如何將課堂上的練習從課堂傳遞給另一課程？

Question

在下面給出的代碼，我需要從SQLlite的數據庫中逐個刪除聯繫人數據。
爲此，我寫在數據庫Handler.java類的方法。
但主要AndroidSQLiteTutorialActivity.java類使用此方法時我在傳遞參數。問題（我在哪裏寫的評論：「我覺得這裏的問題」）。

我怎麼可以跟蹤數據庫中的所有聯繫人保存檢查它存在與否。如果數據庫中存在聯繫人（數據），我需要在屏幕上顯示彈出按鈕？

這就是Android AndroidSQLiteTutorialActivity.java類

package com.androidhive.androidsqlite; 

import java.util.List; 

import android.app.Activity; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.Button; 
import android.widget.EditText; 


public class AndroidSQLiteTutorialActivity extends Activity { 
/** Called when the activity is first created. */ 
@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    final EditText editText = (EditText)findViewById(R.id.editText2); 
    final EditText editText2 = (EditText)findViewById(R.id.editText3); 
    Button button = (Button)findViewById(R.id.button1); 
    button.setOnClickListener(new OnClickListener() { 

    @Override 
    public void onClick(View arg0) { 
     // TODO Auto-generated method stub 
     String str1 = editText.getText().toString(); 
     String str2 = editText2.getText().toString(); 




    DatabaseHandler db = new DatabaseHandler(AndroidSQLiteTutorialActivity.this); 


    /** 
    * CRUD Operations 
    * */ 
    // Inserting Contacts 
    Log.d("Insert: ", "Inserting .."); 
    // db.addContact(new Contact(str1, str2)); 
    //db.addContact(new Contact(str2, "9199999999")); 
    //db.addContact(new Contact("Tommy", "9522222222")); 
    //db.addContact(new Contact("Karthik", "9533333333")); 

    // Reading all contacts 

    db.deleteContact("What should i need to pass here"???) //Here I feel problem 

    Log.d("Reading: ", "Reading all contacts.."); 
    List<Contact> contacts = db.getAllContacts();  

    for (Contact cn : contacts) { 
     String log = "Id: "+cn.getID()+" ,Name: " + cn.getName() + " ,Phone: " + cn.getPhoneNumber(); 
      // Writing Contacts to log 
    Log.d("Name: ", log); 

    } 

    } 
    }); 


    } 
} 

這是一個DatabaseHandler.java類

package com.androidhive.androidsqlite; 

import java.util.ArrayList; 
import java.util.List; 

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

public class DatabaseHandler extends SQLiteOpenHelper { 

// All Static variables 
// Database Version 
private static final int DATABASE_VERSION = 1; 

// Database Name 
private static final String DATABASE_NAME = "contactsManager"; 

// Contacts table name 
private static final String TABLE_CONTACTS = "contacts"; 

// Contacts Table Columns names 
private static final String KEY_ID = "id"; 
private static final String KEY_NAME = "name"; 
private static final String KEY_PH_NO = "phone_number"; 

public DatabaseHandler(Context context) { 
    super(context, DATABASE_NAME, null, DATABASE_VERSION); 
} 

// Creating Tables 
@Override 
public void onCreate(SQLiteDatabase db) { 
    String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "(" 
      + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT," 
      + KEY_PH_NO + " TEXT" + ")"; 
    db.execSQL(CREATE_CONTACTS_TABLE); 
} 

// Upgrading database 
@Override 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
    // Drop older table if existed 
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS); 

    // Create tables again 
    onCreate(db); 
} 

/** 
* All CRUD(Create, Read, Update, Delete) Operations 
*/ 

// Adding new contact 
void addContact(Contact contact) { 
    SQLiteDatabase db = this.getWritableDatabase(); 

    ContentValues values = new ContentValues(); 
    values.put(KEY_NAME, contact.getName()); // Contact Name 
    values.put(KEY_PH_NO, contact.getPhoneNumber()); // Contact Phone 

    // Inserting Row 
    db.insert(TABLE_CONTACTS, null, values); 
    db.close(); // Closing database connection 
} 

// Getting single contact 
Contact getContact(int id) { 
    SQLiteDatabase db = this.getReadableDatabase(); 

    Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID, 
      KEY_NAME, KEY_PH_NO }, KEY_ID + "=?", 
      new String[] { String.valueOf(id) }, null, null, null, null); 
    if (cursor != null) 
     cursor.moveToFirst(); 

    Contact contact = new Contact(Integer.parseInt(cursor.getString(0)), 
      cursor.getString(1), cursor.getString(2)); 
    // return contact 
    return contact; 
} 

// Getting All Contacts 
public List<Contact> getAllContacts() { 
    List<Contact> contactList = new ArrayList<Contact>(); 
    // Select All Query 
    String selectQuery = "SELECT * FROM " + TABLE_CONTACTS; 

    SQLiteDatabase db = this.getWritableDatabase(); 
    Cursor cursor = db.rawQuery(selectQuery, null); 

    // looping through all rows and adding to list 
    if (cursor.moveToFirst()) { 
     do { 
      Contact contact = new Contact(); 
      contact.setID(Integer.parseInt(cursor.getString(0))); 
      contact.setName(cursor.getString(1)); 
      contact.setPhoneNumber(cursor.getString(2)); 
      // Adding contact to list 
      contactList.add(contact); 
     } while (cursor.moveToNext()); 
    } 

    // return contact list 
    return contactList; 
} 

// Updating single contact 
public int updateContact(Contact contact) { 
    SQLiteDatabase db = this.getWritableDatabase(); 

    ContentValues values = new ContentValues(); 
    values.put(KEY_NAME, contact.getName()); 
    values.put(KEY_PH_NO, contact.getPhoneNumber()); 

    // updating row 
    return db.update(TABLE_CONTACTS, values, KEY_ID + " = ?", 
      new String[] { String.valueOf(contact.getID()) }); 
} 

// Deleting single contact 
public void deleteContact(Contact contact) { 
    SQLiteDatabase db = this.getWritableDatabase(); 
    db.delete(TABLE_CONTACTS, KEY_ID + " = ?", 
      new String[] { String.valueOf(contact.getID()) }); 
    db.close(); 
} 


// Getting contacts Count 
public int getContactsCount() { 
    String countQuery = "SELECT * FROM " + TABLE_CONTACTS; 
    SQLiteDatabase db = this.getReadableDatabase(); 
    Cursor cursor = db.rawQuery(countQuery, null); 
    cursor.close(); 

    // return count 
    return cursor.getCount(); 
} 

} 

Answer 1

看看你自己的文檔，你應該通過一個聯繫對象檢查this鏈接（我假設您複製並沒有真正理解你在做什麼的代碼 - 爲一個忠告，你真的不能由在做違背學習複製學習..），看看你的數據庫內容使用源碼的Eclipse插件讀者或導入數據庫到您的計算機使用this app或退房this SO線程或this指南