Question

首先应用程序会在我使用模拟器启动它时崩溃，不知道我改变了什么让它运行但现在它将运行onCreate方法然而，当我实现addButtonClicked方法时，应用程序只是停止并且Android Monitor每隔几秒钟显示“暂停所有线程”，我不确定从哪里开始调试。任何指向正确方向的人都会非常感激，因为我对Android开发还不熟悉。

MainActivity.java

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

EditText testInput;
TextView testText;
MyDBHandler dbHandler;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    testInput = (EditText) findViewById(R.id.testInput);
    testText = (TextView) findViewById(R.id.testText);
    dbHandler = new MyDBHandler(this, null, null, 1);

    printDatabase();
}
//Add product to database

public void addButtonClicked(View view){
    Products product = new Products((testInput.getText().toString()));
    dbHandler.addProduct(product);
    printDatabase();
}

// Delete Items

public void deleteButtonClicked(View view){
    String inputText = testText.getText().toString();
    dbHandler.deleteProduct(inputText);
    printDatabase();
}


public void printDatabase(){
    String dbString = dbHandler.databaseToString();
    testText.setText(dbString);
    testInput.setText("");
}
}

Products.java

public class Products {
private int _id;
private String _productname;

public Products(){
}

public Products(String productname) {
    this._productname = productname;
}

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

public void set_productname(String _productname) {
    this._productname = _productname;
}

public int get_id() {
    return _id;
}

public String get_productname() {
    return _productname;
}

}

MyDBHandler.java

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

public class MyDBHandler extends SQLiteOpenHelper {

private static final int DATABASE_VERSION = 15;
private static final String DATABASE_NAME = "products.db";
public static final String TABLE_PRODUCTS = "products";
public static final String COLUMN_ID = "_id";
public 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 db) {
    String query = "CREATE TABLE " + TABLE_PRODUCTS +"(" +
            COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT ," +
            COLUMN_PRODUCTNAME +" TEXT " +
            ");";

    db.execSQL(query);
}

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

//Add new row to the database
public void addProduct(Products product){
    ContentValues values = new ContentValues();
    values.put(COLUMN_PRODUCTNAME, product.get_productname());
    SQLiteDatabase db = getWritableDatabase();
    db.insert(TABLE_PRODUCTS, null, values);
    db.close();
}

//Delete product from database
public void deleteProduct(String productName){
    SQLiteDatabase db = getWritableDatabase();
    db.execSQL("DELETE FROM " + TABLE_PRODUCTS + " WHERE " + COLUMN_PRODUCTNAME + "=\"" + productName + "\";" );
}

//Print of DB as sting
public String databaseToString(){
    String dbString = "";
    SQLiteDatabase db = getWritableDatabase();
    String query = "SELECT * FROM " + TABLE_PRODUCTS + " WHERE 1";

    //Cursor point to a location in your results
    Cursor c = db.rawQuery(query, null);
    //Move to the first row in your results
    c.moveToFirst();

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


}

Answer 1

您正在执行检索操作的databaseToString方法。您应该在UI线程以外的线程中执行读取操作。尝试在AsyncTask中获取。它应该工作。您的databaseToString的实现应该由AsyncTask处理。

快乐编码..

Android应用程序在实现SQLite数据库时停滞不前

1 个答案: