使用 SimpleCursor Loader 在 ListView 中显示元素

Question

我有以下片段，它出现在一个选项卡中。

public class Tab3Fragment extends Fragment {

    SQLiteDatabase db;
    DBHandler dbHandler =  new DBHandler(getContext(), null, null, 4);
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.tab3_frag, container, false);

        db = dbHandler.getReadableDatabase();

        String [] columns = {Contract.Student_Table.STUDENTS_COLUMN_ID, Contract.Student_Table.STUDENTS_COLUMN_NAME};
        Cursor mCursor = db.query(Contract.Student_Table.TABLE_NAME, columns, null,
                null, null, null, null);
        String[] from = new String[]{Contract.Student_Table.STUDENTS_COLUMN_NAME};
        int[] to = new int[]{R.id.student_view};

        SimpleCursorAdapter mCurAdapter = new SimpleCursorAdapter(getContext(),android.R.layout.simple_list_item_1, mCursor, from, to,0);

        ListView mMyListView = view.findViewById(R.id.simple_list);
        mMyListView.setAdapter(mCurAdapter);

        return view;
    }
}

我有以下 XML 文件 (tab3_frag)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#c2f6ff"
    android:orientation="vertical">

    <ListView
        android:id="@+id/simple_list"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <TextView
        android:id="@+id/student_view"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="TextView" />
</LinearLayout>

但是我的代码似乎不起作用，而且我无法发现错误。没有崩溃或错误，我的选项卡中什么也没有出现。如果能指导我解决我可能做错的问题，我将不胜感激。

Answer 1

改变这件事

 db = dbHandler.getReadableDatabase();

更改以下内容

像

一样为文本视图制作单独的布局

list_template.xml

<TextView
    android:id="@+id/student_view"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="TextView" />

然后改变这个东西..

int[] to = {R.id.student_view};

    SimpleCursorAdapter mCurAdapter = new SimpleCursorAdapter(getContext(),R.layout.list_template, mCursor, from, to,0);

Answer 2

下面class是一个单独的class用于执行所有操作。

public class DBHelper extends SQLiteOpenHelper{

//USER TABLE
public static final String USER_TABLE_NAME = "MyTableTwo";
public static final String USER_COLUMN_USER_ID = "id";
public static final String USER_COLUMN_USER_NAME = "Item_Name";
public static final String USER_COLUMN_USER_ADDRESS = "Weight";
public static final String USER_COLUMN_USER_CREATED_AT = "MRP";
public static final String USER_COLUMN_USER_UPDATED_AT = "BARCODE";

public DBHelper(Context context,
                String dbName,
                Integer version) {
    super(context, dbName, null, version);
}

@Override
public void onCreate(SQLiteDatabase db) {
    tableCreateStatements(db);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP TABLE IF EXISTS " + USER_TABLE_NAME);
    onCreate(db);
}

private void tableCreateStatements(SQLiteDatabase db) {
    try {
        db.execSQL(
                "CREATE TABLE IF NOT EXISTS "
                        + USER_TABLE_NAME + "("
                        + USER_COLUMN_USER_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "
                        + USER_COLUMN_USER_NAME + " VARCHAR(20), "
                        + USER_COLUMN_USER_ADDRESS + " VARCHAR(50), "
                        + USER_COLUMN_USER_CREATED_AT + " VARCHAR(10) DEFAULT " + getCurrentTimeStamp() + ", "
                        + USER_COLUMN_USER_UPDATED_AT + " VARCHAR(10) DEFAULT " + getCurrentTimeStamp() + ")"
        );

    } catch (SQLException e) {
        e.printStackTrace();
    }
}
public List<MyTableTwo> getMyItems() {
    List<MyTableTwo> mySuperList = new ArrayList<>();
    SQLiteDatabase db = this.getReadableDatabase();
    String selectQuery = "SELECT  * FROM " + USER_TABLE_NAME ;
    Cursor c = db.rawQuery(selectQuery, null);
    if (c != null) {
        c.moveToFirst();
        while (c.isAfterLast() == false) {
            MyTableTwo myTable = new MyTableTwo();
            myTable.itemName = (c.getString(c.getColumnIndex("Item_Name")));
            myTable.weight = (c.getString(c.getColumnIndex("Weight")));
            myTable.mrp = (c.getString(c.getColumnIndex("MRP")));
            myTable.barcod = (c.getString(c.getColumnIndex("BARCODE")));

            mySuperList.add(myTable);
            c.moveToNext();
        }
    }
    return mySuperList;
}

public Long insertUser(MyTableTwo user) throws Exception {
    try {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues contentValues = new ContentValues();
        contentValues.put(USER_COLUMN_USER_NAME, user.itemName);
        contentValues.put(USER_COLUMN_USER_ADDRESS, user.barcod);
        contentValues.put(USER_COLUMN_USER_CREATED_AT, user.weight);
        contentValues.put(USER_COLUMN_USER_UPDATED_AT, user.barcod);

        return db.insert(USER_TABLE_NAME, null, contentValues);
    } catch (Exception e) {
        e.printStackTrace();
        throw e;
    }
}

private String getCurrentTimeStamp() {
    return String.valueOf(System.currentTimeMillis() / 1000);
}

}

使用 SimpleCursor Loader 在 ListView 中显示元素

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