在SQLite Android中创建数据库并将值插入表中

Question

我在做什么：:我正在尝试创建数据库并将值插入其中的表

我面临的问题：：未创建我的数据库（我在DDMS中检查了）

MainActivity.java

public class MainActivity extends Activity implements OnClickListener {

        Button addUser;
        EditText name,pwd;
        DatabaseAdapter adapter;
        Context context;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            addUser=(Button) findViewById(R.id.button1);
            name=(EditText) findViewById(R.id.editText1);
            pwd=(EditText) findViewById(R.id.editText2);
        }

        @Override
        protected void onStart() {
            // TODO Auto-generated method stub
            super.onStart();
            addUser.setOnClickListener(this);
        }


        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub

            switch(v.getId()){
            case R.id.button1:

                long returnedRes = 0;
                try {
                    returnedRes = adapter.insertData(name.getText().toString(), pwd.getText().toString());
                } catch (Exception e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    Log.d("Log-EXCEPTION", e.toString());
                }


                if(returnedRes<0)
                {
                    Message.message(this, "Unsuccessful");
                    Log.d("LOG-MSG", "Unsuccessful");
                }else{
                    Message.message(this, "Successful");
                    Log.d("LOG-MSG", "Successful");
                }
                break;
            }
        }
}

DatabaseAdapter.java

public class DatabaseAdapter {

    DatabaseHelper helper;
    ContentValues cv;
    SQLiteDatabase db;

    //Constructor of outer class
    DatabaseAdapter(Context context){
        helper=new DatabaseHelper(context);//creating object of Inner class
    }

    public long insertData(String name,String password){
        db=helper.getWritableDatabase();
        cv.put(helper.NAME, name);
        cv.put(helper.PASSWORD, password);
        long id=db.insert(helper.TABLE_NAME, null, cv); 
        /*
         * -1 if the value is inserted has some problem 
         * else it will return the rowId of the column inserted
        */
        return id;
    }

    class DatabaseHelper extends SQLiteOpenHelper{

        private Context context;
        private static final String DATABASE_NAME="MyDatabase";
        private static final String TABLE_NAME="MyTable";
        private static final int DATABASE_VERSION=1;

        private static final String ID="_id";
        private static final String NAME="name";
        private static final String PASSWORD="password";


        private static final String CREATE_TABLE="CREATE TABLE "+TABLE_NAME+"("+ID+" INT PRIMARY KEY AUTO_INCREMENT, "+NAME+" VARCHAR(225), "+PASSWORD+" VARCHAR(225));";
        private static final String DROP_TABLE="DROP TABLE IF EXISTS "+TABLE_NAME+"";

        public DatabaseHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
            this.context=context;
            Message.message(context, "Constructor \n called");
            Log.d("LOG-MSG", "Constructor \n called");
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            //CREATE TABLE MyTable(_id INT PRIMARY KEY AUTO_INCREMENT, name VARCHAR(225));
            try {
                Message.message(context, "onCreate \n called");
                Log.d("LOG-MSG", "onCreate \n called");
                db.execSQL(CREATE_TABLE);
            } catch (SQLException e) {
                Message.message(context, ""+e);
            }
        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            //DROP TABLE MyTable IF EXISTS;
            try {
                Message.message(context, "onUpgrade \n called");
                Log.d("LOG-MSG", "onUpgrade \n called");
                db.execSQL(DROP_TABLE);
                onCreate(db);
            } catch (SQLException e) {
                Message.message(context, ""+e);
            }
        }

    }


}

日志 ::

