java - ListView 没有在 fragment 中更新

Question

我确信 updateFromDatabase() 函数可以工作，我已经使用 print 语句来查看放入 mCooperativesArray 中的条目是否存在，而不是空字符串。但是，当我重新启动应用程序时， fragment 永远不会使用数据库中的项目填充 ListView 。我认为这与 fragment 生命周期有关，但我不知道。

此外，当我不重新启动应用程序并首次运行它时， ListView 运行良好。当我旋转或重新启动应用程序时， ListView 不再填充。

public class LocalFragment extends Fragment{

private ListView mLocalList;
private ArrayAdapter<String> adapter;
private ArrayList<String> mCoordinatesArray;
private BroadcastReceiver mBroadcastReceiver;
private LocationBaseHelper mDatabase;
private DateFormat dateFormat;
private String dateString;

@Override
public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){
    View v = inflater.inflate(R.layout.fragment_local,container,false);
    // SQLite Setup
    mDatabase = new LocationBaseHelper(getActivity());

    mLocalList = (ListView) v.findViewById(R.id.lv_local);
    mCoordinatesArray = new ArrayList<>();
    adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, mCoordinatesArray);
    if(!mDatabase.size().equals("0")){
        updateFromDatabase();
    }
    mLocalList.setAdapter(adapter);
    return v;
}

@Override
public void onResume() {
    super.onResume();

    if(mBroadcastReceiver == null){
        mBroadcastReceiver = new BroadcastReceiver() {
            @Override
            public void onReceive(Context context, Intent intent) {
                dateFormat = new SimpleDateFormat("MM/dd HH:mm:ss a");
                dateString = dateFormat.format(new Date());

                String[] data = intent.getStringExtra("coordinates").split(" ");
                mDatabase.insertEntry(dateString,data[0],data[1]);
                System.out.println(mDatabase.size());

                mCoordinatesArray.add(dateString + " " + data[0] + " " + data[1]);
                adapter.notifyDataSetChanged();
            }
        };
    }
    getActivity().registerReceiver(mBroadcastReceiver, new IntentFilter("location_update"));
}

@Override
public void onDestroy() {
    super.onDestroy();
    if(mBroadcastReceiver!=null){
        getActivity().unregisterReceiver(mBroadcastReceiver);
    }
}

// THIS METHOD CAN BE USED TO UPDATE THE ARRAY HOLDING COORDINATES FROM THE LOCAL DATABASE
private void updateFromDatabase(){
    //mCoordinatesArray.clear();
    mCoordinatesArray = mDatabase.getEntireDatabase();
    adapter.notifyDataSetChanged();
}

}

这是我的 Helper 类，以防万一，但我认为问题不在这里。

public class LocationBaseHelper extends SQLiteOpenHelper {

private static final int VERSION = 1;
private static final String D​A​T​A​B​A​S​E​_​N​A​M​E​ = "locationBase.db";

public LocationBaseHelper(Context context) {
    super(context, D​A​T​A​B​A​S​E​_​N​A​M​E​, null, VERSION);
}

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL("create table " +    LocationTable.NAME              + " ("      +
                                    LocationTable.Cols.DATE_TIME    + " text, " +
                                    LocationTable.Cols.LATITUDE     + " text, " +
                                    LocationTable.Cols.LONGITUDE    + " text )"
    );
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

}

public void insertEntry(String date_time, String latitude, String longitude){
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues content = new ContentValues();
    content.put(LocationTable.Cols.DATE_TIME,date_time);
    content.put(LocationTable.Cols.LATITUDE,latitude);
    content.put(LocationTable.Cols.LONGITUDE,longitude);
    db.insert(LocationTable.NAME,null,content);
}

public ArrayList<String> getEntireDatabase(){
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery("SELECT * FROM " + LocationTable.NAME,null);
    cursor.moveToFirst();

    ArrayList<String> values = new ArrayList<>();

    do{
        String value = (String) cursor.getString(cursor.getColumnIndex(LocationTable.Cols.DATE_TIME)) + " " +
                       (String) cursor.getString(cursor.getColumnIndex(LocationTable.Cols.LATITUDE))  + " " +
                       (String) cursor.getString(cursor.getColumnIndex(LocationTable.Cols.LONGITUDE));
        values.add(0,value);

    }while(cursor.moveToNext());

    return values;
}

public String size(){
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery("SELECT COUNT(*) FROM " + LocationTable.NAME,null);
    cursor.moveToFirst();
    return cursor.getString(0);
}
}

Answer 1

通过调用mCooperativesArray = mDatabase.getEntireDatabase();，您正在更改mCooperativesArray的引用，并且适配器仍然保留旧的引用，因此它看不到任何变化。

您应该只更新它包含的值，而不是创建 mCooperativeArray 的新实例，例如:

mCoordinateArray.clear();
mCoordinateArray.addAll(mDatabase.getData());
adapter.notifyDataSetChange();

这样您就可以更改适配器引用的数据，而不是创建适配器不知道的全新数据集。