android在点击EditText的时候始终不弹出软件键盘

  EditText et_start_time = (EditText) this.findViewById(R.id.et_start_time);
                int inType = et_start_time.getInputType();
                et_start_time.setInputType(InputType.TYPE_NULL);  
                et_start_time.onTouchEvent(event);
                et_start_time.setInputType(inType);
                et_start_time.setSelection(et_start_time.getText().length());