从android中的sqlite数据库中检索数据时出现RuntimeError

Question

我正在尝试使用sqlite从eclipse中插入和检索数据库中的数据，但是它显示了RuntimeError 。 我创建了一个包含三个编辑文本和一个按钮的布局，用于从中创建简单信息，但是什么也没有创建。 我使用以下代码创建Java数据库：

package com.example.databasetest;



import android.content.ContentValues;
import android.content.Context;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;

public class DBHelper extends SQLiteOpenHelper{

    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "teacher";
    private static final String TABLE_NAME = "teacher_table";

    private static final String NAME = "teacher_name";
    private static final String FATHER_NAME = "father_name";
    private static final String MOTHER_NAME = "mother_name";

    SQLiteDatabase data=this.getWritableDatabase();

    Context ctx;



    public DBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        ctx=context;
        Log.d("DATABASE OPERATION", "DATABASE CREATED");
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        data=db;
        db.execSQL("CREATE TABLE " + TABLE_NAME + " ("
                + NAME + " TEXT,"
                + FATHER_NAME + " TEXT,"
                + MOTHER_NAME + " INTEGER,"
                + ");");
        Log.d("DATABASE OPERATION", "TABLE CREATED");


    }
     public void open() throws SQLException
     {
         DBHelper db1 = new DBHelper(ctx);
            data = db1.getWritableDatabase();
     }

     public void close()
     {
         data.close();
     }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXCEPTION EXISTS");
        onCreate(db);       
    }
    public void onInsert(DBHelper db,String name,String f_name, String m_name)
    {
        SQLiteDatabase sql= db.getWritableDatabase();
        ContentValues cv=new ContentValues();
        cv.put("teacher_name",name);
        cv.put("father_name", f_name);
        cv.put("mother_name", m_name);
        sql.insert(TABLE_NAME, null, cv);
        Log.d("DATABASE OPERATION", "ONE ROW INSERTED.....");
    }

}

和java文件为...

package com.example.databasetest;


import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;


public class MainActivity extends Activity {

    EditText NAME,FATHER,MOTHER,ID;
    String name,father,mother,id;
    int i=1;
    Button save;
    Context ctxx;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        NAME=(EditText)findViewById(R.id.name);
        FATHER=(EditText)findViewById(R.id.father_name);
        MOTHER=(EditText)findViewById(R.id.mother_name);
        ID=(EditText)findViewById(R.id.emp_id);


        save=(Button)findViewById(R.id.submit);
        save.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                id=ID.getText().toString();
                name=NAME.getText().toString();
                father=FATHER.getText().toString();
                mother=MOTHER.getText().toString();

                if(id.equals(i))
                {
                    Toast.makeText(getBaseContext(), "not allow insertion", Toast.LENGTH_LONG).show();
                }
                else
                {
                DBHelper DB=new DBHelper(ctxx);
                DB.open();
                DB.onInsert(DB, name, father, mother);
                Toast.makeText(getBaseContext(), "insertion sucessful", Toast.LENGTH_LONG).show();
                finish();
                }
            }
        });


    }
}

当我单击日志猫中的按钮时，它及其显示运行时错误..

05-08 02:54:05.932: D/AndroidRuntime(922): Shutting down VM
05-08 02:54:05.999: W/dalvikvm(922): threadid=1: thread exiting with uncaught exception (group=0x41465700)
05-08 02:54:06.189: E/AndroidRuntime(922): FATAL EXCEPTION: main
05-08 02:54:06.189: E/AndroidRuntime(922): java.lang.NullPointerException
05-08 02:54:06.189: E/AndroidRuntime(922):  at android.database.sqlite.SQLiteOpenHelper.getDatabaseLocked(SQLiteOpenHelper.java:224)
05-08 02:54:06.189: E/AndroidRuntime(922):  at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:164)
05-08 02:54:06.189: E/AndroidRuntime(922):  at com.example.databasetest.DBHelper.<init>(DBHelper.java:22)
05-08 02:54:06.189: E/AndroidRuntime(922):  at com.example.databasetest.MainActivity$1.onClick(MainActivity.java:49)
05-08 02:54:06.189: E/AndroidRuntime(922):  at android.view.View.performClick(View.java:4240)
05-08 02:54:06.189: E/AndroidRuntime(922):  at android.view.View$PerformClick.run(View.java:17721)
05-08 02:54:06.189: E/AndroidRuntime(922):  at android.os.Handler.handleCallback(Handler.java:730)
05-08 02:54:06.189: E/AndroidRuntime(922):  at android.os.Handler.dispatchMessage(Handler.java:92)
05-08 02:54:06.189: E/AndroidRuntime(922):  at android.os.Looper.loop(Looper.java:137)
05-08 02:54:06.189: E/AndroidRuntime(922):  at android.app.ActivityThread.main(ActivityThread.java:5103)
05-08 02:54:06.189: E/AndroidRuntime(922):  at java.lang.reflect.Method.invokeNative(Native Method)
05-08 02:54:06.189: E/AndroidRuntime(922):  at java.lang.reflect.Method.invoke(Method.java:525)
05-08 02:54:06.189: E/AndroidRuntime(922):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
05-08 02:54:06.189: E/AndroidRuntime(922):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
05-08 02:54:06.189: E/AndroidRuntime(922):  at dalvik.system.NativeStart.main(Native Method)
05-08 02:54:09.589: I/Process(922): Sending signal. PID: 922 SIG: 9

Answer 1

ctxx不会被初始化，这可能是崩溃的原因。 一般来说，当您处理Activity和Fragment子类时，几乎不需要保留对Context的引用。 活动的一个子类Context ，通常this是不够的。 在Fragment中，您可以使用getActivity()检索托管Fragment的Activity的上下文

CHANTE

 DBHelper DB=new DBHelper(ctxx);

同

DBHelper DB=new DBHelper(MainActivity.this);

正如@DerGolem所指出的，您正在将INTEGER类型用于MOTHER_NAME列。 可能您想使用TEXT ，并且还需要一个主键"_id"

  db.execSQL("CREATE TABLE " + TABLE_NAME + " ("
                + BaseColumns._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "
                + NAME + " TEXT,"
                + FATHER_NAME + " TEXT,"
                + MOTHER_NAME + " TEXT"
                + ");");

Answer 2

在您的活动中，在onCreate中初始化ctxx：

ctxx =此;

要么

DBHelper DB = new DBHelper（MainActivity.this）;

每当初始化数据库对象将为null时，都会得到sqlite锁定的异常。

Answer 3

也解决这个

public void onCreate(SQLiteDatabase db) {
        data=db;
        db.execSQL("CREATE TABLE " + TABLE_NAME + " ("
                + NAME + " TEXT,"
                + FATHER_NAME + " TEXT,"
                + MOTHER_NAME + " TEXT"
                + ");");
        Log.d("DATABASE OPERATION", "TABLE CREATED");


    }

对于"INTEGER,"删除.。

并像这个DBHelper一样初始化它。

DBHelper DB=new DBHelper(MainActivity.this);

Answer 4

您需要在onCreate（）方法中使用init ctxx：

ctxx = this;

如果您想进一步了解android上的sqlite->确定。 但是，如果您想减少代码量，可以尝试一些SqliteLibrary for android。 （例如ActiveAndroid，GreenDAO .....）。