android - R cannot be resolved to a variable

Question

I would like to fix this error

R cannot be resolved to a variable

I looked up many answers, but I could not get the right one; I tried everything. Could any one help me?

My main activity which is automatically created. The error is showing for the three lines starting at case R.id.button1::

package de.vogella.android.temprature1;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.Toast;

public class Convert extends Activity {
    private EditText text;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        text = (EditText) findViewById(R.id.editText1);
    }

    // This method is called at button click because we assigned the name to the
    // "On Click property" of the button
    public void myClickHandler(View view) {
    switch (view.getId()) {
        case R.id.button1:
            RadioButton celsiusButton = (RadioButton) findViewById(R.id.radio0);
            RadioButton fahrenheitButton = (RadioButton) findViewById(R.id.radio1);
            if (text.getText().length() == 0) {
                Toast.makeText(this, "Please enter a valid number",
                Toast.LENGTH_LONG).show();
                return;
            }

            float inputValue = Float.parseFloat(text.getText().toString());
            if (celsiusButton.isChecked()) {
                text.setText(String.valueOf(convertFahrenheitToCelsius(inputValue)));
            } else {
                text.setText(String.valueOf(convertCelsiusToFahrenheit(inputValue)));
            }

            // Switch to the other button
            if (fahrenheitButton.isChecked()) {
                fahrenheitButton.setChecked(false);
                celsiusButton.setChecked(true);
            } else {
                fahrenheitButton.setChecked(true);
                celsiusButton.setChecked(false);
            }
            break;
        }
    }

    // Converts to celsius
    private float convertFahrenheitToCelsius(float fahrenheit) {
        return ((fahrenheit - 32) * 5 / 9);
    }

    // Converts to fahrenheit
    private float convertCelsiusToFahrenheit(float celsius) {
        return ((celsius * 9) / 5) + 32;
    }
}

my main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="fill_parent"
    android:layout_height="fill_parent" android:background="@color/myColor">
    <EditText android:layout_height="wrap_content" android:id="@+id/editText1"
        android:layout_width="match_parent" android:inputType="numberDecimal|numberSigned"></EditText>
    <RadioGroup android:layout_height="wrap_content" android:id="@+id/radioGroup1"
        android:layout_width="match_parent">
        <RadioButton android:layout_width="wrap_content"
            android:id="@+id/radio0" android:layout_height="wrap_content"
            android:text="@string/celsius" android:checked="true"></RadioButton>
        <RadioButton android:layout_width="wrap_content"
            android:id="@+id/radio1" android:layout_height="wrap_content"
            android:text="@string/fahrenheit"></RadioButton>
    </RadioGroup>
    <Button android:id="@+id/button1" android:layout_width="wrap_content"
        android:layout_height="wrap_content" android:text="@string/calc"
        android:onClick="myClickHandler"></Button>
</LinearLayout>

my string.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="hello">Hello World, Convert!</string>
    <string name="app_name">de.vogella.android.temprature1</string>
<string name="myClickHandler">myClickHandler</string>
<string name="celsius">to Celsius</string>
<string name="farenheit">to Farenheit</string>
<string name="calc">Calculate</string>
</resources>

Answer 1

1) see if the xml files in the Package Explorer tree have an error-icon if they do, fix errors and R-class will be generated.

example hint: FILL_PARENT was renamed MATCH_PARENT in API Level 8; so if you're targeting platform 2.1 (api 7), change all occurences back to "fill_parent"

2) if you added "import android.R;" trying to do a quick-fix, remove that line