在Android中处理RadioGroup和Button事件

Question

I am a beginner in Android and I am trying to create a simple Android app which has two Text boxes (EditText) to take two Numbers as Input. Then I am Creating Radio Group having four Radio Buttons (Add,Sub,Multiply,Divide). Then I am having a Button to get the results. I am getting an AlertBox saying "Unfortunately, SimpleApp has stopped working" the moment I click the Button. Kindly assist me.

* Here is my Java code *

package com.example.simpleapp;


import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.TextView;


public class MainActivity extends Activity implements OnClickListener {

    private EditText txt1; 
    private EditText txt2; 

    private String input1;
    private String input2;

    private Double Num1;
    private Double Num2;
    private String flag;
    private EditText TextResult;

    Double Result=0.0;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);
        initControls();
    }

    private void initControls()
    {

        ((Button)findViewById(R.id.button1)).setOnClickListener(this);
    }


    public void onradioButtonClicked(View view)
    {
        boolean checked = ((RadioButton) view).isChecked();


        switch(view.getId())
        {
        case R.id.radio0:
            if(checked)

                flag = "add";
                //Result = Num1+Num2;
                break;

        case R.id.radio1:
            if(checked)

                flag = "sub";
                //Result = Num1-Num2;
                break;

        case R.id.radio2:
            if(checked)

                flag = "prod";
                //Result = Num1*Num2;
                break;

        case R.id.radio3:
            if(checked)

                flag = "div";
                //Result = Num1/Num2;
                break;

        }

    }


    @Override
    public void onClick(View v) {
        // TODO Auto-generated method stub
        TextResult = (EditText)findViewById(R.id.textView2);
        TextResult.setText("0");

        txt1 = (EditText)findViewById(R.id.editText1);
        txt2 = (EditText)findViewById(R.id.editText2);

        input1 = txt1.getText().toString();
        input2 = txt2.getText().toString();

        Num1 = Double.parseDouble(input1);
        Num2 = Double.parseDouble(input2);


        if(flag == "add")
            Result = Num1+Num2;

        else if(flag == "sub")
            Result = Num1-Num2;

        else if(flag == "prod")
            Result = Num1*Num2;

        else Result = Num1/Num2;


        TextResult.setText(String.valueOf(Result));
    }

}

Here is my Activity_Main.xml

    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <LinearLayout
        android:id="@+id/linearLayout1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="102dp"
        android:layout_marginTop="66dp"
        android:orientation="vertical" >
    </LinearLayout>

    <TableRow
        android:id="@+id/tableRow1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/textView1"
        android:layout_below="@+id/linearLayout1"
        android:layout_marginTop="34dp" >
    </TableRow>

    <TableRow
        android:id="@+id/tableRow2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/tableRow1"
        android:layout_below="@+id/tableRow1"
        android:layout_marginLeft="14dp" >
    </TableRow>

    <EditText
        android:id="@+id/editText2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/tableRow1"
        android:layout_alignTop="@+id/tableRow2"
        android:ems="10"
        android:hint="Enter Second Number"
        android:inputType="number" />

    <EditText
        android:id="@+id/editText1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/linearLayout1"
        android:layout_centerHorizontal="true"
        android:ems="10"
        android:hint="Enter First Number"
        android:inputType="number" />

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/editText1"
        android:layout_alignParentTop="true"
        android:layout_marginTop="14dp"
        android:text="Simple Calculator App"
        android:textAppearance="?android:attr/textAppearanceLarge" />

    <TableRow
        android:id="@+id/tableRow3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/editText2"
        android:layout_below="@+id/editText2"
        android:layout_marginTop="36dp" >
    </TableRow>

    <RadioGroup
        android:id="@+id/radioGroup1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/textView2"
        android:layout_below="@+id/editText2" >

        <RadioButton
            android:id="@+id/radio0"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:checked="true"

            android:text="Add" 
            android:onClick="onradioButtonClicked"/>

        <RadioButton
            android:id="@+id/radio1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"

            android:text="Sub" 
            android:onClick="onradioButtonClicked"/>

        <RadioButton
            android:id="@+id/radio2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"

            android:text="Multiply"
             android:onClick="onradioButtonClicked"/>

        <RadioButton
            android:id="@+id/radio3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"

            android:text="Divide" 
            android:onClick="onradioButtonClicked"/>
    </RadioGroup>

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/linearLayout1"
        android:layout_below="@+id/radioGroup1"
        android:text="Check" 

       />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/button1"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="18dp"
        android:text=""
        android:textAppearance="?android:attr/textAppearanceLarge" />

</RelativeLayout>

Answer 1

You are Typecasted TextView into EditText.

So Android rises ClassCastException

08-03 17:08:30.415: E/AndroidRuntime(7702): java.lang.ClassCastException: android.widget.TextView

private EditText TextResult;

TextResult = (EditText)findViewById(R.id.textView2);

Change these lines into

private TextView TextResult;

TextResult = (TextView) findViewById(R.id.textView2);

Answer 2

Your if then statements have wrong syntax. Try this:

if(flag == "add"){
    Result = Num1+Num2;
}else if(flag == "sub"){
    Result = Num1-Num2;
}else if(flag == "prod"){
    Result = Num1*Num2;
}else{
    Result = Num1/Num2;
}

Answer 3

try this ... calculation on click as well as on radio button checked change

public class MainActivity  extends Activity implements OnClickListener,
    OnCheckedChangeListener {

private EditText txt1;
private EditText txt2;

// private String input1;
// private String input2;

private Double Num1;
private Double Num2;
// private String flag;
private TextView TextResult;

Double Result = 0.0;
RadioButton radio0, radio1, radio2, radio3;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.test);
    findViewById(R.id.button1).setOnClickListener(this);
    radio0 = (RadioButton) findViewById(R.id.radio0);
    radio0.setOnCheckedChangeListener(this);
    radio1 = (RadioButton) findViewById(R.id.radio1);
    radio1.setOnCheckedChangeListener(this);
    radio2 = (RadioButton) findViewById(R.id.radio2);
    radio2.setOnCheckedChangeListener(this);
    radio3 = (RadioButton) findViewById(R.id.radio3);
    radio3.setOnCheckedChangeListener(this);
    TextResult = (TextView) findViewById(R.id.textView2);
    TextResult.setText("0");

    txt1 = (EditText) findViewById(R.id.editText1);
    txt2 = (EditText) findViewById(R.id.editText2);

}

public void onradioButtonClicked(View view) {
}

@Override
public void onClick(View v) {
    getCalculationValue();
    // input1 = txt1.getText().toString();
    // input2 = txt2.getText().toString();

}

@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
    getCalculationValue();
}

private void getCalculationValue() {

    Num1 = Double.parseDouble(txt1.getText().toString().trim());
    Num2 = Double.parseDouble(txt2.getText().toString().trim());
    if (radio0.isChecked())
        Result = Num1 + Num2;
    else if (radio1.isChecked())
        Result = Num1 - Num2;
    else if (radio2.isChecked())
        Result = Num1 * Num2;
    else if (radio3.isChecked())
        Result = Num1 / Num2;
    TextResult.setText(String.valueOf(Result));
}

}