SQLiteDatabase中的java.lang.NullPointerException错误Android

请你能帮我解决“java.lang.NullPointerException”这个错误。我试图将一些数据（名称和电子邮件）保存在数据库中，然后加载它。当我尝试启动它时，我的应用程序在模拟器中崩溃。我寻找答案，碰到这个线程： Error java.lang.NullPointerException on method getReadableDatabase()但它并没有解决这个问题。SQLiteDatabase中的java.lang.NullPointerException错误Android

MainActivity.java

package com.example.test; 

import android.support.v7.app.ActionBarActivity; 
import android.support.v7.app.ActionBar; 
import android.support.v4.app.Fragment; 
import android.database.Cursor; 
import android.os.Bundle; 
import android.view.LayoutInflater; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.MotionEvent; 
import android.view.View; 
import android.view.View.OnTouchListener; 
import android.view.ViewGroup; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.Toast; 
import android.os.Build; 

public class MainActivity extends ActionBarActivity { 
Button save, load; 
EditText name, email; 
DataHandler handler; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    save = (Button)findViewById(R.id.save); 
    load = (Button)findViewById(R.id.load); 
    name = (EditText)findViewById(R.id.name); 
    email = (EditText)findViewById(R.id.email); 

    save.setOnTouchListener(new OnTouchListener(){ 
     public void onClick(View v){ 

     } 

     @Override 
     public boolean onTouch(View v, MotionEvent event) { 
      // TODO Auto-generated method stub 
      String getName = name.getText().toString(); 
      String getEmail = email.getText().toString(); 
      handler = new DataHandler(getBaseContext()); 
      handler.open(); 
      long id = handler.insertData(getName, getEmail); 
      Toast.makeText(getBaseContext(), "Data inserted", Toast.LENGTH_LONG).show(); 
      handler.close(); 
      return false; 
     } 
    }); 

    load.setOnTouchListener(new OnTouchListener(){ 

     @Override 
     public boolean onTouch(View v, MotionEvent event) { 
      // TODO Auto-generated method stub 
      String getName, getEmail; 
      getName = ""; 
      getEmail = ""; 
      handler = new DataHandler(getBaseContext()); 
      handler.open(); 
      Cursor C = handler.returnData(); 
      if(C.moveToFirst()) 
      { 
       do 
       { 
        getName = C.getString(0); 
        getEmail = C.getString(1); 
       }while(C.moveToNext()); 
      } 
      handler.close(); 
      Toast.makeText(getBaseContext(), "Name : "+getName+" and email : "+getEmail, Toast.LENGTH_LONG).show(); 
      return false; 
     } 

    }); 

    if (savedInstanceState == null) { 
     getSupportFragmentManager().beginTransaction() 
       .add(R.id.container, new PlaceholderFragment()) 
       .commit(); 
    } 
} 


@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 boolean onOptionsItemSelected(MenuItem item) { 
    // Handle action bar item clicks here. The action bar will 
    // automatically handle clicks on the Home/Up button, so long 
    // as you specify a parent activity in AndroidManifest.xml. 
    int id = item.getItemId(); 
    if (id == R.id.action_settings) { 
     return true; 
    } 
    return super.onOptionsItemSelected(item); 
} 

/** 
* A placeholder fragment containing a simple view. 
*/ 
public static class PlaceholderFragment extends Fragment { 

    public PlaceholderFragment() { 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
      Bundle savedInstanceState) { 
     View rootView = inflater.inflate(R.layout.fragment_main, container, false); 
     return rootView; 
    } 
} 

}

DataHandler.java

package com.example.test; 

import android.content.ContentValues; 
import android.content.Context; 
import android.database.Cursor; 
import android.database.SQLException; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteDatabase.CursorFactory; 
import android.database.sqlite.SQLiteOpenHelper; 

public class DataHandler { 
public static final String NAME = "name"; 
public static final String EMAIL = "email"; 
public static final String TABLE_NAME = "mytable"; 
public static final String DATA_BASE_NAME = "mydatabase"; 
public static final int DATABASE_VERSION = 1; 
public static final String TABLE_CREATE = "create table mytable (name text not null, email text not null);"; 

DataBaseHelper dbhelper; 
private static Context ctx; 
SQLiteDatabase db; 
public DataHandler(Context ctx) 
{ 
    this.ctx = ctx; 
    dbhelper = new DataBaseHelper(ctx); 
} 

private static class DataBaseHelper extends SQLiteOpenHelper 
{ 
    public DataBaseHelper(Context ctx) 
    { 
     super(ctx, DATA_BASE_NAME, null, DATABASE_VERSION); 
    } 

    @Override 
    public void onCreate(SQLiteDatabase db) 
    { 
     try{ 
     db.execSQL("TABLE_CREATE"); 
     } 
     catch(SQLException e) 
     { 
      e.printStackTrace(); 
     } 
    } 

    @Override 
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
    { 
     db.execSQL("DROP TABLE IF EXISTS mytable"); 
     onCreate(db); 

