求助，为什么添加onclicklistener程序就崩溃了呢

代码如下
public class MainActivity extends ActionBarActivity {
EditText text_name;
Spinner spinner_scter;
Spinner spinner_sqter;
Spinner spinner_seday;
DatePicker mDatePicker;
Button btn_save;
Button btn_return;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initdate();
btn_return.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
}
});
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment())
.commit();
}
}
public void initdate(){
text_name=(EditText) this.findViewById(R.id.text_name);
spinner_scter=(Spinner) this.findViewById(R.id.spinner_scter );
spinner_sqter=(Spinner) this.findViewById(R.id.spinner_sqter);
spinner_seday=(Spinner) this.findViewById(R.id.spinner_seday);
mDatePicker=(DatePicker) this.findViewById(R.id.mDatePicker);
btn_save=(Button) this.findViewById(R.id.btn_save);
btn_return=(Button) this.findViewById(R.id.btn_return);
}