如何在Mainactivity和Android中的另一个类之间传递全局计数器？

Question

When i click on forward button it should increment page_counter, if there are no books to display it will put toast message, all this happens in onClick. When i click to go back, it decrements page counter, this happens in onClick too.

The problem is that i connect with ProcessData class(which loads book covers) only through execute() method which takes only one argument - search word("java" in this case)

How do i get this global-page_counter accessed from inside processdata class so i can load next/previous book covers?

public class MainActivity extends Activity {

int global_page_counter = 0 ;
@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_main);

    final ProcessData data = new ProcessData();
    // only search query goes into processdata!
    //how to pass/access more?
    data.execute("java");


    final ImageButton forward_button = (ImageButton)findViewById(R.id.forward_button);

    forward_button.setOnClickListener(new View.OnClickListener() {
        public void onClick(View arg0){

            if(data.isDataAvailable(search_query, global_page_counter) == false)
                Toast.makeText(getApplicationContext(),
                        "no more books", Toast.LENGTH_LONG).show();
            else {
                global_page_counter++ ;
                data.execute(search_query);
            }
        }
    });
    }


public class ProcessData extends AsyncTask<String, Void, String> {
private final String LOG_TAG = ProcessData.class.getSimpleName();

private List<Book> booksList ;

Uri destinationURL ;
public ProcessData(){
    booksList = new ArrayList<Book>();
    destinationURL = null ;
}


//checks if there is more images to load
public boolean isDataAvailable(String query, int page_counter){
     String validUrl = createValidURL(query, page_counter);
     if(validUrl.length() < 30) return false ;
  return true ;
}

 private String createValidUrl(String search_query){
     ......//some code here
}

//this method receives "java" search from execute() in mainActivity
public String doInBackground(String ...params) {

    String validUrl = createValidURL(params[0]  );//params[0] is java

 }
}

So basically, how do I pass another argument between classes if they connect only through 1 method taking 1 argument?

EDIT: for the user Dima, my code here

public class ProcessData extends AsyncTask<String, Void, String> {
private final String LOG_TAG = ProcessData.class.getSimpleName();

private List<Book> booksList ;
private static boolean isDataAvailable ;
private int page_count ;

Uri destinationURL ;
public ProcessData(){
    booksList = new ArrayList<Book>();
    destinationURL = null ;
}

public ProcessData(int page_counter, boolean isDataAvailable){
    booksList = new ArrayList<Book>();
    destinationURL = null ;
    page_count = page_counter;
    this.isDataAvailable = true ;
}

public static boolean getIsDataAvailable(){
    return isDataAvailable ;
}
public int get_page_counter(){
    return page_count ;
}

/*public boolean isDataAvailable(String query, int page_counter){
     String validUrl = createValidURL(query, page_counter);
     String bufferData = MakeConnectionAndStoreBufferData(validUrl);

     if(bufferData.length() < 30) return false ;
  return true ;
}*/

 private String createValidURL(String query, int page_counter) {
    String BASE_URL = "http://it-ebooks-api.info/v1/search";

    String resultUrl = null ;
    if (page_counter == 0){
        Log.d(LOG_TAG, "page is zero!");
        destinationURL = Uri.parse(BASE_URL).buildUpon()
                .appendPath(query)
                .appendQueryParameter("type", "title")
                .build();

    resultUrl = destinationURL.toString();
    resultUrl = resultUrl.replace("?", "&" );
  }
   else if(page_counter > 0){
        Log.d(LOG_TAG,"page is bigger than zero! page counter is: " +  page_counter);
        destinationURL = Uri.parse(BASE_URL).buildUpon()
                .appendPath(query)
                .appendQueryParameter( "type", "title")
                .appendQueryParameter("page",  Integer.toString(page_counter) )
                .build();

        resultUrl = destinationURL.toString();
        resultUrl = resultUrl.replace("?", "&");

    }

    return resultUrl ;
}

 private String MakeConnectionAndStoreBufferData(String validUrl){

  Log.d(LOG_TAG, "VALID url:" + validUrl);

HttpURLConnection urlConnection = null;
BufferedReader reader = null;

  try {
    URL url = new URL(validUrl);

    urlConnection = (HttpURLConnection) url.openConnection();
    if(urlConnection == null)
        Log.e(LOG_TAG, "url connection is null! ERROR");

    urlConnection.setRequestMethod("GET");

    try {
        urlConnection.connect();
    }catch(Exception e){
        Log.e(LOG_TAG, "exception : " + e );
    }

    InputStream inputStream = urlConnection.getInputStream();
    if(inputStream == null) {
        Log.e(LOG_TAG, "input stream failed to create!!!");
        return null;
    }
    StringBuffer buffer = new StringBuffer();

    reader = new BufferedReader(new InputStreamReader(inputStream));

    String line;
    while((line = reader.readLine()) != null) {
        buffer.append(line + "\n");
    }
        Log.d(LOG_TAG, " ");
    return buffer.toString();

} catch(IOException e) {
    Log.e(LOG_TAG, "Error", e);
    return null;
} finally {
    if(urlConnection != null) {
        urlConnection.disconnect();
    }
    if(reader != null) {
        try {
            reader.close();
        } catch(final IOException e) {
            Log.e(LOG_TAG,"Error closing stream", e);
        }
    }
  }
 }

public List<Book> getBooksList() {
    return booksList;
}

private void convertBufferDataIntoBook(String data) {

    final String BOOK_ID = "ID";
    final String BOOK_TITLE = "Title";
    final String BOOK_SUBTITLE = "SubTitle";
    final String BOOK_DESCRIPTION = "Description";
    final String BOOK_IMAGE = "Image";
    final String BOOK_ISBN = "isbn";

    //parsing raw buffer into clean nice Book object using json parser
    try {

        JSONObject jsonData = new JSONObject(data);
        JSONArray books_items = jsonData.getJSONArray("Books");

        for(int i=0; i<books_items.length(); i++) {

            JSONObject jsonBook = books_items.getJSONObject(i);

            long id = jsonBook.getLong(BOOK_ID);
            String book_title = jsonBook.getString(BOOK_TITLE);
            String book_subtitle = "";
            try {
                book_subtitle = jsonBook.getString(BOOK_SUBTITLE);
            }catch(JSONException e){
                   //sometime subtitle is missing!
                Log.d(LOG_TAG, "SUBTITLE IS MISSING NOW!");
                   book_subtitle = "N/A";
            }

            String book_description = jsonBook.getString(BOOK_DESCRIPTION);
            String book_image = jsonBook.getString(BOOK_IMAGE);
            String book_isbn = jsonBook.getString(BOOK_ISBN);

            Book book = new Book(id, book_title, book_subtitle, book_description, book_image, book_isbn);
            this.booksList.add(book);
        }
    } catch(JSONException jsone) {
        jsone.printStackTrace();
        Log.e(LOG_TAG,"Error processing Json data");
    }

}

public String doInBackground(String ...params) {


    String validUrl = createValidURL(params[0], get_page_counter()  );

    String result_buffer = MakeConnectionAndStoreBufferData(validUrl);
    if(result_buffer.length() < 30){
        isDataAvailable = false ;
        return "" ;
    }

    convertBufferDataIntoBook(result_buffer);

    return result_buffer;
  }

}

Answer 1

0) You should create ProcessData object every time you want to call execute.

1) You can make ProcessData inner class of MainActivity.

2) You can pass this counter to constructor of ProcessDataTask

Answer 2

您的数据加载类是内部类，因此只需将count创建为静态变量，

private static global_page_counter = 0