Is it possible to set a custom font for entire of application?

Question

I need to use certain font for my entire application. I have .ttf file for the same. Is it possible to set this as default font, at application start up and then use it else

Answer 1

I would like to improve weston's answer for API 21 Android 5.0.

Cause

Under API 21, most of the text styles include fontFamily setting, like:

Which applys the default Roboto Regular font:

sans-serif

The original answer fails to apply monospace font, because android:fontFamily has greater priority to android:typeface attribute (reference). Using Theme.Holo.* is a valid workaround, because there is no android:fontFamily settings inside.

Solution

Since Android 5.0 put system typeface in static variable Typeface.sSystemFontMap (reference), we can use the same reflection technique to replace it:

protected static void replaceFont(String staticTypefaceFieldName,
        final Typeface newTypeface) {
    if (isVersionGreaterOrEqualToLollipop()) {
        Map newMap = new HashMap();
        newMap.put("sans-serif", newTypeface);
        try {
            final Field staticField = Typeface.class
                    .getDeclaredField("sSystemFontMap");
            staticField.setAccessible(true);
            staticField.set(null, newMap);
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
    } else {
        try {
            final Field staticField = Typeface.class
                    .getDeclaredField(staticTypefaceFieldName);
            staticField.setAccessible(true);
            staticField.set(null, newTypeface);
        } catch (NoSuchFieldException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
    }
}