Android App Datenbank Löschen Funktion funktioniert nicht, aber Funktion Hinzufügen funktioniert

Question

Ich bin ein Anfänger für Android App, und lernen Sie es von Bucky Tutorial. Für die Datenbank, ich denke, ich habe den gleichen Code mit dem Tutorial online, aber Add-Funktion funktioniert perfekt, aber die Funktion Löschen funktioniert nicht.

Fehler:

03-25 03:32:16.401 2212-2212/com.thenewboston.sqlite I/art: Not late-enabling -Xcheck:jni (already on) 
03-25 03:32:16.578 2212-2212/com.thenewboston.sqlite W/System: ClassLoader referenced unknown path: /data/app/com.thenewboston.sqlite-1/lib/x86 
03-25 03:32:17.216 2212-2238/com.thenewboston.sqlite D/OpenGLRenderer: Use EGL_SWAP_BEHAVIOR_PRESERVED: true 
03-25 03:32:17.849 2212-2238/com.thenewboston.sqlite I/OpenGLRenderer: Initialized EGL, version 1.4 
03-25 03:32:17.997 2212-2238/com.thenewboston.sqlite W/EGL_emulation: eglSurfaceAttrib not implemented 
03-25 03:32:17.997 2212-2238/com.thenewboston.sqlite W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0xabf311e0, error=EGL_SUCCESS 
03-25 03:32:18.271 2212-2212/com.thenewboston.sqlite I/Choreographer: Skipped 59 frames! The application may be doing too much work on its main thread. 
03-25 03:32:18.998 2212-2212/com.thenewboston.sqlite I/Choreographer: Skipped 42 frames! The application may be doing too much work on its main thread. 
03-25 03:32:33.633 2212-2212/com.thenewboston.sqlite W/IInputConnectionWrapper: getSelectedText on inactive InputConnection 
03-25 03:32:33.648 2212-2212/com.thenewboston.sqlite W/IInputConnectionWrapper: getSelectedText on inactive InputConnection 
03-25 03:32:33.648 2212-2212/com.thenewboston.sqlite W/IInputConnectionWrapper: requestCursorAnchorInfo on inactive InputConnection 
03-25 03:32:33.649 2212-2212/com.thenewboston.sqlite W/IInputConnectionWrapper: getTextBeforeCursor on inactive InputConnection 
03-25 03:32:33.650 2212-2212/com.thenewboston.sqlite W/IInputConnectionWrapper: getTextBeforeCursor on inactive InputConnection 
03-25 03:32:33.651 2212-2212/com.thenewboston.sqlite W/IInputConnectionWrapper: getTextBeforeCursor on inactive InputConnection 
03-25 03:32:40.513 2212-2223/com.thenewboston.sqlite W/art: Suspending all threads took: 92.247ms 

MainActivity:

package com.thenewboston.sqlite; 

import android.os.Bundle; 
import android.support.design.widget.FloatingActionButton; 
import android.support.design.widget.Snackbar; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.Toolbar; 
import android.view.View; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.widget.EditText; 
import android.widget.TextView; 
import android.os.Handler; 
import android.os.Message; 

public class MainActivity extends AppCompatActivity { 

    EditText willsInput; 
    TextView willsText; 
    MyDBHandler dbHandler; 
    Handler handler = new Handler(){ 
     @Override 
     public void handleMessage(Message msg) { 
      printDatabase(); 
     } 
    }; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     willsInput = (EditText) findViewById(R.id.input); 
     willsText = (TextView)findViewById(R.id.WillsText); 
     dbHandler = new MyDBHandler(this, null, null, 1); 
     printDatabase(); 
    } 

    //Add a product to the database 
    public void addButtonClicked(View view){ 
     Runnable r = new Runnable() { 
      @Override 
      public void run() { 
       Products product = new Products(willsInput.getText().toString()); 
       dbHandler.addProduct(product); 
       handler.sendEmptyMessage(0); 
      } 
     }; 
     Thread willsThread = new Thread(r); 
     willsThread.start(); 
    } 

    //Delete products 
    public void deleteButtonClicked(View view){ 
     Runnable a = new Runnable() { 
      @Override 
      public void run() { 
       String inputText = willsText.getText().toString(); 
       dbHandler.deleteProduct(inputText); 
       handler.sendEmptyMessage(0); 
      } 
     }; 
     Thread threada = new Thread(a); 
     threada.start(); 

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


} 

Produkte Klasse:

package com.thenewboston.sqlite; 

public class Products { 

    private int _id; 
    private String _productname; 

    public Products(){ 

    } 

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

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

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

    public int get_id() { 
     return _id; 
    } 

    public String get_productname() { 
     return _productname; 
    } 
} 

MyDBHandler:

package com.thenewboston.sqlite; 

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 = 1; 
    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 a 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 a product from database 
    public void deleteProduct(String productName){ 
     SQLiteDatabase db = getWritableDatabase(); 
     db.execSQL("DELETE FROM " + TABLE_PRODUCTS + " WHERE " + COLUMN_PRODUCTNAME + "=\"" + productName + "\";"); 
    } 

    //Print out the database as a String 
    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 you results 
     c.moveToFirst(); 

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

      } 
      c.moveToNext(); 
     } 
     db.close(); 
     return dbString; 
    } 
} 

Jemand bitte helfen Sie mir. Ich weiß wirklich nicht, wo der Bug ist. Danke! AddButtonClicked funktioniert einwandfrei. Das einzige Problem ist deleteButtonClicked

Danke nochmal.

Answer 1

Verwenden Sie "\" nicht für "="

FALSCH = db.execSQL ("DELETE FROM" + TABLE_PRODUCTS + "WHERE" + COLUMN_PRODUCTNAME + "= \" "+ product +" \ ";");

KORREKT = db.execSQL ("DELETE FROM" + TABELLE_PRODUKTE + "WHERE" + COLUMN_PRODUCTNAME + "=" + productName);

oder

db.delete ("TABLE_PRODUCTS", COLUMN_PRODUCTNAME + "=" + Product-null);