Expand Android Selection

Sun Dec 9, 2018 by Bill Farmer. Categories: Hacking .

When editing data or source files it would be useful to have selections triggered by a double tap or long press expand to enclosing delimiters or brackets.

There is a section in the Android docs which explains how to set up your own context menu or contextual action mode, but not how to change the selection.

This method is fine if you have only one text editor view in your app, but would be difficult with more than one as there is no way to identify the originating view. In Java a regular expression (regex) can only search forwards, but not backwards, so we search forwards using a regex, work out what to look for backwards, and use a standard string reverse search to find the start of the extended selection. The regex contains bracket characters and quote characters. If the forward search finds an opening bracket, we don’t change the selection. If the extended selection contains a newline we don’t change the selection because we have probably got a closing quote on one line and an opening quote on another. If the delimiter is a semicolon we look back for a newline.


    public final static String PATTERN_CHARS =
        "[\\(\\)\\[\\]\\{\\}\\<\\>\"'`]";
    public final static String INVALID_CHARS = "([{<";

    // onActionModeStarted
    @Override
    public void onActionModeStarted(ActionMode mode)
    {
        super.onActionModeStarted(mode);

        // If there's a file
        if (file != null)
        {
            // Get the mime type
            String type = FileUtils.getMimeType(file);
            // If the type is unknown or not text/plain
            if (type == null || !type.equals(TEXT_PLAIN))
            {
                // Get the start and end of the selection
                int start = textView.getSelectionStart();
                int end = textView.getSelectionEnd();
                // And the text
                String text = textView.getText().toString();

                // Get a pattern and a matcher for delimiter
                // characters
                Pattern pattern =
                    Pattern.compile(PATTERN_CHARS);
                Matcher matcher =
                    pattern.matcher(text);

                // Find the first match after the end of the selection
                if (matcher.find(end))
                {
                    // Update the selection end
                    end = matcher.start();

                    // Get the matched char
                    char c = text.charAt(end);

                    // Check for opening brackets
                    if (INVALID_CHARS.indexOf(c) == -1)
                    {
                        switch (c)
                        {
                            // Check for close brackets and look for
                            // the open brackets
                        case ')':
                            c = '(';
                            break;

                        case ']':
                            c = '[';
                            break;

                        case '}':
                            c = '{';
                            break;

                        case '>':
                            c = '<';
                            break;
                        }

                        // Do reverse search
                        start = text.lastIndexOf(c, start) + 1;

                        // Check for included newline
                        if (start > text.lastIndexOf('\n', end))
                            // Update selection
                            textView.setSelection(start, end);
                    }
                }
            }
        }
    }

Bill Farmer

Expand Android Selection

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