得到了RunTimeException异常

Question

我的LogCat报出异常：

java.lang.RunTimeException: Unable to instantiate activity ComponentInfo{com.erikbalen.idealgaslawcalculator/com.erikbalen.idealgaslawcalculator.NumberActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity{ActivityThread.java:2121}

java文件如下：

public class NumberActivity extends Activity {    
EditText pressure = (EditText) findViewById(R.id.editTextPressure);
EditText temperature = (EditText) findViewById(R.id.editTextTemperature);
EditText volume = (EditText) findViewById(R.id.editTextVolume);
TextView answer = (TextView) findViewById(R.id.textViewSolve);
Button solve = (Button) findViewById(R.id.buttonSolve);    
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_number);
    solve.setOnClickListener(new View.OnClickListener() {    
        @Override
        public void onClick(View v) {
            double pressureValue = Double.parseDouble(pressure.getText().toString());
            double temperatureValue = Double.parseDouble(temperature.getText().toString());
            double volumeValue = Double.parseDouble(volume.getText().toString());
            double r = 0.0821;
            double answerValue = (pressureValue*volumeValue)/(r*temperatureValue);
            answer.setText(Double.toString(answerValue));
        }
    });
}
}

请高手帮忙，谢谢。

Answer 1

findViewById(R.id.editTextPressure)赋值操作放在 setContentView(R.layout.activity_number);后面