Flutter TextField set default value Default value and the cursor position

The main controller implemented by the specific code as follows

TextField(
　　　　　　　　　　//输入键盘类型
              keyboardType: TextInputType.text,
              autofocus: true,
              decoration: InputDecoration(
                border: OutlineInputBorder(
                    borderRadius: BorderRadius.circular(30),
                    borderSide: BorderSide.none),
              ),
              onChanged: (value) {
                this._keyword = value;
              },
              controller: TextEditingController.fromValue(TextEditingValue(
                  text: '${this._keyword == null ? "" : this._keyword}',  //Determining whether the keyword is empty 
                  // remains at the last cursor 

                  Selection: TextSelection.fromPosition (TextPosition ( 
                      Affinity: TextAffinity.downstream, 
                      offset: ' $ {} this._keyword ' .length)))), 
            ),