如何将用户输入到EditText字段中

I am building a larger app and I made this small one just to figure out how to accomplish getting text from user input however it is not working. If I create a string reference at the Text property of my EditText field it works ok. If I leave it blank and enter the text into the field when the application runs in my emulator it does not work. Any ideas. I am building a larger app and I made this smal