Editor 4.2.0
Markdown editing highlight for Android based on Markwon.
Getting started with editor
// obtain Markwon instance
final Markwon markwon = Markwon.create(this);
// create editor
final MarkwonEditor editor = MarkwonEditor.create(markwon);
// set edit listener
editText.addTextChangedListener(MarkwonEditorTextWatcher.withProcess(editor));
The code above highlights in-place which is OK for relatively small markdown inputs.
If you wish to offload main thread and highlight in background use withPreRender MarkwonEditorTextWatcher:
editText.addTextChangedListener(MarkwonEditorTextWatcher.withPreRender(
editor,
Executors.newCachedThreadPool(),
editText));
MarkwonEditorTextWatcher automatically triggers markdown highlight when text in EditText changes.
But you still can invoke MarkwonEditor manually:
editor.process(editText.getText());
// please note that MarkwonEditor operates on caller thread,
// if you wish to execute this operation in background - this method
// must be called from background thread
editor.preRender(editText.getText(), new MarkwonEditor.PreRenderResultListener() {
@Override
public void onPreRenderResult(@NonNull MarkwonEditor.PreRenderResult result) {
// it's wise to check if rendered result is for the same input,
// for example by matching raw input
if (editText.getText().toString().equals(result.resultEditable().toString())) {
// if you are in background thread do not forget
// to execute dispatch in main thread
result.dispatchTo(editText.getText());
}
}
});
Implementation Detail
It must be mentioned that highlight is implemented via text diff. Everything that is present in raw markdown input but missing from rendered result is considered to be punctuation.
Tables and LaTeX
Tables and LaTeX nodes won't be rendered correctly. They will be treated as punctuation as whole. This comes from their implementation - they are mocked and do not present in final result as text and thus cannot be diffed.
Custom punctuation span
By default MarkwonEditor uses lighter text color of widget to customize punctuation.
If you wish to use a different span you can use punctuationSpan configuration step:
final MarkwonEditor editor = MarkwonEditor.builder(Markwon.create(this))
.punctuationSpan(CustomPunctuationSpan.class, CustomPunctuationSpan::new)
.build();
public class CustomPunctuationSpan extends ForegroundColorSpan {
CustomPunctuationSpan() {
super(0xFFFF0000); // RED
}
}
Additional handling
In order to additionally highlight portions of markdown input (for example make text wrapped with **
symbols bold) EditHandler can be used:
final MarkwonEditor editor = MarkwonEditor.builder(Markwon.create(this))
.useEditHandler(new AbstractEditHandler<StrongEmphasisSpan>() {
@Override
public void configurePersistedSpans(@NonNull PersistedSpans.Builder builder) {
// Here we define which span is _persisted_ in EditText, it is not removed
// from EditText between text changes, but instead - reused (by changing
// position). Consider it as a cache for spans. We could use `StrongEmphasisSpan`
// here also, but I chose Bold to indicate that this span is not the same
// as in off-screen rendered markdown
builder.persistSpan(Bold.class, Bold::new);
}
@Override
public void handleMarkdownSpan(
@NonNull PersistedSpans persistedSpans,
@NonNull Editable editable,
@NonNull String input,
@NonNull StrongEmphasisSpan span,
int spanStart,
int spanTextLength) {
// Unfortunately we cannot hardcode delimiters length here (aka spanTextLength + 4)
// because multiple inline markdown nodes can refer to the same text.
// For example, `**_~~hey~~_**` - we will receive `**_~~` in this method,
// and thus will have to manually find actual position in raw user input
final MarkwonEditorUtils.Match match =
MarkwonEditorUtils.findDelimited(input, spanStart, "**", "__");
if (match != null) {
editable.setSpan(
// we handle StrongEmphasisSpan and represent it with Bold in EditText
// we still could use StrongEmphasisSpan, but it must be accessed
// via persistedSpans
persistedSpans.get(Bold.class),
match.start(),
match.end(),
Spanned.SPAN_EXCLUSIVE_EXCLUSIVE
);
}
}
@NonNull
@Override
public Class<StrongEmphasisSpan> markdownSpanType() {
return StrongEmphasisSpan.class;
}
})
.build();