How to find android TextView number of characters per line?

Try this:

private boolean isTooLarge (TextView text, String newText) {
    float textWidth = text.getPaint().measureText(newText);
    return (textWidth >= text.getMeasuredWidth ());
}

Detecting how many characters fit will be impossible due to the variable width of the characters. The above function will test if a particular string will fit or not in the TextView. The content of newText should be all the characters in a particular line. If true, then start a new line (and using a new string to pass as parameter).

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Answer to the comment:

1. because the app can be run in many systems is exactly why you need to measure it.
2. This is a way to solve your "overall question". What is the difference between using str.size()>numCol vs is too large? You will need to implement your animation (hint #1: insert a newline character)
3. as I said before when you start a new line, you start a new string (hint #2: if you extend TextView, you can implement all this in overriding setText). (hint #3: Keep track of the lines created with a static int lines; and use newString.split("\\r?\\n")[lines-1] to check for length).

You can get total line of Textview and get string for each characters by below code.Then you can set style to each line whichever you want.

I set first line bold.

private void setLayoutListner( final TextView textView ) {
        textView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                textView.getViewTreeObserver().removeGlobalOnLayoutListener(this);

                final Layout layout = textView.getLayout();

                // Loop over all the lines and do whatever you need with
                // the width of the line
                for (int i = 0; i < layout.getLineCount(); i++) {
                    int end = layout.getLineEnd(0);
                    SpannableString content = new SpannableString( textView.getText().toString() );
                    content.setSpan(new StyleSpan(android.graphics.Typeface.BOLD), 0, end, 0);
                    content.setSpan(new StyleSpan(android.graphics.Typeface.NORMAL), end, content.length(), 0);
                    textView.setText( content );
                }
            }
        });
    }

Try this way.You can apply multiple style this way.