c# - Split string with height and width on textblock - Silverlight Window phone -

i have long string , want binding textblock limit width , height. caculator height textblock as:

textresult.text = reader.readtoend(); double h = textresult.actualheight; 

if height textblock > height limit, want spit string @ line in textblock have height = height limit , binding rest other textblock. can me?