如何在安卓应用程序中通过回收器视图显示外部SQLite数据库数据

Question

最近几天，我学会了如何使用SQLiteOpenHelper创建SQLite数据库并通过RecyclerView显示它。是的，通过谷歌和Stack-overflow的力量，我已经很好地学习了它。但是，我现在通过回收器视图显示外部数据库数据时遇到了一些麻烦。最近两天我搜索了很多，大多数只是通过使用"资产文件夹和SQLiteAssetsHelper"将外部数据库导入应用程序。那么，您能否给我一些通过回收器视图显示外部SQLite数据库数据的指南？任何链接或任何书籍或任何参考资料将不胜感激。提前谢谢。

Answer 1

作为与数据库交互的结果，use 应该获取一个数据集(数组或像 ArrayList 这样的集合(。正如我所看到的，从您的解释中，您现在知道如何获取它，但不知道如何将其传递给您的回收器View。所以你需要一个适配器来做到这一点。适配器是一个类，将从数组数据集中获取每个对象，并从其数据中创建(膨胀(单个回收器视图项。处理完所有数组项后，适配器将生成一个项列表，这样它将用数据填充回收器视图，下面是一个代码片段，可以帮助您了解它的工作原理：

<android.support.v7.widget.RecyclerView
android:id="@+id/my_recycler_view"
android:scrollbars="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"/>

 public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {
    private String[] mDataset;
    // Provide a reference to the views for each data item
    // Complex data items may need more than one view per item, and
    // you provide access to all the views for a data item in a view holder
    public static class MyViewHolder extends RecyclerView.ViewHolder {
        // each data item is just a string in this case
        public TextView textView;
        public MyViewHolder(TextView v) {
            super(v);
            textView = v;
        }
    }

    // Provide a suitable constructor (depends on the kind of dataset)
    public MyAdapter(String[] myDataset) {
        mDataset = myDataset;
    }
    // Create new views (invoked by the layout manager)
    @Override
    public MyAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent,
                                                   int viewType) {
        // create a new view
        TextView v = (TextView) LayoutInflater.from(parent.getContext())
                .inflate(R.layout.my_text_view, parent, false);
        ...
        MyViewHolder vh = new MyViewHolder(v);
        return vh;
    }
    // Replace the contents of a view (invoked by the layout manager)
    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        // - get element from your dataset at this position
        // - replace the contents of the view with that element
        holder.textView.setText(mDataset[position]);
    }
    // Return the size of your dataset (invoked by the layout manager)
    @Override
    public int getItemCount() {
        return mDataset.length;
    }
}

    public class MyActivity extends Activity {
    private RecyclerView recyclerView;
    private RecyclerView.Adapter mAdapter;
    private RecyclerView.LayoutManager layoutManager;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.my_activity);
        recyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);
        // use this setting to improve performance if you know that changes
        // in content do not change the layout size of the RecyclerView
        recyclerView.setHasFixedSize(true);
        // use a linear layout manager
        layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);
        // specify an adapter (see also next example)
        mAdapter = new MyAdapter(myDataset);
        recyclerView.setAdapter(mAdapter);
    }
    // ...
}