139144
if (uri != null) {
@@ -178,6 +183,11 @@ public void onCreate(Bundle savedInstanceState) {
178183
if (savedInstanceState.getBoolean(KEY_MONOFONT)) {
179184
mainTextView.setTypeface(inputTypefaceMono);
180185
}
186+
// Restore markdown preview state
187+
if (savedInstanceState.getBoolean(KEY_MARKDOWN_PREVIEW, false)) {
188+
viewModel.setMarkdownPreviewEnabled(true);
189+
toggleMarkdownPreview(true);
190+
}
181191
// Restore windowed mode state after rotation
182192
if (viewModel.isWindowed()) {
183193
setReadOnly();
@@ -203,6 +213,7 @@ protected void onSaveInstanceState(@NonNull Bundle outState) {
203213
outState.putInt(KEY_INDEX, mainTextView.getScrollY());
204214
outState.putString(KEY_ORIGINAL_TEXT, viewModel.getOriginal());
205215
outState.putBoolean(KEY_MONOFONT, inputTypefaceMono.equals(mainTextView.getTypeface()));
216+
outState.putBoolean(KEY_MARKDOWN_PREVIEW, viewModel.getMarkdownPreviewEnabled());
206217
}
207218

208219
private void checkUnsavedChanges() {
@@ -309,6 +320,11 @@ public boolean onPrepareOptionsMenu(Menu menu) {
309320
// Hide search in windowed mode (search only works on in-memory text)
310321
menu.findItem(R.id.find).setVisible(!windowed);
311322

323+
// Show markdown preview item only for .md/.markdown files
324+
MenuItem markdownItem = menu.findItem(R.id.markdown_preview);
325+
markdownItem.setVisible(isMarkdownFile());
326+
markdownItem.setChecked(viewModel.getMarkdownPreviewEnabled());
327+
312328
menu.findItem(R.id.monofont).setChecked(inputTypefaceMono.equals(mainTextView.getTypeface()));
313329
return super.onPrepareOptionsMenu(menu);
314330
}
@@ -362,6 +378,11 @@ public boolean onOptionsItemSelected(MenuItem item) {
362378
} else if (item.getItemId() == R.id.monofont) {
363379
item.setChecked(!item.isChecked());
364380
mainTextView.setTypeface(item.isChecked() ? inputTypefaceMono : inputTypefaceDefault);
381+
} else if (item.getItemId() == R.id.markdown_preview) {
382+
boolean newState = !item.isChecked();
383+
item.setChecked(newState);
384+
viewModel.setMarkdownPreviewEnabled(newState);
385+
toggleMarkdownPreview(newState);
365386
} else {
366387
return false;
367388
}
@@ -661,7 +682,6 @@ private void observeWindowContent() {
661682

662683
// Determine an anchor: find the text line near the middle of the current viewport
663684
int oldScrollY = scrollView.getScrollY();
664-
Layout oldLayout = mainTextView.getLayout();
665685

666686
// Replace text (TextWatcher will fire but windowed-mode guard skips modification
667687
// tracking)
@@ -673,7 +693,6 @@ private void observeWindowContent() {
673693
Layout newLayout = mainTextView.getLayout();
674694
if (newLayout == null) return;
675695

676-
TextEditorActivityViewModel.Direction direction;
677696
// Infer direction from old scroll position
678697
int viewportHeight = scrollView.getHeight();
679698
if (oldScrollY > viewportHeight / 2) {
@@ -728,4 +747,46 @@ public void initWindowedScrollListener() {
728747

729748
scrollView.getViewTreeObserver().addOnScrollChangedListener(windowedScrollListener);
730749
}
750+
751+
// ── Markdown Preview Helpers ────────────────────────────────────────
752+
753+
/** Returns true if the currently opened file has a Markdown extension (.md or .markdown). */
754+
private boolean isMarkdownFile() {
755+
EditableFileAbstraction file = viewModel.getFile();
756+
if (file == null) return false;
757+
return MarkdownHtmlGenerator.isMarkdownFile(file.name);
758+
}
759+
760+
/**
761+
* Toggle between Markdown preview (WebView) and the normal EditText editor.
762+
*
763+
* @param enabled true to show the WebView with rendered Markdown; false to show EditText
764+
*/
765+
private void toggleMarkdownPreview(boolean enabled) {
766+
if (enabled) {
767+
renderMarkdownToWebView();
768+
scrollView.setVisibility(View.GONE);
769+
markdownWebView.setVisibility(View.VISIBLE);
770+
} else {
771+
markdownWebView.setVisibility(View.GONE);
772+
scrollView.setVisibility(View.VISIBLE);
773+
}
774+
invalidateOptionsMenu();
775+
}
776+
777+
/**
778+
* Parse the current EditText content as Markdown using commonmark, render to HTML, and load it
779+
* into the WebView.
780+
*/
781+
private void renderMarkdownToWebView() {
782+
String markdownSource = "";
783+
if (mainTextView.getText() != null) {
784+
markdownSource = mainTextView.getText().toString();
785+
}
786+
787+
String bodyHtml = MarkdownHtmlGenerator.renderToHtml(markdownSource);
788+
boolean isDark = getAppTheme().equals(AppTheme.DARK) || getAppTheme().equals(AppTheme.BLACK);
789+
String fullHtml = MarkdownHtmlGenerator.wrapWithBaseHtml(bodyHtml, isDark);
790+
markdownWebView.loadDataWithBaseURL(null, fullHtml, "text/html", "UTF-8", null);
791+
}
731792
}

‎app/src/main/java/com/amaze/filemanager/ui/activities/texteditor/TextEditorActivityViewModel.kt‎

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Original file line numberDiff line numberDiff line change
@@ -66,6 +66,11 @@ class TextEditorActivityViewModel : ViewModel() {
6666

6767
var file: EditableFileAbstraction? = null
6868

69+
// ── Markdown preview state ────────────────────────────────────────
70+
71+
/** Whether Markdown preview mode is currently enabled. */
72+
var markdownPreviewEnabled = false
73+
6974
// ── Sliding window state ──────────────────────────────────────────
7075

7176
/** Whether the editor is in windowed (read-only) mode for large files. */

‎app/src/main/res/layout/search.xml‎

Lines changed: 27 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -43,23 +43,36 @@
4343

4444
</LinearLayout>
4545

46-
<ScrollView
47-
android:id="@+id/textEditorScrollView"
46+
<FrameLayout
47+
android:id="@+id/textEditorContentFrame"
4848
android:layout_width="match_parent"
49-
android:layout_height="match_parent"
50-
android:fillViewport="true">
49+
android:layout_height="match_parent">
5150

52-
<androidx.appcompat.widget.AppCompatEditText
53-
android:id="@+id/textEditorMainEditText"
51+
<ScrollView
52+
android:id="@+id/textEditorScrollView"
5453
android:layout_width="match_parent"
55-
android:layout_height="wrap_content"
56-
android:fontFamily="sans-serif-light"
57-
android:gravity="start|top"
58-
android:inputType="textCapSentences|textMultiLine"
59-
android:lineSpacingExtra="1dp"
60-
android:padding="16dp"
61-
android:textSize="14sp" />
54+
android:layout_height="match_parent"
55+
android:fillViewport="true">
6256

63-
</ScrollView>
57+
<androidx.appcompat.widget.AppCompatEditText
58+
android:id="@+id/textEditorMainEditText"
59+
android:layout_width="match_parent"
60+
android:layout_height="wrap_content"
61+
android:fontFamily="sans-serif-light"
62+
android:gravity="start|top"
63+
android:inputType="textCapSentences|textMultiLine"
64+
android:lineSpacingExtra="1dp"
65+
android:padding="16dp"
66+
android:textSize="14sp" />
67+
68+
</ScrollView>
69+
70+
<WebView
71+
android:id="@+id/textEditorMarkdownWebView"
72+
android:layout_width="match_parent"
73+
android:layout_height="match_parent"
74+
android:visibility="gone" />
75+
76+
</FrameLayout>
6477

6578
</androidx.appcompat.widget.LinearLayoutCompat>

‎app/src/main/res/menu/text.xml‎

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -42,4 +42,10 @@
4242
android:title="@string/monofont"
4343
android:checkable="true"
4444
app:showAsAction="never" />
45+
<item
46+
android:id="@+id/markdown_preview"
47+
android:title="@string/markdown_preview"
48+
android:checkable="true"
49+
android:visible="false"
50+
app:showAsAction="never" />
4551
</menu>

‎app/src/main/res/values-ja/strings.xml‎

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Original file line numberDiff line numberDiff line change
@@ -479,6 +479,7 @@
479479
<string name="copy_low_memory">メモリ不足。メモリを解放してください</string>
480480
<string name="cloud_token_lost">トークンを失われた。もう一度サインインしてください。</string>
481481
<string name="monofont">等幅フォント</string>
482+
<string name="markdown_preview">Markdown プレビュー</string>
482483
<string name="showHeaders">ヘッダーを表示する</string>
483484

484485
<!--FROM HERE ON STRINGS ARE EXCLUSIVELY USED IN plurals.xml-->

‎app/src/main/res/values-uk/strings.xml‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -479,6 +479,7 @@
479479
<string name="copy_low_memory">Не вистачає пам\'яті, будь ласка звільніть оперативну пам\'ять</string>
480480
<string name="cloud_token_lost">Token втрачено, будь ласка авторизуйтесь знову</string>
481481
<string name="monofont">Моноширинний шрифт</string>
482+
<string name="markdown_preview">Попередній перегляд Markdown</string>
482483
<string name="showHeaders">Відображати заголовки</string>
483484

484485
<!--FROM HERE ON STRINGS ARE EXCLUSIVELY USED IN plurals.xml-->

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