从SQLite数据库到其他活动的Android Studio ListView

对不起，如果这被证明是愚蠢的。我试图从一个具有3个EditText字段，标题，描述和例程的活动中获取用户的一些数据，并将其放入SQLite数据库（并且是的，我使用的是DBAdapter），然后将其显示在另一个活动列表中视图。问题是，在我填写字段并按下保存按钮调用onClick_AddTask函数，然后返回到列表视图活动后，没有明显的错误，但列表视图为空。我确实在logcat中出现了一些错误，但我无法真正理解它。任何形式的洞察力或建设性的批评总是受欢迎的，谢谢。从SQLite数据库到其他活动的Android Studio ListView

将对DBAdapter：

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

public class DBAdapter { 

private static final String TAG = "DBAdapter"; //used for logging database version changes 

// Field Names: 
public static final String KEY_ROWID = "_id"; 
public static final String KEY_TASK = "task"; 
public static final String KEY_DESCRIPTION = "description"; 
public static final String KEY_DATE = "date"; 
public static final String KEY_EXERCISES = "exercises"; 

public static final String[] ALL_KEYS = new String[] {KEY_ROWID, KEY_TASK, KEY_DESCRIPTION, KEY_DATE, KEY_EXERCISES}; 

// Column Numbers for each Field Name: 
public static final int COL_ROWID = 0; 
public static final int COL_TASK = 1; 
public static final int COL_DATE = 2; 
public static final int COL_DESCRIPTION = 3; 
public static final int COL_EXERCISES = 4; 

// DataBase info: 
public static final String DATABASE_NAME = "dbToDo"; 
public static final String DATABASE_TABLE = "mainToDo"; 
public static final int DATABASE_VERSION = 3; // The version number must be incremented each time a change to DB structure occurs. 

//SQL statement to create database 
private static final String DATABASE_CREATE_SQL = 
     "CREATE TABLE " + DATABASE_TABLE 
     + " (" + KEY_ROWID + " INTEGER PRIMARY KEY AUTOINCREMENT, " 
     + KEY_TASK + " TEXT NOT NULL, " 
     + KEY_DATE + " TEXT, " 
     + KEY_DESCRIPTION + " TEXT, " 
     + KEY_EXERCISES + " TEXT" 
     + ");"; 

private final Context context; 
private DatabaseHelper myDBHelper; 
private SQLiteDatabase db; 


public DBAdapter(Context ctx) { 
    this.context = ctx; 
    myDBHelper = new DatabaseHelper(context); 
} 

// Open the database connection. 
public DBAdapter open() { 
    db = myDBHelper.getWritableDatabase(); 
    return this; 
} 

// Close the database connection. 
public void close() { 
    myDBHelper.close(); 
} 

// Add a new set of values to be inserted into the database. 
public long insertRow(String task, String date, String description, String exercises) { 
    ContentValues initialValues = new ContentValues(); 
    initialValues.put(KEY_TASK, task); 
    initialValues.put(KEY_DATE, date); 
    initialValues.put(KEY_DESCRIPTION, description); 
    initialValues.put(KEY_EXERCISES, exercises); 


    // Insert the data into the database. 
    return db.insert(DATABASE_TABLE, null, initialValues); 
} 

// Delete a row from the database, by rowId (primary key) 
public boolean deleteRow(long rowId) { 
    String where = KEY_ROWID + "=" + rowId; 
    return db.delete(DATABASE_TABLE, where, null) != 0; 
} 

public void deleteAll() { 
    Cursor c = getAllRows(); 
    long rowId = c.getColumnIndexOrThrow(KEY_ROWID); 
    if (c.moveToFirst()) { 
     do { 
      deleteRow(c.getLong((int) rowId));    
     } while (c.moveToNext()); 
    } 
    c.close(); 
} 

// Return all data in the database. 
public Cursor getAllRows() { 
    String where = null; 
    Cursor c = db.query(true, DATABASE_TABLE, ALL_KEYS, where, null, null, null, null, null); 
    if (c != null) { 
     c.moveToFirst(); 
    } 
    return c; 
} 

// Get a specific row (by rowId) 
public Cursor getRow(long rowId) { 
    String where = KEY_ROWID + "=" + rowId; 
    Cursor c = db.query(true, DATABASE_TABLE, ALL_KEYS, 
        where, null, null, null, null, null); 
    if (c != null) { 
     c.moveToFirst(); 
    } 
    return c; 
} 

