Java：找不到符号类

Question

我正在编写一个程序，它从两个文本字段中获取两个值并计算它们的结果。

问题是Java编辑器向我显示以下错误：

cannot find symbol class EditText
cannot find symbol class Button
cannot find symbol class string
cannot find symbol class variable integer
cannot find symbol class integer

这是我的代码：

public class MainActivity extends AppCompatActivity
{
    EditText firstNumber;
    EditText secondNumber;
    Button btnAdd;
    TextView total;


    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        firstNumber = (EditText)findViewById(R.id.firstNumber);
        secondNumber = (EditText)findViewById(R.id.secondNumber);
        btnAdd = (Button)findViewById(R.id.btnAdd);
        total = (TextView)findViewById(R.id.total);
  }

    public void btnAdd_Click(View view)
    {
        string getfirstNumber = firstNumber.getText().toString();
        string getsecondNumber = secondNumber.getText().toString();
integer totalResult = integer.parseInt(getfirstNumber) + integer.parseInt(getsecondNumber);
total.setText("Total = " + integer.toString(totalResult));

    }
}

Answer 1

使用以下导入

import android.widget.Button;
import android.widget.EditText;