java - 我想将从字符串中获取的字符串传递给 onPostExecute 方法

Question

我是 android studio 的新手，想要更多东西。实际上，我试图将从 onCreateMethod 中的微调器获得的字符串传递给 onPostExecute 函数。我将非常感谢您的帮助。下面是我的代码。

我尝试创建一个名为 First 的全局变量，并存储来自 spinner 的字符串并将其传递给 onPostExecute 函数。

 public class Convert extends AppCompatActivity implements LocationListener 
{
  Spinner dropdown;
  Button btn;
  String text;
  String first;

 @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_convert);
    dropdown = (Spinner) findViewById(R.id.spinner1);
    btn = (Button)findViewById(R.id.btn);

String[] items = new String[]{"United States,USD", "Nepal,NPR", "Bangladesh,BDT","Brazil,BRL"};

    ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_spinner_dropdown_item, items);

    dropdown.setAdapter(adapter);

    btn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            text = dropdown.getSelectedItem().toString();
            first = text.substring(text.length()-3);
            Log.i("her", first);
        }
    });
  new DownloadTask().execute("http://openexchangerates.org/api/latest.json? 
  app_id=XXXXXXXXXX");


}

public class DownloadTask extends AsyncTask<String, Void, String> {
    @Override
    protected String doInBackground(String... urls) {


        String result = "";

        URL url;
        HttpURLConnection httpURLConnection = null;

        try {
            url = new URL(urls[0]);
            httpURLConnection = (HttpURLConnection) url.openConnection();

            InputStream in = httpURLConnection.getInputStream();

            InputStreamReader reader = new InputStreamReader(in);

            int data = reader.read();

            while (data != -1) {
                char counter = (char) data;
                result += counter;

                data = reader.read();
            }

            return result;


        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }


        return null;
    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);



        try{
            JSONObject jsonObject = new JSONObject(result);
            JSONObject curr = jsonObject.getJSONObject("rates");
            String npr = curr.getString(first);
            Log.i("money", npr );


        } catch (JSONException e) {
            e.printStackTrace();
        }
    }
}

我想要的是首先在 onPostExecute 函数上传递字符串。

Answer 1

当您调用 DownloadTask 时，asyncTask 会通过方法execute 触发，只需通过他传递参数即可。示例:

如何传递url

new DownloadTask().execute("url for download");

如何接收url

protected String doInBackground(String... urls) {
    String url = urls[0]; // url for download
}

您还可以发送参数数组。另外要小心 AsyncTask，不要传递上下文/ View 变量，它可能会导致内存泄漏，read docs .