在我的Android应用程序中，我也使用了checkbox，单选按钮和微调器。但在启动此应用程序时，它显示致命错误。 我的java代码如下：
package com.example.exam;
import android.os.Bundle;
import android.app.Activity;
import android.app.AlertDialog.Builder;
import android.content.Context;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.DatePicker;
import android.widget.DatePicker.OnDateChangedListener;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.Spinner;
import android.widget.TextView;
public class MainActivity extends Activity implements OnItemSelectedListener, OnClickListener {
private TextView t_fname;
private EditText e_fname;
private EditText e_lname;
private TextView t_lname;
private TextView t_email;
private EditText e_email;
private TextView t_pw;
private EditText e_pw;
private EditText e_dob;
private TextView t_dob;
private TextView t_gender;
private RadioButton r_male;
private TextView t_hobbies;
private RadioButton r_female;
private CheckBox ch1;
private CheckBox ch3;
private CheckBox ch2;
private CheckBox ch4;
private CheckBox ch5;
private CheckBox ch6;
private TextView t_country;
private EditText e_country;
private DatePicker datePicker1;
private Button b1;
String[] place=new String[]{"India","australia","france","japan","USA","UK"};
private Spinner spin;
SQLiteDatabase db;
private String gender="";
private String hobbies="";
private String country="";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//database
db=openOrCreateDatabase("Registration", Context.MODE_PRIVATE, null);
db.execSQL("CREATE TABLE IF NOT EXISTS Student(firstname VARCHAR,lastname VARCHAR," +
"email VARCHAR,password VARCHAR,dob VARCHAR,gender VARCHAR,hobbies VARCHAR,country VARCHAR );");
//notation
t_fname=(TextView)findViewById(R.id.t_fname);
e_fname=(EditText)findViewById(R.id.e_fname);
t_lname=(TextView)findViewById(R.id.t_lname);
e_lname=(EditText)findViewById(R.id.e_lname);
t_email=(TextView)findViewById(R.id.t_email);
e_email=(EditText)findViewById(R.id.e_email);
t_pw=(TextView)findViewById(R.id.t_pw);
e_pw=(EditText)findViewById(R.id.e_pw);
t_dob=(TextView)findViewById(R.id.t_dob);
e_dob=(EditText)findViewById(R.id.e_dob);
t_gender=(TextView)findViewById(R.id.t_gender);
r_male=(RadioButton)findViewById(R.id.r_male);
r_female=(RadioButton)findViewById(R.id.r_female);
t_hobbies=(TextView)findViewById(R.id.t_hobbies);
ch1=(CheckBox)findViewById(R.id.ch1);
ch2=(CheckBox)findViewById(R.id.ch2);
ch3=(CheckBox)findViewById(R.id.ch3);
ch4=(CheckBox)findViewById(R.id.ch4);
ch5=(CheckBox)findViewById(R.id.ch5);
ch6=(CheckBox)findViewById(R.id.ch6);
t_country=(TextView)findViewById(R.id.t_country);
b1 = (Button)findViewById(R.id.b1);
datePicker1 = (DatePicker) findViewById(R.id.datePicker1);
b1.setOnClickListener(this);
//spinner portion//
Spinner spin=(Spinner)findViewById(R.id.spin);
spin.setOnItemSelectedListener(this);
ArrayAdapter aa=new ArrayAdapter(this,android.R.layout.simple_spinner_item,place );
aa.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spin.setAdapter(aa);
//date picker
class MyOnDateChangedListener implements OnDateChangedListener{
@Override
public void onDateChanged(DatePicker view, int year, int monthOfYear,
int dayOfMonth) {
// TODO Auto-generated method stub
e_dob.setText( "" + dayOfMonth + "-" + (monthOfYear + 1) + "-" + year );
}
};
}
//checkbox portion//
private void CheckBoxClicked(View view) {
// TODO Auto-generated method stub
// Check that the button is now checked?
