使用AsyncTask加载SQLite数据,我做错了什么?

时间:2017-07-21 09:20:00

标签: android android-asynctask android-sqlite loader

我是android和java的新手,我正在尝试实现异步加载器。但是没有加载数据。我在这里概念性地遗漏了什么吗?

我的活动:

public class TestActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<Cursor> {


ListView bookList;
MyCursorAdapter myAdapter;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_admin_library);
  //  dloader = new DBLoader(this);
    //dloader.loadInBackground();

   /* blah blah*/

    getSupportLoaderManager().initLoader(1,null,this);

    /* blah blah*/
    View header = (View) getLayoutInflater().inflate(R.layout.row_layout_title, null);
    TextView totals = header.findViewById(R.id.mainText);
    totals.setText("Total Books: " + Integer.toString(totalBooks));
    bookList.addHeaderView(header);

    bookList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {

            /* blah blah*/
            }


        }
    });
    /* blah blah*/
}

 /* blah blah*/

@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
   /*CursorLoader loader = new CursorLoader(this, null, null, null, null, null){
        @Override
        public Cursor loadInBackground(){
            DBHandler db = new DBHandler(getContext());
            return db.getCursor();
        }
   };*/
   DBLoader loader  = new DBLoader(this);
    return loader;
}

@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
    myAdapter = new MyCursorAdapter(this,data,0);
    bookList.setAdapter(myAdapter);
    // myAdapter.swapCursor(data);
    //myAdapter.notifyDataSetChanged();
}

@Override
public void onLoaderReset(Loader<Cursor> loader) {
    myAdapter.swapCursor(null);

}
}

DBLoader:

public class DBLoader extends AsyncTaskLoader<Cursor> {

private Cursor mCursor;
Context context;
public DBLoader(Context context) {
    super(context);
    this.context = context;
}

@Override
public Cursor loadInBackground() {
    DBHandler db = new DBHandler(context);
    Cursor cursor = db.getCursor();
    return cursor;
}

@Override
public void deliverResult(Cursor cursor){
    if(isReset()){
        releaseResources(cursor);
        return;
    }

    Cursor oldCursor = mCursor;
    mCursor = cursor;

    if(isStarted()){
        super.deliverResult(cursor);
    }

    if(oldCursor!=null && oldCursor!=cursor){
        releaseResources(oldCursor);
    }
}


private void releaseResources(Cursor cursor) {
    cursor.close();
}
}

我不知道我在这里是否缺少任何重要的电话,互联网上的大多数资源都是关于内容提供商(我不需要)。我只需要从本地SQLite数据库异步加载数据。

编辑:我的适配器:

public class MyCursorAdapter extends CursorAdapter {

private LayoutInflater cursorInflater;

public MyCursorAdapter(Context context, Cursor c, int flags) {
    super(context, c, flags);
    cursorInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}

@Override
public View newView(Context context, Cursor cursor, ViewGroup parent) {

    return cursorInflater.inflate(R.layout.row_layout, parent, false);
}

@Override
public void bindView(View v, Context context, Cursor cursor) {
    Log.d("Cursor :", cursor.getString(1));
    TextView title = (TextView) v.findViewById(R.id.listTitle);
    title.setText(cursor.getString(1));
    TextView author = (TextView) v.findViewById(R.id.listAuthor);
    author.setText(cursor.getString(2));
    TextView copies = (TextView) v.findViewById(R.id.listCopies);
    copies.setText(cursor.getString(5));

}

}

2 个答案:

答案 0 :(得分:0)

将您的DBLoader loader声明为全局变量

onCreateLoader

loader  = new DBLoader(this);
return loader;

将其放在onCreate方法而不是onLoadFinished

myAdapter = new MyCursorAdapter(this,null,0);
bookList.setAdapter(myAdapter);

将其放在onLoadFinishied

this.loader=(DBLoader)loader;
adapter.changeCursor(cursor);

答案 1 :(得分:0)

经过一番搜索,我在互联网上看到了一些他们使用的例子 一个getSupportLoaderManager().initLoader(1,null,this).forceLoad();。这似乎有效。同时在loader.forceLoad()中调用onCreateLoader()也可以。在进一步检查时,我看到了这一点:https://issuetracker.google.com/issues/36925900

我们似乎必须在forceLoad中实施onStartLoading(),因此:

protected void onStartLoading() { 
if (mCursor != null) { 
    deliverResult(mCursor); 
} 
if (takeContentChanged() || mCursor == null) { 
    forceLoad(); 
} 
} 

这样做将不再需要我们的活动中的.forceLoad()