当我在android studio模拟器

Question

我尝试从EditText获取输入，点击button后，它会将数据保存在数据库中并显示在textview中。但是当我运行我的应用程序时，它会持续显示以下错误并显示白屏。

11-04 08:25:25.360    1925-1925/com.example.usaukglu.databaselearning I/art﹕ Not late-enabling -Xcheck:jni (already on)
11-04 08:25:26.329    1925-1937/com.example.usaukglu.databaselearning I/art﹕ WaitForGcToComplete blocked for 16.058ms for cause Background
11-04 08:25:26.875    1925-1937/com.example.usaukglu.databaselearning I/art﹕ Background sticky concurrent mark sweep GC freed 10318(8MB) AllocSpace objects, 0(0B) LOS objects, 0% free, 13MB/13MB, paused 60.083ms total 502.110ms
11-04 08:25:27.009    1925-1937/com.example.usaukglu.databaselearning W/art﹕ Suspending all threads took: 19.606ms


package com.example.usaukglu.databaselearning;

import android.app.Activity;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;


public class MainActivity extends Activity {
EditText editText;
Button button;
TextView textView;
MyDbHandler myDbHandler;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    editText = (EditText) findViewById(R.id.editText);
    button = (Button) findViewById(R.id.button);
    textView = (TextView) findViewById(R.id.textView);

   myDbHandler=new MyDbHandler(this,null,null,1);
   //printDatabase();
}
public void addButtonClicked(View view){
    Product product =new Product(editText.getText().toString());
    myDbHandler.addProduct(product);
  printDatabase();
}
public void printDatabase() {
    String dbString=myDbHandler.databaseToString();
    textView.setText(dbString);
     editText.setText("");

}
}



package com.example.usaukglu.databaselearning;

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


public class MyDbHandler extends SQLiteOpenHelper {
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "product.db";
private static final String TABLE_NAME = "product";
private static final String COLUMN_ID = "_id";
private static final String COLUMN_PRODUCTNAME = "productName";


public MyDbHandler(Context context, String name,SQLiteDatabase.CursorFactory   factory, int version)      {
    super(context, DATABASE_NAME, factory, DATABASE_VERSION);
}

@Override
public void onCreate(SQLiteDatabase sqLiteDatabase) {

    String query = "CREATE TABLE " + TABLE_NAME
            + "(" + COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
            + COLUMN_PRODUCTNAME  +" TEXT);";
    sqLiteDatabase.execSQL(query);
}

@Override
public void onUpgrade(SQLiteDatabase sqLiteDatabase, int i, int i2) {
    sqLiteDatabase.execSQL("DROP TABLE IF EXISTS" + TABLE_NAME);
    onCreate(sqLiteDatabase);

}

public void addProduct(Product product) {
    ContentValues values = new ContentValues();
    values.put(COLUMN_PRODUCTNAME, product.get_productName());
    SQLiteDatabase sqLiteDatabase = getWritableDatabase();
    sqLiteDatabase.insert(TABLE_NAME, null, values);
    sqLiteDatabase.close();
}
//Print out the database as a string
public String databaseToString() {
    String dbString = "";
    SQLiteDatabase sqLiteDatabase = getWritableDatabase();
    String query="SELECT * FROM " + TABLE_NAME + " WHERE 1";

    //Cursor point to a location in  results
    Cursor c=sqLiteDatabase.rawQuery(query,null);

    //Move to the first row in results
    c.moveToFirst();

    while (!c.isAfterLast()){
        if (c.getString(c.getColumnIndex("productName"))!=null){
            dbString+=c.getString(c.getColumnIndex("productName"));
            dbString+="\n";
        }
    }
    sqLiteDatabase.close();
    return dbString;
}

}

package com.example.usaukglu.databaselearning;


public class Product {
private int _id;
private String _productName;

public  Product(){

}

public Product(String productName){
    this._productName = productName;

}

public int get_id() {
    return _id;
}

public void set_id(int _id) {
    this._id = _id;
}

public String get_productName() {
    return _productName;
}

public void set_productName(String _productName) {
    this._productName = _productName;
}
}