我在android中实现了一个数据库，当我尝试将用户插入数据库时，我会看到一个Null Poiner异常。我调试了用户输入的详细信息，那里有信息。
这是我的DbManager.java类
package com.fyp.run_race;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
public class DbManager
{
public static final String KEY_USER_ID = "_id";
public static final String KEY_USER_EMAIL = "email";
public static final String KEY_USER_WEIGHT = "weight";
public static final String KEY_USER_HEIGHT = "height";
public static final String KEY_TRACK_ID = "_id";
public static final String KEY_TRACK_FILEPATH = "file_path";
public static final String KEY_TRACK_NAME = "track_name";
public static final String KEY_TRACK_LOCATION = "location";
public static final String KEY_TRACK_TYPE = "track_type";
public static final String KEY_TRACK_CALORIES = "calories";
public static final String KEY_TRACK_DISTANCE = "distance";
public static final String KEY_TRACK_MAX_SPEED = "max_speed";
public static final String KEY_TRACK_AVG_SPEED = "avg_speed";
static final String USER_TABLE = "USERINFO";
static final String TRACK_TABLE = "TRACK";
private Context context;
private DbHelper dbHelper;
private SQLiteDatabase db;
public DbManager(Context cnxt)
{
this.context = cnxt;
}
public DbManager open() throws SQLException
{
dbHelper = new DbHelper(context);
db = dbHelper.getReadableDatabase();
return this;
}
public void close()
{
dbHelper.close();
}
public long createUser(String email, float weight, float height)
{
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_USER_EMAIL, email);
initialValues.put(KEY_USER_WEIGHT, weight);
initialValues.put(KEY_USER_HEIGHT, height);
return db.insert(USER_TABLE, null, initialValues);
}
public long createTrack(String filePath,String trackName, String location, String trackType, float calories, float distance, float avgSpeed, float maxSpeed)
{
ContentValues initialValues = new ContentValues();
initialValues.put(KEY_TRACK_FILEPATH, filePath);
initialValues.put(KEY_TRACK_NAME, trackName);
initialValues.put(KEY_TRACK_LOCATION, location);
initialValues.put(KEY_TRACK_TYPE, trackType);
initialValues.put(KEY_TRACK_CALORIES, calories);
initialValues.put(KEY_TRACK_DISTANCE, distance);
initialValues.put(KEY_TRACK_AVG_SPEED, avgSpeed);
initialValues.put(KEY_TRACK_MAX_SPEED, maxSpeed);
return db.insert(TRACK_TABLE, null, initialValues);
}
public boolean deleteUser(long rowId)
{
return db.delete(USER_TABLE, KEY_USER_ID+"="+rowId, null) > 0 ;
}
public boolean deleteTrack(long rowId)
{
return db.delete(TRACK_TABLE, KEY_TRACK_ID+"="+rowId, null) > 0 ;
}
public Cursor getAllUsers()
{
return db.query(true, USER_TABLE, new String[]{KEY_USER_ID,KEY_USER_EMAIL,KEY_USER_WEIGHT,KEY_USER_HEIGHT }, null, null, null, null, null, null);
}
public Cursor getAllTracks()
{
return db.query(true, TRACK_TABLE, new String[]{KEY_TRACK_ID,KEY_TRACK_FILEPATH,KEY_TRACK_NAME,KEY_TRACK_LOCATION,KEY_TRACK_TYPE, KEY_TRACK_CALORIES, KEY_TRACK_DISTANCE, KEY_TRACK_AVG_SPEED,KEY_TRACK_MAX_SPEED}, null, null, null, null, null, null);
}
public Cursor getUser(long rowId)
{
Cursor myCursor = db.query(true, USER_TABLE, new String[]{KEY_USER_ID,KEY_USER_EMAIL,KEY_USER_WEIGHT,KEY_USER_HEIGHT }, KEY_USER_ID + "="+ rowId, null, null, null, null, null);
if(myCursor != null)
{
myCursor.moveToFirst();
}
return myCursor;
}
public Cursor getTrack(long rowId)
{
Cursor myCursor = db.query(true, TRACK_TABLE, new String[]{KEY_TRACK_ID,KEY_TRACK_FILEPATH,KEY_TRACK_NAME,KEY_TRACK_LOCATION,KEY_TRACK_TYPE, KEY_TRACK_CALORIES, KEY_TRACK_DISTANCE, KEY_TRACK_AVG_SPEED,KEY_TRACK_MAX_SPEED}, KEY_TRACK_ID+ "=" + rowId, null,
null, null, null, null);
if(myCursor != null)
{
myCursor.moveToFirst();
}
return myCursor;
}
public boolean updateUser(long rowId,String email, float weight, float height)
{
ContentValues args = new ContentValues();
args.put(KEY_USER_EMAIL, email);
args.put(KEY_USER_WEIGHT, weight);
args.put(KEY_USER_HEIGHT, height);
return db.update(USER_TABLE, args, KEY_USER_ID + "=" + rowId, null) > 0;
}
}
logcat正在标识db manager类
中的第59行return db.insert(USER_TABLE, null, initialValues);
和Enter_User_Details.java类中的第66行long id = db.createUser(vEmail, Float.parseFloat(vWeight), Float.parseFloat(vHeight));
这是完整的Enter_User_Details类
package com.fyp.run_race;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.text.Editable;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import com.fyp.run_race.DbManager;
public class Enter_User_Details extends Activity
{
private DbManager db;
Long rowId = null;
EditText email,weight,height;
Button confirm,clear;
String vEmail, vWeight,vHeight;
boolean emailCheck;
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.user_details);
db = new DbManager(this);
email = (EditText)findViewById(R.id.EmailEntry);
weight = (EditText)findViewById(R.id.Weight);
height = (EditText)findViewById(R.id.Height);
confirm = (Button)findViewById(R.id.ConfirmBtn);
clear = (Button)findViewById(R.id.ClearBtn);
confirm.setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View arg0)
{
// TODO Auto-generated method stub
vEmail = email.getText().toString();
vWeight = weight.getText().toString();
vHeight = height.getText().toString();
if(vEmail.equalsIgnoreCase("")||vWeight.equalsIgnoreCase("")||vHeight.equalsIgnoreCase(""))
{
Toast.makeText(Enter_User_Details.this, "All fields are required", Toast.LENGTH_LONG).show();
}
if(isNumeric(vWeight) == true && isNumeric(vHeight) == true)
{
Toast.makeText(Enter_User_Details.this, "Weight or Height must be a number", Toast.LENGTH_LONG).show();
}
checkEmail(vEmail);
if(emailCheck == true)
{
System.out.println("Email: "+vEmail+" Weight: "+Float.parseFloat(vWeight)+" Height: "+Float.parseFloat(vHeight));
long id = db.createUser(vEmail, Float.parseFloat(vWeight), Float.parseFloat(vHeight));
db.close();
Intent i = new Intent(Enter_User_Details.this, Begin_Run.class);
startActivity(i);
}
}
});
}
public static boolean isNumeric(String str)
{
try
{
float f = Float.parseFloat(str);
}
catch(NumberFormatException nfe)
{
return false;
}
return true;
}
private void checkEmail(String vEmail)
{
// TODO Auto-generated method stub
Pattern pattern = Pattern.compile(".+@.+\\.[a-z]+");
Matcher matcher = pattern.matcher(vEmail);
emailCheck = matcher.matches();
}
}
这里是Logcat输出包含System.out.println以显示用户输入的文件实际上有数据
02-12 14:36:29.802: I/System.out(1693): Email: sean.w.hannon@gmail.com Weight: 75.5 Height: 160.5
02-12 14:36:29.802: D/AndroidRuntime(1693): Shutting down VM
02-12 14:36:29.802: W/dalvikvm(1693): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
02-12 14:36:29.812: E/AndroidRuntime(1693): FATAL EXCEPTION: main
02-12 14:36:29.812: E/AndroidRuntime(1693): java.lang.NullPointerException
02-12 14:36:29.812: E/AndroidRuntime(1693): at com.fyp.run_race.DbManager.createUser(DbManager.java:59)
02-12 14:36:29.812: E/AndroidRuntime(1693): at com.fyp.run_race.Enter_User_Details$1.onClick(Enter_User_Details.java:66)
02-12 14:36:29.812: E/AndroidRuntime(1693): at android.view.View.performClick(View.java:2408)
02-12 14:36:29.812: E/AndroidRuntime(1693): at android.view.View$PerformClick.run(View.java:8816)
02-12 14:36:29.812: E/AndroidRuntime(1693): at android.os.Handler.handleCallback(Handler.java:587)
02-12 14:36:29.812: E/AndroidRuntime(1693): at android.os.Handler.dispatchMessage(Handler.java:92)
02-12 14:36:29.812: E/AndroidRuntime(1693): at android.os.Looper.loop(Looper.java:123)
02-12 14:36:29.812: E/AndroidRuntime(1693): at android.app.ActivityThread.main(ActivityThread.java:4627)
02-12 14:36:29.812: E/AndroidRuntime(1693): at java.lang.reflect.Method.invokeNative(Native Method)
02-12 14:36:29.812: E/AndroidRuntime(1693): at java.lang.reflect.Method.invoke(Method.java:521)
02-12 14:36:29.812: E/AndroidRuntime(1693): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
02-12 14:36:29.812: E/AndroidRuntime(1693): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
02-12 14:36:29.812: E/AndroidRuntime(1693): at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：1)
我认为DbHelper dbHelper是null，因为您从不致电DbManager.open()！
尝试在db.open()中db.createUser(..)之前添加Enter_User_Details。