// Change an existing row to be equal to new data. 
public boolean updateRow(long rowId, String task, String date) { 
    String where = KEY_ROWID + "=" + rowId; 
    ContentValues newValues = new ContentValues(); 
    newValues.put(KEY_TASK, task); 
    newValues.put(KEY_DATE, date); 
    // Insert it into the database. 
    return db.update(DATABASE_TABLE, newValues, where, null) != 0; 
} 


private static class DatabaseHelper extends SQLiteOpenHelper 
{ 
    DatabaseHelper(Context context) { 
     super(context, DATABASE_NAME, null, DATABASE_VERSION); 
    } 

    @Override 
    public void onCreate(SQLiteDatabase _db) { 
     _db.execSQL(DATABASE_CREATE_SQL);   
    } 

    @Override 
    public void onUpgrade(SQLiteDatabase _db, int oldVersion, int newVersion) { 
     Log.w(TAG, "Upgrading application's database from version " + oldVersion 
       + " to " + newVersion + ", which will destroy all old data!"); 

     // Destroy old database: 
     _db.execSQL("DROP TABLE IF EXISTS " + DATABASE_TABLE); 

     // Recreate new database: 
     onCreate(_db); 
    } 
}

}

主要活动：

import android.content.Intent; 
import android.database.Cursor; 
import android.support.v4.widget.SimpleCursorAdapter; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.support.v7.widget.ButtonBarLayout; 
import android.text.TextUtils; 
import android.text.format.Time; 
import android.view.View; 
import android.widget.AdapterView; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.ListView; 
import android.widget.Toast; 

import java.util.List; 

public class MainActivity extends AppCompatActivity { 

Time today = new Time(Time.getCurrentTimezone()); 
DBAdapter myDB; 
EditText title; 
Button newTask; 
EditText description; 
EditText routine; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 
    title = (EditText) findViewById(R.id.editTextTask); 
    description = (EditText) findViewById(R.id.editDescriptionTask); 
    routine = (EditText) findViewById(R.id.editRoutineTask); 
    newTask = (Button) findViewById(R.id.buttonNew); 

    newTask.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      startActivity(new Intent(MainActivity.this, MenuActivity.class)); 
     } 
    }); 

    openDB(); 
    populateListView(); 
    listViewItemClick(); 
    listViewItemLongClick(); 

} 

private void openDB() { 
    myDB = new DBAdapter(this); 
    myDB.open(); 
} 

public void populateListView() { 
    Cursor cursor = myDB.getAllRows(); 

    String[] fromFieldNames = new String[] { 
      DBAdapter.KEY_ROWID,DBAdapter.KEY_TASK,DBAdapter.KEY_DESCRIPTION 
    }; 

    int[] toViewIDs = new int[] { 
      R.id.textViewItemNumber, R.id.textViewItemTask, R.id.textViewItemDescription 
    }; 

    SimpleCursorAdapter myCursorAdapter; 
    myCursorAdapter = new SimpleCursorAdapter(getBaseContext(),R.layout.item_layout,cursor,fromFieldNames,toViewIDs,0); 
    ListView myList = (ListView)findViewById(R.id.listViewTasks); 
    myList.setAdapter(myCursorAdapter); 
} 

private void updateTask(long id) { 
    Cursor cursor = myDB.getRow(id); 
    if(cursor.moveToFirst()) { 
     String task = title.getText().toString(); 
     today.setToNow(); 
     String date = today.format("%Y-%M-%D %H:%M:%S"); 
     myDB.updateRow(id, task, date); 
    } 

    cursor.close(); 
} 

private void listViewItemClick() { 
    ListView myList = (ListView) findViewById(R.id.listViewTasks); 
    myList.setOnItemClickListener(new AdapterView.OnItemClickListener() { 

     @Override 
     public void onItemClick(AdapterView<?> adapterView, View view, int arg2, long id) { 
      updateTask(id); 
      populateListView(); 
      displayToast(id); 
     } 
    }); 
} 

public void onClick_AddTask(View v) { 
    today.setToNow(); 
    String timeStamp = today.format("%Y-%M-%D %H:%M:%S"); 
    if(!TextUtils.isEmpty(title.getText().toString())) { 
     myDB.insertRow(title.getText().toString(), timeStamp, description.getText().toString(), routine.getText().toString()); 
    } 
    populateListView(); 
} 

public void onClick_DeleteTasks(View v) { 
    myDB.deleteAll(); 
    populateListView(); 
} 

private void listViewItemLongClick() { 
    ListView myList = (ListView) findViewById(R.id.listViewTasks); 
    myList.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() { 

     @Override 
     public boolean onItemLongClick(AdapterView<?> adapterView, View view, int i, long id) { 
      myDB.deleteRow(id); 
      populateListView(); 

      return false; 
     } 
    }); 
} 

private void displayToast(long id) { 
    Cursor cursor = myDB.getRow(id); 
    if(cursor.moveToFirst()) { 
     long idDB = cursor.getLong(DBAdapter.COL_ROWID); 
     String task = cursor.getString(DBAdapter.COL_TASK); 
     String date = cursor.getString(DBAdapter.COL_DATE); 

     String message = "ID: " + idDB + "\n" + "Task: " + task + "\n" + "Date: " + date; 

     Toast.makeText(MainActivity.this, message, Toast.LENGTH_LONG).show(); 
    } 
    cursor.close(); 
} 

@Override 
protected void onDestroy() { 
    super.onDestroy(); 
    closeDB(); 
} 

private void closeDB() { 
    myDB.close(); 
}

}

第二活动：

import android.content.Intent; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.View; 
import android.widget.Button; 

public class MenuActivity extends AppCompatActivity { 

Button save; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_menu); 

    save = (Button) findViewById(R.id.buttonAddTask); 
    save.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      startActivity(new Intent(MenuActivity.this, MainActivity.class)); 
     } 
    }); 
}

}

来源

2016-07-28 Konrad

你的logcat是不相关的。这只是系统日志。 –

把代码放在问题中，避免将它们链接出来。如果链接中断，这个问题对任何人都没有什么帮助。 – petey

检查什么insertRow返回。如果它返回小于1，这意味着你不能插入。

来源

2016-07-28 14:32:15 faranjit

你的问题是ListView是空的。

在PopulateListView（）非常仔细一看：

public void populateListView() { 
    Cursor cursor = myDB.getAllRows(); 

    String[] fromFieldNames = new String[] { 
      DBAdapter.KEY_ROWID,DBAdapter.KEY_TASK,DBAdapter.KEY_DESCRIPTION 
    }; 

    int[] toViewIDs = new int[] { 
      R.id.textViewItemNumber, R.id.textViewItemTask, R.id.textViewItemDescription 
    }; 

    SimpleCursorAdapter myCursorAdapter; 
    myCursorAdapter = new SimpleCursorAdapter(getBaseContext(),R.layout.item_layout,cursor,fromFieldNames,toViewIDs,0); 
    ListView myList = (ListView)findViewById(R.id.listViewTasks); 
    myList.setAdapter(myCursorAdapter); 
}

一些线索

首先，你继续初始化myList中的ListView，每次调用该方法。在类实例化的时候做一次。为什么？因为你可能会用空的列表视图或其他东西来覆盖列表。我不知道，但这是一个线索。

其次，我没有看到如何将新项目添加到您的ListView。我看到你每次都设置适配器，但我没有看到添加。也许这只是我，但这是值得关注的。

现在，这里的一些快速的代码，我有一个更新的ListView

在OnCreate中（） - （一次性初始化），我有：

listView = (ListView) findViewById(R.id.mainListView); 
adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, listViewItems); 
listView.setAdapter(adapter);

后来的后来，在其他的代码，我想要添加项目我有以下代码：

// Add three generic items 
    for (int x = 0;x <=2;x++){ 
      adapter.add("test : " + String.valueOf(x)); 
     } 
    // let the adapter/view know the item list has changed so UI is updated. 
    adapter.notifyDataSetChanged();

这可能不是答案，但可能会帮助您到达那里。祝你好运。

来源

2016-07-28 14:53:26 raddevus

非常感谢您的时间，我确实尝试过您提到的所有内容，但正如我所说的，问题原来很愚蠢。看起来，在保存按钮的XML中，女巫在菜单布局中，我试图在主java文件中调用onClick_AddTask函数。我现在需要弄清楚如何从一个不同的布局文件的主java文件中访问一个函数，但我想这是一个不同的问题。 – Konrad

从SQLite数据库到其他活动的Android Studio ListView

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