This is what I use when I want to enable the user to change the text size / zoom in a WebView:
private WebView mWebView;
// init web view and stuff like that ...
private void textSmaller() {
WebSettings settings = mWebView.getSettings();
settings.setTextZoom(settings.getTextZoom() - 10);
}
private void textBigger() {
WebSettings settings = mWebView.getSettings();
settings.setTextZoom(settings.getTextZoom() + 10);
}
On Actionbar Item click, I call either textSmaller() or textBigger() to change the text size.