    } 

} 

public DataHandler open() 
{ 
    db = dbhelper.getWritableDatabase(); 
    return this; 
} 

public void close() 
{ 
    dbhelper.close(); 
} 

public long insertData(String name, String email) 
{ 
    ContentValues content = new ContentValues(); 
    content.put(NAME, name); 
    content.put(EMAIL, email); 
    return db.insertOrThrow(TABLE_NAME, null, content); 
} 

public Cursor returnData() 
{ 
    return db.query(TABLE_NAME, new String[] {NAME, EMAIL}, null, null, null, null, null); 
} 
}

activity_main.xml中

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
xmlns:tools="http://schemas.android.com/tools" 
android:id="@+id/container" 
android:layout_width="match_parent" 
android:layout_height="match_parent" 
android:paddingBottom="@dimen/activity_vertical_margin" 
android:paddingLeft="@dimen/activity_horizontal_margin" 
android:paddingRight="@dimen/activity_horizontal_margin" 
android:paddingTop="@dimen/activity_vertical_margin" 
tools:context="com.example.test.MainActivity" 
tools:ignore="MergeRootFrame" > 

<EditText 
    android:id="@+id/name" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_below="@+id/textView1" 
    android:layout_centerHorizontal="true" 
    android:layout_marginTop="36dp" 
    android:ems="10" 
    android:hint="Enter name here" > 

    <requestFocus /> 
</EditText> 

<Button 
    android:id="@+id/load" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignParentBottom="true" 
    android:layout_alignRight="@+id/save" 
    android:layout_marginBottom="81dp" 
    android:text="LOAD DATA" /> 

<EditText 
    android:id="@+id/email" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_alignLeft="@+id/name" 
    android:layout_below="@+id/name" 
    android:layout_marginTop="41dp" 
    android:ems="10" 
    android:hint="Enter email here" /> 

<Button 
    android:id="@+id/save" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:layout_above="@+id/load" 
    android:layout_centerHorizontal="true" 
    android:layout_marginBottom="42dp" 
    android:text="SAVE DATA" /> 

</RelativeLayout>

logcat的

05-11 14:09:06.363: E/AndroidRuntime(2259): FATAL EXCEPTION: main 
05-11 14:09:06.363: E/AndroidRuntime(2259): Process: com.example.test, PID: 2259 
05-11 14:09:06.363: E/AndroidRuntime(2259): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test/com.example.test.MainActivity}: java.lang.NullPointerException 
05-11 14:09:06.363: E/AndroidRuntime(2259):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195) 
05-11 14:09:06.363: E/AndroidRuntime(2259):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245) 
05-11 14:09:06.363: E/AndroidRuntime(2259):  at android.app.ActivityThread.access$800(ActivityThread.java:135) 
05-11 14:09:06.363: E/AndroidRuntime(2259):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196) 
05-11 14:09:06.363: E/AndroidRuntime(2259):  at android.os.Handler.dispatchMessage(Handler.java:102) 
05-11 14:09:06.363: E/AndroidRuntime(2259):  at android.os.Looper.loop(Looper.java:136) 
05-11 14:09:06.363: E/AndroidRuntime(2259):  at android.app.ActivityThread.main(ActivityThread.java:5017) 
05-11 14:09:06.363: E/AndroidRuntime(2259):  at java.lang.reflect.Method.invokeNative(Native Method) 
05-11 14:09:06.363: E/AndroidRuntime(2259):  at java.lang.reflect.Method.invoke(Method.java:515) 
05-11 14:09:06.363: E/AndroidRuntime(2259):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
05-11 14:09:06.363: E/AndroidRuntime(2259):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
05-11 14:09:06.363: E/AndroidRuntime(2259):  at dalvik.system.NativeStart.main(Native Method) 
05-11 14:09:06.363: E/AndroidRuntime(2259): Caused by: java.lang.NullPointerException 
05-11 14:09:06.363: E/AndroidRuntime(2259):  at com.example.test.MainActivity.onCreate(MainActivity.java:34) 
05-11 14:09:06.363: E/AndroidRuntime(2259):  at android.app.Activity.performCreate(Activity.java:5231) 
05-11 14:09:06.363: E/AndroidRuntime(2259):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087) 
05-11 14:09:06.363: E/AndroidRuntime(2259):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159) 
05-11 14:09:06.363: E/AndroidRuntime(2259):  ... 11 more

转贴DataHandler.java编辑后

package com.example.test; 

import android.content.ContentValues; 
import android.content.Context; 
import android.database.Cursor; 
import android.database.SQLException; 
import android.database.sqlite.SQLiteDatabase; 
import android.database.sqlite.SQLiteDatabase.CursorFactory; 
import android.database.sqlite.SQLiteOpenHelper; 

public class DataHandler { 
public static final String NAME = "name"; 
public static final String EMAIL = "email"; 
public static final String TABLE_NAME = "mytable"; 
public static final String DATA_BASE_NAME = "mydatabase"; 
public static final int DATABASE_VERSION = 1; 
public static final String TABLE_CREATE = "create table mytable (name text not null, email text not null)"; 

