小编Kev*_*vsy的帖子

我在执行以下代码时在第41行(setText)上收到java.lang.NullPointerException错误.

我之前看到过使用此行设置的EditText框,我不明白我做错了什么.

我没有使用eclipse或java的经验,但我正在努力学习.请帮忙!

码:

package Psychrometric.Calculator;

import android.app.Activity;
import android.app.AlertDialog;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.text.TextUtils;
import android.os.Bundle;

public class Calculator extends Activity {

private EditText altitude;
private EditText barometricPressure;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
           setContentView(R.layout.main);

    Button calcButton = (Button) findViewById(R.id.calcButton);

    calcButton.setOnClickListener(new OnClickListener() {
            public void onClick(View arg0) {        

            altitude = (EditText) findViewById(R.id.altitude);


            if (altitude.getText().length() != 0) 
            {

                double altitudeDouble = …