boolean checked = ((CheckBox) view).isChecked();
// Check which radio button was clicked
switch(view.getId()) {
case R.id.ch1:
if (checked)
hobbies = "Music";
break;
case R.id.ch2:
if (checked)
hobbies = "Travel";
break;
case R.id.ch3:
if (checked)
hobbies = "Dance";
break;
case R.id.ch4:
if (checked)
hobbies = "Cooking";
break;
case R.id.ch5:
if (checked)
hobbies = "Reading";
break;
case R.id.ch6:
if (checked)
hobbies = "Surfing";
break;
}
db.execSQL("INSER INTO Registrartion VALUES('"+hobbies+"');");
}
//radio button
public void RadioButtonClicked(View view) {
//This variable will store whether the user was male or female
// Check that the button is now checked?
boolean checked = ((RadioButton) view).isChecked();
// Check which radio button was clicked
switch(view.getId()) {
case R.id.r_female:
if (checked)
gender = "female";
break;
case R.id.r_male:
if (checked)
gender = "male";
break;
}
db.execSQL("INSERT INTO Registrartion VALUES('"+gender+"');");
}
@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 void onItemSelected(AdapterView<?> arg0, View arg1, int Position,
long id) {
// TODO Auto-generated method stub
country = spin.getSelectedItem().toString();
db.execSQL("INSERT INTO Registrartion VALUES('"+country+"');");
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
// TODO Auto-generated method stub
showMessage("empty tag","plz fill the detail");
}
private void showMessage(String title, String message) {
// TODO Auto-generated method stub
Builder builder=new Builder(this);
builder.setCancelable(true);
builder.setTitle(title);
builder.setMessage(message);
builder.show();
}
@Override
public void onClick(View view) {
// TODO Auto-generated method stub
if(view==b1){
if(e_fname.getText().toString().trim().length()==0 ||
e_lname.getText().toString().trim().length()==0||
e_email.getText().toString().trim().length()==0 ||
e_pw.getText().toString().trim().length()==0||
e_dob.getText().toString().trim().length()==0 ||
gender == null|| hobbies ==null || country ==null)
{
showMessage("Error","Please enter all the fields.");
return;
}
db.execSQL("INSERT INTO Student VALUES('"+e_fname.getText()+"','"+e_lname.getText()+"','"+e_email.getText()+"','"+e_pw.getText()+"','"+e_dob.getText()+"','"+gender+"','"+hobbies+"','"+country+"');");
showMessage("Success", "Successfully registered");
clearText();
Intent i=new Intent(getApplicationContext(),Next.class);
startActivity(i);
}
}
private void clearText() {
// TODO Auto-generated method stub
e_fname.setText("");
e_lname.setText("");
e_email.setText("");
e_pw.setText("");
e_dob.setText("");
e_fname.requestFocus();
}
}
启动此应用程序时，它已停止。
答案 0 :(得分：0)
这不是空指针异常的原因（堆栈跟踪对此有帮助），但是在您发布的代码中还有一些其他错误。在onCreate中，您有以下代码：
db=openOrCreateDatabase("Registration", Context.MODE_PRIVATE, null);
db.execSQL("CREATE TABLE IF NOT EXISTS Student(firstname VARCHAR,lastname VARCHAR," +
"email VARCHAR,password VARCHAR,dob VARCHAR,gender VARCHAR,hobbies VARCHAR,country VARCHAR );");
在onItemSelected（）调用中，您有以下语句：
db.execSQL("INSERT INTO Registrartion VALUES('"+country+"');");
以及代码中其他地方的类似陈述。我认为这些破坏的INSERTS是出于某种目的的占位符，因为你的代码在onClick（）中包含一个有效的INSERT语句，但点击任何这些行将导致你的代码因缺少表而失败，或者在一种情况下因为你说INSER而不是INSERT。
至于其余部分，如果没有你的布局文件，我可以检查其他一些内容（但是你的数据库打开和表创建不会导致问题）。