04-18 09:47:51.250: W/ActivityThread(6470): Application com.example.sqliteslidenerdproject is waiting for the debugger on port 8100...
04-18 09:47:51.350: I/System.out(6470): Sending WAIT chunk
04-18 09:47:51.600: I/dalvikvm(6470): Debugger is active
04-18 09:47:51.790: I/System.out(6470): Debugger has connected
04-18 09:47:51.790: I/System.out(6470): waiting for debugger to settle...
04-18 09:47:51.990: I/System.out(6470): waiting for debugger to settle...
04-18 09:47:52.191: I/System.out(6470): waiting for debugger to settle...
04-18 09:47:52.390: I/System.out(6470): waiting for debugger to settle...
04-18 09:47:52.600: I/System.out(6470): waiting for debugger to settle...
04-18 09:47:52.800: I/System.out(6470): waiting for debugger to settle...
04-18 09:47:53.002: I/System.out(6470): waiting for debugger to settle...
04-18 09:47:53.202: I/System.out(6470): waiting for debugger to settle...
04-18 09:47:53.410: I/System.out(6470): waiting for debugger to settle...
04-18 09:47:53.610: I/System.out(6470): waiting for debugger to settle...
04-18 09:47:53.820: I/System.out(6470): waiting for debugger to settle...
04-18 09:47:54.020: I/System.out(6470): waiting for debugger to settle...
04-18 09:47:54.220: I/System.out(6470): waiting for debugger to settle...
04-18 09:47:54.420: I/System.out(6470): waiting for debugger to settle...
04-18 09:47:54.630: I/System.out(6470): waiting for debugger to settle...
04-18 09:47:54.830: I/System.out(6470): debugger has settled (1427)
04-18 09:48:06.050: D/gralloc_goldfish(6470): Emulator without GPU emulation detected.
04-18 09:48:28.411: W/System.err(6470): java.lang.NullPointerException
04-18 09:48:28.441: W/System.err(6470):     at com.example.sqliteslidenerdproject.MainActivity.onClick(MainActivity.java:47)
04-18 09:48:28.600: W/System.err(6470):     at android.view.View.performClick(View.java:3480)
04-18 09:48:28.633: W/System.err(6470):     at android.view.View$PerformClick.run(View.java:13983)
04-18 09:48:28.650: W/System.err(6470):     at android.os.Handler.handleCallback(Handler.java:605)
04-18 09:48:28.661: W/System.err(6470):     at android.os.Handler.dispatchMessage(Handler.java:92)
04-18 09:48:28.681: W/System.err(6470):     at android.os.Looper.loop(Looper.java:137)
04-18 09:48:28.702: W/System.err(6470):     at android.app.ActivityThread.main(ActivityThread.java:4340)
04-18 09:48:28.721: W/System.err(6470):     at java.lang.reflect.Method.invokeNative(Native Method)
04-18 09:48:28.741: W/System.err(6470):     at java.lang.reflect.Method.invoke(Method.java:511)
04-18 09:48:28.761: W/System.err(6470):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
04-18 09:48:28.791: W/System.err(6470):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
04-18 09:48:28.801: W/System.err(6470):     at dalvik.system.NativeStart.main(Native Method)
04-18 09:48:28.821: D/Log-EXCEPTION(6470): java.lang.NullPointerException
04-18 09:48:32.651: D/LOG-MSG(6470): Successful

Answer 1

我认为您忘记了如下初始化的DatabaseAdapter adapter ：

DatabaseAdapter adapter=new DatabaseAdapter(MainActivity.this);

您的应用程序崩溃是因为适配器在您使用Button Click事件上的adapter.insertData(.....)处为null 。

更新：您在“ Create Table SQL command也犯了错误

"CREATE TABLE "+TABLE_NAME+"("+ID+" INT PRIMARY KEY AUTO_INCREMENT // Remove _ from AUTO_INCREMENT from after primary key and also change INT to INTEGER

使用以下更正您的Create Table SQL command

    private static final String CREATE_TABLE="CREATE TABLE "+TABLE_NAME+"("+ID+" INTEGER PRIMARY KEY AUTOINCREMENT, "+NAME+" VARCHAR(225), "+PASSWORD+" VARCHAR(225));";

Answer 2

我认为您忘记了初始化adapter变量。 这就是为什么您会收到NULL POINTER Exception原因。请尝试对其进行初始化，然后再次运行。

在onCreate（）中添加此行

adapter   = new DatabaseAdapter(MainActivity.this);

Answer 3

我认为适配器为空，因为您尚未创建类DatabaseAdapter的实例

尝试下面的代码。

 try {

   adapter = new DatabaseAdapter(MainActivity.this);

   returnedRes = adapter.insertData(name.getText().toString(), pwd.getText().toString());
} catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        Log.d("Log-EXCEPTION", e.toString());
 }