Android CustomTabsIntent how to open html file in assets folder

Question

I want to open html file in assets folder with CustomTabsIntent, but when after call, it is only show Toast and say : "Can not display PDF( Can not open「index.html」)".

How to open a html file with CustomTabsIntent?

CustomTabsIntent.Builder builder = new CustomTabsIntent.Builder();
builder.enableUrlBarHiding();
CustomTabsIntent customTabsIntent = builder.build();
customTabsIntent.intent.setType("text/html");
customTabsIntent.launchUrl(this, Uri.parse("file:///android_asset/index.html"));