Question

我在一个列表视图中点击了一个员工的行，然后将其传递回MainActivity。然后我尝试将其传递给另一个将更新其ListView并添加用户单击的行的适配器。我正在向数据库添加员工（可能不是最好的，因为他们已经在数据库中有一行）。然后我创建一个光标，抓住该行并尝试将theCursor更改为topAdapter（我正在尝试更新的listView适配器）。

我在topAdapter.changeCursor(clcikedEmployee):

上收到NullPointerException

我不认为创建新的TopListCursorAdapter会起作用，因为我不想创建新的TopListCursorAdapter，只需更新并将新行添加到其中的现有列表中。我知道e不是null，因为当我将它打印到控制台时，我正确地获得了被点击用户的数据。只是无法将其传递给TopAdapter以将行添加到现有列表视图中。

是否可以传递给TopFragment并从那里更新TopListCursorAdapter以将新行添加到列表中？

主要活动

public class MainActivity extends FragmentActivity implements BottomListViewAdapter.BottomListClickListener {
    private ProgressBar mProgressBar;
    EmployeeDBHandler dbHandler;
    private TopListCursorAdapter topAdapter;
    private BottomListViewAdapter bottomAdapter;
    private ArrayList<Employee> mEmployee;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mProgressBar = (ProgressBar) findViewById(R.id.progressBar);
        dbHandler = new EmployeeDBHandler(getApplicationContext());
        mProgressBar.setVisibility(View.VISIBLE);
        getXMLData();

        //GUI for seeing android SQLite Database in Chrome Dev Tools
        Stetho.InitializerBuilder inBuilder = Stetho.newInitializerBuilder(this);
        inBuilder.enableWebKitInspector(Stetho.defaultInspectorModulesProvider(this));
        Stetho.Initializer in = inBuilder.build();
        Stetho.initialize(in);
    }

    public void getXMLData() {
        OkHttpClient client = getUnsafeOkHttpClient();
        Request request = new Request.Builder()
                .url(getString(R.string.API_FULL_URL))
                .build();
        client.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                e.printStackTrace();
            }

            @Override
            public void onResponse(Call call, final Response response) throws IOException {
                final String responseData = response.body().string();
                final InputStream stream = new ByteArrayInputStream(responseData.getBytes());
                final XMLPullParserHandler parserHandler = new XMLPullParserHandler();
                final ArrayList<Employee> employees = (ArrayList<Employee>) parserHandler.parse(stream);

                for (Employee e : employees) {
                    dbHandler.addEmployee(e);
                }

                runOnUiThread(new Runnable() {
                    @Override
                    public void run() {
                        mProgressBar.setVisibility(View.GONE);
                        displayTopList();
                        displayBottomList();
                    }
                });
            }
        });
    }

    public void displayTopList() {
        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.topFragment, new TopFragment());
        fragmentTransaction.commit();
    }

    public void displayBottomList() {
        FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
        fragmentTransaction.replace(R.id.bottomFragment, new BottomFragment());
        fragmentTransaction.commit();
    }



@Override
public void onBottomListClick(Employee e) {
    dbHandler.addEmployee(e);
    Log.i("EMPLOYEE", e.toString());
    TopFragment topFragment = (TopFragment) getSupportFragmentManager().findFragmentById(R.id.topFragment);
    SQLiteDatabase db = dbHandler.getWritableDatabase();
    final Cursor clickedEmployee = db.rawQuery("SELECT * FROM " + "employees" + " WHERE " +
            "Employee_number" + "=" + e.getEmployee_number(), null);
    // change the adapter's Cursor
    topFragment.update(clickedEmployee);
}

}

TopFragment

public class TopFragment extends Fragment {
    public Cursor mTopCursor;
    EmployeeDBHandler dbHandler;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_top_list, container, false);
        String table = "employees";
        int mStartingEmployeeID = 3500075;
        dbHandler = new EmployeeDBHandler(getContext());
        SQLiteDatabase db = dbHandler.getWritableDatabase();
        mTopCursor = db.rawQuery("SELECT * FROM " + table + " WHERE " + "Employee_number" + "=" + mStartingEmployeeID, null);
        ListView mTopListView = (ListView) view.findViewById(R.id.mTopList);
        TopListCursorAdapter topAdapter = new TopListCursorAdapter(getContext(), mTopCursor);
        mTopListView.setAdapter(topAdapter);

        return view;
    }

public void update(Cursor cursor) {
        MergeCursor mergeCursor = new MergeCursor(new Cursor[]{
                        mTopCursor, cursor });
    }
}