DataBaseHelper dbhelper; 
Context ctx; 
SQLiteDatabase db; 
public DataHandler(Context ctx) 
{ 
    this.ctx = ctx; 
    dbhelper = new DataBaseHelper(ctx); 
} 

private static class DataBaseHelper extends SQLiteOpenHelper 
{ 
    public DataBaseHelper(Context ctx) 
    { 
     super(ctx, DATA_BASE_NAME, null, DATABASE_VERSION); 
    } 

    @Override 
    public void onCreate(SQLiteDatabase db) 
    { 
     try{ 
     db.execSQL(TABLE_CREATE); 
     } 
     catch(SQLException e) 
     { 
      e.printStackTrace(); 
     } 
    } 

    @Override 
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
    { 
     db.execSQL("DROP TABLE IF EXISTS mytable"); 
     onCreate(db); 

    } 

} 

public DataHandler open() 
{ 
    db = dbhelper.getWritableDatabase(); 
    return this; 
} 

public void close() 
{ 
    dbhelper.close(); 
} 

public long insertData(String name, String email) 
{ 
    ContentValues content = new ContentValues(); 
    content.put(NAME, name); 
    content.put(EMAIL, email); 
    return db.insertOrThrow(TABLE_NAME, null, content); 
} 

public Cursor returnData() 
{ 
    return db.query(TABLE_NAME, new String[] {NAME, EMAIL}, null, null, null, null, null); 
} 
}

来源

2014-05-12 rde

我想这是'支架在onCreate（）方法的'} missplace – Kedarnath

检查是否'activity_main'布局包含“保存”按钮。也可以在'OnTouchListener'中使用'return true;'。最后，从'save.setOnTouchListener'中删除'public void onClick（View v）{ }'' – SathishKumar

@SathishKumar这有助于启动应用程序。但只要输入姓名和电子邮件并点击保存，它就会崩溃。在LogCat上它说 05-12 00：19：47.393：E/AndroidRuntime（3048）：android.database.sqlite.SQLiteException：没有这样的表：mytable（代码1）：编译时：INSERT INTO mytable（email，name ）VALUES（？，？） – rde

所有的事情，你已经做了正确的，但错过了onCreate()DataHandler.java内的一件小事。

@Override 
     public void onCreate(SQLiteDatabase db) 
     { 
      try{ 
      //db.execSQL("TABLE_CREATE"); 
      // Here you passing `TABLE_CREATE` string instead of passing `TABLE_CREATE` variable's string. So kindly remove quotes surrounded by 'TABLE_CREATE' and try. 
       db.execSQL(TABLE_CREATE); 
      } 
      catch(SQLException e) 
      { 
       e.printStackTrace(); 
      } 
     }

而改变这一状况，

public static final String TABLE_CREATE = "create table mytable (name text not null, email text not null);";

到

public static final String TABLE_CREATE = "create table mytable (name text not null, email text not null)";

来源

2014-05-12 04:35:36 SathishKumar

这仍然给出相同的错误。 – rde

在'TABLE_CREATE'结尾删除';' – SathishKumar

我删除了;在TABLE_CREATE查询的最后，我得到了同样的错误：05-12 00：51：48.673：E/AndroidRuntime（3225）：android.database.sqlite.SQLiteException：no such table：mytable（code 1）：，当编译时：INSERT INTO mytable（email，name）VALUES（？，？） – rde

它似乎并不涉及到SQLite的一个问题。

您发布的痕迹说，错误是发生在第34行：

save.setOnTouchListener(new OnTouchListener(){

所以你save按钮必须当你尝试应用事件为空。

检查线29实际上返回你和实例：

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

来源

2014-05-12 03:30:08 BonanzaOne

谢谢。我不确定我了解你的建议。 – rde

@rde从您发布的代码中，我确实认为在第34行尝试应用该事件时，保存按钮为空。我所建议的是，确保保存按钮不为空时，当您应用事件，因为跟踪是建议它，并且按钮是dinamically引用的。 – BonanzaOne

实际上，我的activity_main.xml出现问题，这就是为什么保存按钮变为空。我编辑它。 – rde

请使用此..

save.setOnTouchListener(new View.OnTouchListener() { 

    @Override 
    public boolean onTouch(View v, MotionEvent event) { 
     String getName = name.getText().toString(); 
     String getEmail = email.getText().toString(); 
     handler = new DataHandler(getBaseContext()); 
     handler.open(); 
     long id = handler.insertData(getName, getEmail); 
     Toast.makeText(getBaseContext(), "Data inserted", Toast.LENGTH_LONG).show(); 
     handler.close(); 
     return false; 
      } 
     });

我觉得你ontouch（）似乎problem.please把我的代码，而不是你的代码..它可能是工作..

来源

2014-05-12 03:45:35 dipali

谢谢。但它似乎没有帮助。我仍然得到同样的错误。 – rde

哪一行你得到错误？ – dipali

SQLiteDatabase中的java.lang.NullPointerException错误Android

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