等于计算器不执行任何操作的按钮（Android Developer Tools）

Question

I cant really figure out, I am beginner to programming, doing it for about 2 months. I have made calculator for Android, but problem is that equals button does nothing.

Setting up different variables:

Button one,two,three,four,five,six,seven,eight,nine,zero,plus,minus,divide,multiply,dot,equals;
ImageButton clear;
TextView result;
String theresult;

All buttons except equals just append respective text to variable result.

Here is code of only equal button(created just plus to test, but failed):

    equals = (Button) findViewById(R.id.equals);
    equals.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            String expression = String.valueOf(result);

            if(expression.contains("+")){
            String[] numbers = expression.split("\\+");
            String no1 = numbers[0];
            String no2 = numbers[1];

            Double numb1 = Double.valueOf(no1);
            Double numb2 = Double.valueOf(no2);
            Double added = numb1+numb2;

            theresult = String.valueOf(added);
            result.setText(theresult);


            }
        }
    });

I have used if here, so that I can use else if to make other operations work. Later on I will use Try-Catch block too. Thank you for your time!

Full code of MainActivity.java

package org.example.calc;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.TextView;

public class MainActivity extends Activity {

Button one,two,three,four,five,six,seven,eight,nine,zero,plus,minus,divide,multiply,dot,equals;
ImageButton clear;
TextView result;
String theresult;




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

    result = (TextView) findViewById(R.id.result);

    one = (Button) findViewById(R.id.one);
    one.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            result.append("1");
        }
    });


    two = (Button) findViewById(R.id.two);
    two.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            result.append("2");
        }
    });

    three = (Button) findViewById(R.id.three);
    three.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            result.append("3");
        }
    });

    four = (Button) findViewById(R.id.four);
    four.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            result.append("4");
        }
    });

    five = (Button) findViewById(R.id.five);
    five.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            result.append("5");
        }
    });


    six = (Button) findViewById(R.id.six);
    six.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            result.append("6");
        }
    });


    seven = (Button) findViewById(R.id.seven);
    seven.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            result.append("7");
        }
    });

    eight = (Button) findViewById(R.id.eight);
    eight.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            result.append("8");
        }
    });

    nine = (Button) findViewById(R.id.nine);
    nine.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            result.append("9");
        }
    });


    zero = (Button) findViewById(R.id.zero);
    zero.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            result.append("0");
        }
    });

    dot = (Button) findViewById(R.id.dot);
    dot.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            result.append(".");
        }
    });


    clear = (ImageButton) findViewById(R.id.clear);
    clear.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            result.setText("");
        }
    });


    plus = (Button) findViewById(R.id.plus);
    plus.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            result.append("+");
        }
    });

    minus = (Button) findViewById(R.id.minus);
    minus.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            result.append("-");
        }
    });

    divide = (Button) findViewById(R.id.divide);
    divide.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            result.append("/");
        }
    });


    multiply = (Button) findViewById(R.id.multiply);
    multiply.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            result.append("x");
        }
    });


    equals = (Button) findViewById(R.id.equals);
    equals.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            result.getText();
            String expression = String.valueOf(result);

            if(expression.contains("+")){
            String[] numbers = expression.split("\\+");
            String no1 = numbers[0];
            String no2 = numbers[1];

            Double numb1 = Double.valueOf(no1);
            Double numb2 = Double.valueOf(no2);
            Double added = numb1+numb2;

            theresult = String.valueOf(added);
            result.setText(theresult);


            }
        }
    });




}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

}

Answer 1

Just do thus:

@Override
public void onClick(View v) {
    String expression = result.getText().toString();
    // Log.d("LOG", expression);

    if(expression.contains("+")){
        (...)

Maybe work. No need of using String.valueOf()

Answer 2

When you press your equals button you have to get the value of the textview by result.getText() so that you will get the value of text view and assign it in some string. String expression = String.valueOf(result);

Here you are simply using the result in String.valueOf(). Check whether your are getting the correct value or not by debugging or some sort of print statments.

Also post your code completely/reasonable code to avoid more questions so that you will get your answer.