Question

我在Activity中使用了相同的代码并且它有效。但同样的事情在Fragment中不起作用。我已经进行了一些测试，以检查是否正确创建了数据库并发现cursor填充了数据。

以下是代码：

public class Db_fragment extends Fragment {
    View view;
    ListView listView;
    Db_listView_Adapter db_listView_adapter;

    public Db_fragment() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        view = inflater.inflate(R.layout.db_fragment, container, false);
        return view;
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        final MyDatabaseOpenHelper mDbHelper = new MyDatabaseOpenHelper(view.getContext());


        final EditText foodName = (EditText) view.findViewById(R.id.nameForDb);
        Button enterData = (Button) view.findViewById(R.id.enterData);
        Button showData = (Button) view.findViewById(R.id.showData);

        enterData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                SQLiteDatabase myDb = mDbHelper.getWritableDatabase();
                 ContentValues contentValues = new ContentValues();
                contentValues.put(TableFoodMacros.FoodMacros.FOOD_NAME,foodName.getText().toString());
                long newRowId ;
                newRowId = myDb.insert(TableFoodMacros.FoodMacros.TABLE_NAME,null,contentValues);
                Log.e("TEST1","TEST INSERT " + String.valueOf(newRowId));

            }
        });

        showData.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                SQLiteDatabase myDb = mDbHelper.getReadableDatabase();

                String[] projection = {"_id",TableFoodMacros.FoodMacros.FOOD_NAME};

                Cursor c = myDb.query(
                        TableFoodMacros.FoodMacros.TABLE_NAME,
                        projection,
                        null,
                        null,
                        null,
                        null,
                        null,
                        null
                );

                Log.e("TEST3", String.valueOf(c.getCount()));
                listView = (ListView) view.findViewById(R.id.dbView);
                db_listView_adapter = new Db_listView_Adapter(view.getContext(),c);
                listView.setAdapter(db_listView_adapter);

            }
        });

    }
}

应用程序在此行崩溃：

listView.setAdapter(db_listView_adapter);

Answer 1

您需要从findViewById dbView移除onClickListener的{{1}}并将其放入showData。

请删除以下内容。

onCreateView

将代码段放在showData.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View view) { // ... Remove the following code segment from here. listView = (ListView) view.findViewById(R.id.dbView); db_listView_adapter = new Db_listView_Adapter(view.getContext(),c); listView.setAdapter(db_listView_adapter); } });函数中。

onCreateView

它适用于您的@Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { view = inflater.inflate(R.layout.db_fragment, container, false); // Place the code segment here listView = (ListView) view.findViewById(R.id.dbView); db_listView_adapter = new Db_listView_Adapter(view.getContext(),c); listView.setAdapter(db_listView_adapter); return view; }，因为您在Activity中找不到ListView个ID。设置View的内容视图后，您可以将Activity放在任何位置，它会完美地找到关联的布局参考。

如果是findViewById，正如您所见，Fragment函数会返回onCreateView个对象作为View被夸大的引用。因此，您需要在View中找到ListView。这就是为什么您需要View来搜索view.findViewById中ListView的{{1}}的引用ID。

当您将View放入listView = (ListView) view.findViewById(R.id.dbView);时，它会获得按钮showData.setOnClickListener的引用，并尝试在showData中找到dbView导致错误的视图。

因此有必要在Button中获取列表的引用并在那里设置适配器。然后，当onCreateView填充数据时，您可以轻松调用notifyDatasetChanged()重新加载列表。

顺便说一句，您可以将代码段放在cursor函数中，因为您可以从那里获得onViewCreated按钮的引用而没有任何问题。所以你甚至可以把代码段放在那里。

showData

您可以像这样修改@Override public void onViewCreated(View view, @Nullable Bundle savedInstanceState) { super.onViewCreated(view, savedInstanceState); final MyDatabaseOpenHelper mDbHelper = new MyDatabaseOpenHelper(view.getContext()); final EditText foodName = (EditText) view.findViewById(R.id.nameForDb); Button enterData = (Button) view.findViewById(R.id.enterData); Button showData = (Button) view.findViewById(R.id.showData); // You can place the code segment here too listView = (ListView) view.findViewById(R.id.dbView); db_listView_adapter = new Db_listView_Adapter(view.getContext(),c); listView.setAdapter(db_listView_adapter); // ... Other code goes here. }

showData.setOnClickListener

setAdapter在片段Android中不起作用

1 个答案: