android - Error on SetTextSize by using settingPreference -

how can set textsize setting preference fragment textview? font size selected listview provide code below image.

please see image below:

i know doing wrong. please show me proper way this.

this font size value:

this listpreference:

<listpreference         android:title="font size"         android:summary="select desirable font size"         android:key="fontsizekey"         android:entries="@array/select_font_size"         android:entryvalues="@array/select_font_size_value"         android:defaultvalue="24"/> 

and if guys have website/tutorial/blogs link me refer, good.

the value textview accept float. 1 more thing value sharedpreference, use key.

string setfontsize  = getsharedpreferences.getstring("fontsizekey"); setduatext = settextsize(float.valueof(setfontsize));