底部碎片

public class BottomFragment extends Fragment {
    public Cursor mBottomCursor;
    EmployeeDBHandler dbHandler;

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_bottom_list, container, false);
        dbHandler = new EmployeeDBHandler(getContext());
        SQLiteDatabase db = dbHandler.getWritableDatabase();
        String table = "employees";
        int mStartingEmployeeID = 3500075;
        mBottomCursor = db.rawQuery("SELECT * FROM " + table + " WHERE " +
                "Employee_number" + "!=" + mStartingEmployeeID + " AND " +
                "Manager_employee_number" + "=" + mStartingEmployeeID + " ORDER BY " +
                "Last_name" + " ASC", null);
        ListView mBottomListView = (ListView) view.findViewById(android.R.id.list);
        BottomListViewAdapter mBottomAdapter = new BottomListViewAdapter(getContext(), mBottomCursor);
        mBottomListView.setAdapter(mBottomAdapter);
        return view;
    }
}

Answer 1

除非员工可以共享ID，否则此代码只会让您在ListView中显示一个员工。（在活动中）

dbHandler.addEmployee(e);
TopFragment topFragment = (TopFragment) getSupportFragmentManager().findFragmentById(R.id.topFragment);
SQLiteDatabase db = dbHandler.getWritableDatabase();
final Cursor clickedEmployee = db.rawQuery("SELECT * FROM " + "employees" + " WHERE " +
        "Employee_number" + "=" + e.getEmployee_number(), null);
// change the adapter's Cursor
topFragment.update(clickedEmployee);

此代码也将如此（在TopFragment中）

int mStartingEmployeeID = 3500075;
dbHandler = new EmployeeDBHandler(getContext());
SQLiteDatabase db = dbHandler.getWritableDatabase();
mTopCursor = db.rawQuery("SELECT * FROM " + table + " WHERE " + "Employee_number" + "=" + mStartingEmployeeID, null);
ListView mTopListView = (ListView) view.findViewById(R.id.mTopList);
TopListCursorAdapter topAdapter = new TopListCursorAdapter(getContext(), mTopCursor);
mTopListView.setAdapter(topAdapter);

您正在尝试向适配器添加行，而不是完全替换它。所以，要做到这一点，我认为你需要在你的任何数据交换混乱之前将INSERT语句放入数据库，然后重新编写查询，以便所有结果你正在尝试插入将返回。

例如，如果ID自动递增，您可能需要WHERE Employee_number >= " + mStartingEmployeeID。

此外，这可能无法解决某些问题，您违反了dbHandler实例的目的，即＆＃34;封装＆＃34;你的疑问。

所以，而不是这个

SQLiteDatabase db = dbHandler.getWritableDatabase();
mTopCursor = db.rawQuery("SELECT * FROM " + table + " WHERE " + "Employee_number" + "=" + mStartingEmployeeID, null);

推荐方式只是

topCursor = dbHandler.getEmployeeWithId(mStartingEmployeeID);

如果您已经有类似的方法返回Employee，那么您可以改为使用Employee(Cursor c)构造函数，而不是像这样使用

Employee e = new Employee(dbHandler.getEmployeeWithId(mStartingEmployeeID));

Answer 2

所以我能够让它最终发挥作用。我所做的是从bottomList获取光标，将其与TopLists现有光标合并，然后将该光标传递给TopAdapter。

public void update(Cursor cursor) {
        MergeCursor mergeCursor = new MergeCursor(new Cursor[]{cursor, mTopCursor});
        TopListCursorAdapter topAdapter = new TopListCursorAdapter(getContext(), mergeCursor);
        mTopListView.setAdapter(topAdapter);
    }

发送光标以添加到另一个列表视图

2 个答案: