最终变量的范围对OnClickListener不可见

Question

I am a beginner, I'm trying to build a calculator. I have a problem.

I write the answer like this:

ans += Double.parseDouble(etResult.getText().toString());
outTest.setText("The answer is " + ans);

This is in an OnClickListenter. The problem is that I have to communicate with the double ans, which I defined in the beginning of my project, if I want to communicate with the double I need him to be final, but if he is final I cant change him in the OnClickListener.

Can anyone help me and tell me how can I do this? thanks.

Answer 1

使用通常的技巧：代替double ans = 0声明final double[] ans = {0} ，然后可以在处理程序代码中使用ans[0] += ...

Answer 2

You can writ your code as follows

public class TestActivity extends Activity {
/** Called when the activity is first created. */
Double dbl;
Button btn;
EditText et;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    btn = (Button) findViewById(R.id.button1);
    et = (EditText) findViewById(R.id.editText1);
    btn.setOnClickListener(new OnClickListener() {

        public void onClick(View arg0) {
            // TODO Auto-generated method stub
            dbl = Double.parseDouble(et.getText().toString());
            Log.e("double", "" + dbl);
        }
    });
}

}

Answer 3

Try it

public class TestActivity extends Activity {
/** Called when the activity is first created. */
Double dbl;
Button btn;
EditText et1, et2;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    btn = (Button) findViewById(R.id.button1);
    et1 = (EditText) findViewById(R.id.editText1);
    et2 = (EditText) findViewById(R.id.editText2);
    btn.setOnClickListener(new OnClickListener() {

        public void onClick(View arg0) {
            // TODO Auto-generated method stub
            dbl = Double.parseDouble(et1.getText().toString());
            et2.setText(dbl.toString());
        }
    });
}
}