Question

我正在使用GOOGLE_BOOK_API来解析JSON数据。当用户在搜索视图中输入不在列表中的关键字时，mEmptyStateTextView不起作用，表示没有找到书。下面是我的代码。

BookActivity.java //书籍详情

public class BookActivity extends AppCompatActivity {

/**
 * URL for book data from the google book dataset
 */
private static final String GOOGLE_REQUEST_SEARCH_URL = "https://www.googleapis.com/books/v1/volumes?maxResults=20&q=";
View loadingIndicator;
ArrayList<Book> books;
ConnectivityManager connectivityManager;
NetworkInfo networkInfo;
/**
 * Adapter for the list of earthquakes
 */
private BookAdapter mAdapter;
private TextView mEmptyStateTextView;

@Override
protected void onSaveInstanceState(Bundle keepState) {
    keepState.putParcelableArrayList("booklist", books);
    Log.v("My Log message", "book is :" + books);
    super.onSaveInstanceState(keepState);
}


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_book);
    loadingIndicator = findViewById(R.id.loading_indicator);
    loadingIndicator.setVisibility(View.GONE);

    // Find a reference to the {@link ListView} in the layout
    ListView bookListView = (ListView) findViewById(R.id.list);

    mEmptyStateTextView = (TextView) findViewById(R.id.empty_view);
    mEmptyStateTextView.setText(R.string.no_data);
    bookListView.setEmptyView(mEmptyStateTextView);

    // Create a new adapter that takes an empty list of books as input
    mAdapter = new BookAdapter(this, new ArrayList<Book>());

    // Set the adapter on the {@link ListView}
    // so the list can be populated in the user interface
    bookListView.setAdapter(mAdapter);

    if (savedInstanceState != null) {
        books = savedInstanceState.getParcelableArrayList("booklist");
        mAdapter.addAll(books);

    } else {
        books = new ArrayList<>();

    }
    bookListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
            Book currentBook = mAdapter.getItem(position);

            Uri bookUri = Uri.parse(currentBook.getUrl());

            Intent websiteIntent = new Intent(Intent.ACTION_VIEW, bookUri);

            startActivity(websiteIntent);
        }
    });


   /* if (networkInfo != null && networkInfo.isConnected()) {

        BookAsyncTask task = new BookAsyncTask();
        task.execute(GOOGLE_REQUEST_SEARCH_URL);
    } else {

        loadingIndicator = findViewById(R.id.loading_indicator);
        loadingIndicator.setVisibility(View.GONE);

        mEmptyStateTextView.setText(R.string.no_internet_connection);
    }*/
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.options_menu, menu);

    SearchManager searchManager =
            (SearchManager) getSystemService(Context.SEARCH_SERVICE);

    MenuItem searchItem = menu.findItem(R.id.search);
    final SearchView searchView = (SearchView) searchItem.getActionView();

    searchView.setSearchableInfo(searchManager.getSearchableInfo(getComponentName()));
    searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
        @Override
        public boolean onQueryTextSubmit(String query) {

            String urlQuery;
            query = searchView.getQuery().toString();

            connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);

            networkInfo = connectivityManager.getActiveNetworkInfo();
            if (networkInfo != null && networkInfo.isConnected()) {

                BookAsyncTask task = new BookAsyncTask();
                task.execute(GOOGLE_REQUEST_SEARCH_URL);

                if (!TextUtils.isEmpty(query)) {

                    String encodedQuery = "";
                    try {
                        encodedQuery = URLEncoder.encode(query, "utf-8");
                    } catch (UnsupportedEncodingException e) {
                        e.printStackTrace();
                    }
                    urlQuery = GOOGLE_REQUEST_SEARCH_URL + encodedQuery + "&maxResults=10";

                    //Toast.makeText(getApplicationContext(), urlQuery, Toast.LENGTH_SHORT).show();
                    mAdapter.clear();
                    mEmptyStateTextView.setText(""); // clear any message set previously
                    loadingIndicator.setVisibility(View.VISIBLE); // show loading during search
                    new BookAsyncTask().execute(urlQuery);
                }

            } else {

                Toast.makeText(getApplicationContext(), "Network not available", Toast.LENGTH_SHORT).show();
            }
            return true;
        }

        @Override
        public boolean onQueryTextChange(String newText) {

            return false;
        }
    });

    return true;
}

private class BookAsyncTask extends AsyncTask<String, Void, ArrayList<Book>> {
    @Override
    protected ArrayList<Book> doInBackground(String... urls) {

        if (urls.length < 1 || urls[0] == null) {
            return null;
        }

        ArrayList<Book> result = QueryUtils.fetchBook(urls[0]);
        return result;
    }

    @Override
    protected void onPostExecute(ArrayList<Book> result) {

        loadingIndicator = findViewById(R.id.loading_indicator);
        loadingIndicator.setVisibility(View.GONE);

        mAdapter.clear();

        if (result == null) {
            return;
        }
        if (result != null && !result.isEmpty()) {
            books = result;
            mAdapter.addAll(result);
        }

        mEmptyStateTextView.setText(R.string.no_book_found);

    }
}

}

activity_book.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">

<!-- Layout for a list of books -->
<ListView
    android:id="@+id/list"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:dividerHeight="0dp"
    android:divider="@null"/>

<!-- Empty view is only visible when the list has no items. -->
<TextView
    android:id="@+id/empty_view"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerInParent="true"
    android:paddingLeft="@dimen/padding_left"
    android:paddingRight="@dimen/padding_right"
    android:textAppearance="?android:textAppearanceMedium"/>

<!-- Loading indicator is only shown before the first load -->
<ProgressBar
    android:id="@+id/loading_indicator"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerInParent="true"/>

</RelativeLayout>

Answer 1

你在fetch url方法中两次调用BookAsyncTask，第一个是命中api https://www.googleapis.com/books/v1/volumes?maxResults=20&q=（这是错误的参数），第二个命中了正确的参数。

根据关于Asynctask的android指南（more details），一次只能执行一个Asynctask实例，所以第二个正确的URL永远不会被调用，你得到的响应命中第一个命中就是没有书结果

使用下面给出的方法替换onQueryTextSubmit完整方法，

public boolean onQueryTextSubmit(String query) {

        String urlQuery;
        query = searchView.getQuery().toString();

        connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);

        networkInfo = connectivityManager.getActiveNetworkInfo();
        if (networkInfo != null && networkInfo.isConnected()) {

            //BookAsyncTask task = new BookAsyncTask(); //Removing this and below will solve the problem
            //task.execute(GOOGLE_REQUEST_SEARCH_URL);//Removing this will solve the problem

            if (!TextUtils.isEmpty(query)) {

                String encodedQuery = "";
                try {
                    encodedQuery = URLEncoder.encode(query, "utf-8");
                } catch (UnsupportedEncodingException e) {
                    e.printStackTrace();
                }
                urlQuery = GOOGLE_REQUEST_SEARCH_URL + encodedQuery + "&maxResults=10";

                //Toast.makeText(getApplicationContext(), urlQuery, Toast.LENGTH_SHORT).show();
                mAdapter.clear();
                mEmptyStateTextView.setText(""); // clear any message set previously
                loadingIndicator.setVisibility(View.VISIBLE); // show loading during search
                new BookAsyncTask().execute(urlQuery);
            }

        } else {

            Toast.makeText(getApplicationContext(), "Network not available", Toast.LENGTH_SHORT).show();
        }
        return true;
    }

修改查看关于此link的非常好的教程，该教程使用GSON框架将JSON数据提取并解析为JAVA模型

解析JSON书籍数据时“没有找到书”逻辑在android中不起作用

1 个答案: