如何在 Android 中的自定义 dapter 类中使用或实例化 Sqlite Database Helper 类实例? [英] How to use or instantiate Sqlite Database Helper class instance inside a custom dapter class in Android?
问题描述
我绝对是 Android 的初学者.现在我正在创建一个教程项目.在我的项目中，我将 ListView 与自定义适配器一起使用.但是我将自定义适配器创建为不同的独立文件，以使我的活动干净.但是当我在不同的文件中创建它时，我无法在自定义适配器中使用我的数据库助手类.
I am absolute beginner to Android. Now I am creating a tutorial project. In my project I am using ListView with custom adapter. But I created the custom adapter as a different and standalone file to make my activity clean. But when I create it in a different file, I cannot use my database helper class inside the custom adapter.
问题是我无法将 Activity 上下文传递给数据库助手类实例.在片段中，我可以通过调用这个method.getActivity().然后将它传递给我的数据库助手类的构造函数.如何在我的自定义适配器类中做同样的事情?
The problem is I cannot pass the Activity context to the database helper class instance. In fragment, I can pass by calling this method.getActivity(). Then pass it to the constructor of my database helper class. How can I do the same thing in my custom adapter class?
这是我的数据库助手类:
This is my database helper class:
public class DatabaseHelper extends SQLiteOpenHelper {
private static final int DATABASE_VERSION = 1;
private static final String DATABASE_NAME = "todo.db";
private static final String TABLE_NAME = "task";
private static final String COLUMN_ID = "id";
private static final String COLUMN_DESCRIPTION = "description";
private static final String COLUMN_DATE ="date";
private static final String COLUMN_DONE = "done";
private static final String CREATE_TABLE = "CREATE TABLE "+TABLE_NAME+" ("+COLUMN_ID+" INTEGER PRIMARY KEY AUTOINCREMENT,"+COLUMN_DESCRIPTION+" TEXT,"+
COLUMN_DATE+" DATE,"+COLUMN_DONE+" BOOLEAN)";
SQLiteDatabase db;
public DatabaseHelper(Context context)
{
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db)
{
this.db = db;
db.execSQL(CREATE_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
String query = "DROP TABLE IF EXISTS "+TABLE_NAME;
db.execSQL(query);
this.onCreate(db);
}
public void insertTask(Task task)
{
db = getWritableDatabase();
ContentValues values = new ContentValues();
values.put(COLUMN_DESCRIPTION,task.getDescription());
values.put(COLUMN_DATE,task.getDate());
values.put(COLUMN_DONE, Boolean.FALSE.toString());
db.insert(TABLE_NAME, null, values);
db.close();
}
public ArrayList<Task> getAllTasks()
{
ArrayList<Task> items = new ArrayList<Task>();
db = getReadableDatabase();
String query = "SELECT * FROM "+TABLE_NAME;
Cursor cursor = db.rawQuery(query,null);
if(cursor.moveToFirst())
{
do{
Task item = new Task();
item.setId(cursor.getInt(0));
item.setDescription(cursor.getString(1));
item.setDate(cursor.getString(2));
item.setDone(Boolean.valueOf(cursor.getString(3)));
items.add(item);
}
while (cursor.moveToNext());
}
return items;
}
public void markAsDone(int id){
db = getWritableDatabase();
ContentValues updatedData = new ContentValues();
updatedData.put(COLUMN_DONE, String.valueOf(Boolean.TRUE));
String where = COLUMN_ID+" = "+String.valueOf(id);
db.update(TABLE_NAME,updatedData,where,null);
}
}
这是我为 listView (TaskListAdapter.java) 定制的适配器类:
This is my custom adapter class for listView (TaskListAdapter.java):
public class TaskListAdapter extends ArrayAdapter<Task> {
private final Context context;
private final ArrayList<Task> values;
private DatabaseHelper dbHelper;
public TaskListAdapter(Context context,ArrayList<Task> values)
{
super(context,-1,values);
this.context = context;
this.values = values;
}
@Override
public View getView(int position,View convertView,ViewGroup parent)
{
LayoutInflater inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View rowView = inflater.inflate(R.layout.task_list_row,parent, false);
rowView.setTag(values.get(position).getId());
TextView rowDescription = (TextView)rowView.findViewById(R.id.task_row_description);
rowDescription.setText(values.get(position).getDescription());
ImageView rowStatusIcon = (ImageView)rowView.findViewById(R.id.task_row_status_icon);
Long currentDateMillSec= System.currentTimeMillis();
Long dateMillSec = CommonHelper.convertStrDateToMilSec(values.get(position).getDate());//(date==null)?0:date.getTime();
if(values.get(position).getDone()==Boolean.TRUE)
{
rowStatusIcon.setImageResource(R.drawable.done_icon);
}
else if(dateMillSec>0 && dateMillSec<currentDateMillSec)
{
rowStatusIcon.setImageResource(R.drawable.failed_icon);
}
else{
rowStatusIcon.setImageResource(R.drawable.todo_icon);
}
TextView dateTf = (TextView)rowView.findViewById(R.id.task_row_date);
dateTf.setText(values.get(position).getDate());
Button doneBtn = (Button)rowView.findViewById(R.id.task_row_done_btn);
doneBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//how can I instantiate the dbHelper class
//Then use the merkAsDone method here
}
});
return rowView;
}
}
如何在我的自定义适配器中实例化 dbHelper 属性，然后在完成按钮单击事件中调用 markAsDone 方法.在 Activity 中未创建适配器的情况下，如何实现它?
How can I instantiate the dbHelper property in my custom adapter and then call the markAsDone method in the done button click event. How can I achieve it whereas the adapter is not created within Activity?
推荐答案
看起来问题不大，在你的构造函数中实例化:
Does not look like a big problem, instantiate it in your constructor:
public TaskListAdapter(Context context,ArrayList<Task> values)
{
super(context,-1,values);
this.dbHelper = new DatabaseHelper(context.getApplicationContext());
this.context = context;
this.values = values;
}
然后在您的 OnClickListener 中使用它:
Then use it in your OnClickListener:
Button doneBtn = (Button)rowView.findViewById(R.id.task_row_done_btn);
doneBtn.setTag(values.get(position).getId());
doneBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
dbHelper.markAsDone(v.getTag());
}
});
不要忘记在 DatabaseHelper.markAsDone
这篇关于如何在 Android 中的自定义 dapter 类中使用或实例化 Sqlite Database Helper 类实例?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
