doinbackground 中的字符串变量值

Question

我正在使用解析数据填充列表视图，并且正在查询数据。我只想显示等于来自另一个活动的字符串的行。

我得到了字符串，因为我有一个显示字符串的 toast，但是 query.whereEqualTo 中的字符串是无效的。

如何在 doInBackground 中传递字符串变量的值？

这是我的代码，

公共类 ListadoMusica 扩展 Activity {

String año;
String artista;

// Declare Variables
ListView listview;
List<ParseObject> ob;
ProgressDialog mProgressDialog;
CustomAdapter adapter;
private List<Musica> musica = null;



@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // Get the view from listview_main.xml
    setContentView(R.layout.activity_listado_musica);

    año = getIntent().getStringExtra("myaño");
    artista = getIntent().getStringExtra("myartista");

    Toast.makeText(getApplicationContext(),año, Toast.LENGTH_SHORT).show();

    // Execute RemoteDataTask AsyncTask
    new RemoteDataTask().execute();


}


// RemoteDataTask AsyncTask
private class RemoteDataTask extends AsyncTask<Void, Void, Void> {
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // Create a progressdialog
        mProgressDialog = new ProgressDialog(ListadoMusica.this);
        // Set progressdialog title
        mProgressDialog.setTitle("Cargando...");
        // Set progressdialog message
        mProgressDialog.setMessage("Loading...");
        mProgressDialog.setIndeterminate(false);
        // Show progressdialog
        mProgressDialog.show();
    }

    @Override
    protected Void doInBackground(Void... params) {


        // Create the array
        musica = new ArrayList<Musica>();
        try {
            // Locate the class table named "Country" in Parse.com
            ParseQuery<ParseObject> query = new ParseQuery<ParseObject>(
                    "Musica");
            // Locate the column named "ranknum" in Parse.com and order list
            // by ascending
            //query.orderByAscending("createdAt");


            query.whereEqualTo("año", año);
            query.whereEqualTo("artista", artista);

            ob = query.find();
            for (ParseObject country : ob) {
                // Locate images in flag column
                ParseFile image = (ParseFile) country.get("imagen");

                Musica map = new Musica();
                map.setTitulo((String) country.get("titulo"));
                map.setArtista((String) country.get("artista"));
                map.setAño((String) country.get("año"));
                map.setFoto(image.getUrl());
                musica.add(map);
            }
        } catch (ParseException e) {
            Log.e("Error", e.getMessage());
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        // Locate the listview in listview_main.xml
        listview = (ListView) findViewById(R.id.listview);
        // Pass the results into ListViewAdapter.java
        adapter = new CustomAdapter(ListadoMusica.this,
                musica);
        // Binds the Adapter to the ListView
        listview.setAdapter(adapter);
        // Close the progressdialog
        mProgressDialog.dismiss();
    }
}

}

提前致谢，

Answer 1

修改这一行：

new RemoteDataTask().execute(año, artista );  

还有这一行：

private class RemoteDataTask extends AsyncTask<String, Void, Void> {

还有这一行：

protected Void doInBackground(String... params) {
   String año = params[0];
   String artista = params[1];
   //code
              query.whereEqualTo("año", año);

   //do whatever you need on artista 

Answer 2

我不太确定，为什么它在您提供的代码中是无效的，但是由于异步任务在另一个线程上执行，您不能保证您的活动实例（包括其内容）在任务运行时仍然有效。

可以肯定的是，将String año; 设为RemoteDataTask 的实例变量并将其传递给任务构造函数。

private class RemoteDataTask extends AsyncTask<Void, Void, Void> {
  private String año;

  RemoteDataTask(String año) {
    super();
    this.año = año;
  }
  ...
}

还要确保您的 Activity 能够优雅地处理方向变化。见this link