ListView未从适配器填充

时间：2017-07-13 05:20:39

标签： android json listview android-arrayadapter google-books

这个应用程序用于使用Google Books API将书籍作为JSON获取，并且在研究中我还发现JSON数据正在加载正常，书籍标题，作者被正确解析并且我使用祝酒词进行了测试。但是，即使使用适配器设置listView，listView也不会显示。什么一定是错误的？该应用程序也没有崩溃使得排除故障变得困难。提前谢谢！

主要活动 

package com.praveent.booklisting;

import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.net.Uri;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Toast;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Scanner;

public class MainActivity extends AppCompatActivity {

    public String rootUrl = "https://www.googleapis.com/books/v1/volumes";
    public String queryParameter = "q";
    Button search_button;
    EditText search_string;
    ListView listView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listView = (ListView) findViewById(R.id.list_view);
        search_button = (Button) findViewById(R.id.search_button);
        search_string = (EditText) findViewById(R.id.search_string);
        search_button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String query = search_string.getText().toString();
                ConnectivityManager connectivityManager
                        = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
                NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();
                if(activeNetworkInfo != null && activeNetworkInfo.isConnected()){
                    new BackgroundTask().execute(query);
                }
                else{
                    Toast.makeText(MainActivity.this, "Please switch on the internet!", Toast.LENGTH_SHORT).show();
                }
            }
        });

    }

    public void populate(BookAdapter adapter){
        listView.setAdapter(adapter);
    }

    public class BackgroundTask extends AsyncTask<String, JSONArray, String> {

        @Override
        protected String doInBackground(String... strings) {
            String query = strings[0];
            URL url = null;
            Uri uri = Uri.parse(rootUrl).buildUpon().appendQueryParameter(queryParameter, query).build();
            try {
                url = new URL(uri.toString());
            } catch (MalformedURLException e) {
                e.printStackTrace();
            }
            String data = null;
            try {
                HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
                InputStream in = urlConnection.getInputStream();
                Scanner scanner = new Scanner(in);
                scanner.useDelimiter("\\A");
                if(scanner.hasNext()){
                    data = scanner.next();
                }
            } catch (IOException e1) {
                e1.printStackTrace();
            }
            return data;
        }

        @Override
        protected void onPostExecute(String s) {
            super.onPostExecute(s);
            BookAdapter bookAdapter;
            JSONObject jsonObject = null;
            JSONArray jsonArray = null;
            JSONObject jsonArrayObject = null;
            JSONObject volumeInfo = null;
            JSONArray authorInfo = null;
            JSONObject imageInfo = null;
            String imageUrl = null;
            String bookTitle = null;
            String bookAuthor = null;
            try {
                jsonObject = new JSONObject(s);
                jsonArray = jsonObject.getJSONArray("items");
                ArrayList<Book> books= new ArrayList<Book>();
                for(int i = 0; i <= jsonArray.length(); i++){
                    jsonArrayObject = jsonArray.getJSONObject(i);
                    volumeInfo = jsonArrayObject.getJSONObject("volumeInfo");
                    bookTitle = volumeInfo.getString("title");
                    authorInfo = volumeInfo.getJSONArray("authors");
                    bookAuthor = " ";
                    if (authorInfo != null){
                        bookAuthor = authorInfo.getString(0);
                    }
                    //imageInfo = volumeInfo.getJSONObject("imageLinks");
                    //imageUrl = imageInfo.getString("smallThumbnail");
                    books.add(new Book(bookTitle, bookAuthor));
                    Toast.makeText(MainActivity.this, bookAuthor, Toast.LENGTH_SHORT).show();
                }
                bookAdapter = new BookAdapter(MainActivity.this, books);
                populate(bookAdapter);
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    }
}

书籍适配器 

package com.praveent.booklisting;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;
import com.squareup.picasso.Picasso;
import java.util.ArrayList;

public class BookAdapter extends ArrayAdapter<Book>{

    Context c = null;
    public BookAdapter(Context context, ArrayList<Book> books) {
        super(context, 0, books);
        c = context;
    }
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        View listItemView = convertView;
        if (listItemView == null) {
            listItemView = LayoutInflater.from(getContext()).inflate(
                    R.layout.list_item, parent, false);
        }
        Book currentBook = getItem(position);
        TextView bookTextView = (TextView) listItemView.findViewById(R.id.book_name);
        bookTextView.setText(currentBook.getBookName());
        TextView authorTextView = (TextView) listItemView.findViewById(R.id.book_author);
        authorTextView.setText(currentBook.getAuthorName());
        //ImageView coverImageView = (ImageView) listItemView.findViewById(R.id.cover_image);
        //Picasso.with(c).load(currentBook.getImageURL()).into(coverImageView);
        return listItemView;
    }
}

图书类 

package com.praveent.booklisting;

public class Book {

    private String bookName;
    private String authorName;
    private String imageURL;

    public Book(String name, String author){
        bookName = name;
        authorName = author;
        //imageURL = url;
    }

    public String getBookName() {
        return bookName;
    }

    public String getAuthorName() {
        return authorName;
    }

    public String getImageURL() {
        return imageURL;
    }
}

activity_main.xml中 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:orientation="vertical"
    android:layout_height="match_parent"
    tools:context="com.praveent.booklisting.MainActivity">

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="16dp"
        android:id="@+id/search_string"
        android:textAlignment="center"
        android:gravity="center"
        android:hint="@string/search_hint"/>

    <Button
        android:layout_width="match_parent"
        android:id="@+id/search_button"
        android:layout_height="wrap_content"
        android:text="@string/search_button" />
    <ListView
        android:layout_width="fill_parent"
        android:id="@+id/list_view"
        android:layout_height="fill_parent">
    </ListView>

</LinearLayout>

list_item.xml 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal" android:layout_width="match_parent"
    android:padding="8dp"
    android:layout_height="wrap_content">

    <ImageView
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:id="@+id/cover_image"/>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginLeft="8dp"
        android:layout_gravity="center"
        android:orientation="vertical">

        <TextView
            android:id="@+id/book_name"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:textColor="#000"
            android:textSize="18sp"
            android:textStyle="bold" />

        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:textSize="16sp"
            android:textColor="#000"
            android:id="@+id/book_author"/>
    </LinearLayout>

</LinearLayout>

3 个答案:

答案 0 :(得分：2)

关于PostExecute Change for(int i = 0; i <=jsonArray.length(); i++) 到for(int i = 0;i<jsonArray.length(); i++) 在list_item.xml上，将文本颜色更改为白色

答案 1 :(得分：-1)

你需要在适配器中调用getCount（）。

public class BookAdapter extends ArrayAdapter<Book>{

Context c = null;
ArrayList<Book> bookslist = new ArrayList();
public BookAdapter(Context context, ArrayList<Book> books) {
    super(context, 0, books);
    c = context;
    bookslist = books;
}

@Override
public int getCount() {
    return bookslist.size();
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View listItemView = convertView;
    if (listItemView == null) {
        listItemView = LayoutInflater.from(getContext()).inflate(
                R.layout.list_item, parent, false);
    }
    Book currentBook = getItem(position);
    TextView bookTextView = (TextView) listItemView.findViewById(R.id.book_name);
    bookTextView.setText(currentBook.getBookName());
    TextView authorTextView = (TextView) listItemView.findViewById(R.id.book_author);
    authorTextView.setText(currentBook.getAuthorName());
    //ImageView coverImageView = (ImageView) listItemView.findViewById(R.id.cover_image);
    //Picasso.with(c).load(currentBook.getImageURL()).into(coverImageView);
    return listItemView;
}

}

答案 2 :(得分：-1)

将适配器更改为此

public class BookAdapter extends ArrayAdapter<Book> {

Context c = null;
private List<Book> bookList;

public BookAdapter(Context context, ArrayList<Book> books) {
    super(context, 0, books);
    c = context;
    bookList = new ArrayList<>();
    bookList = books;
}

@Override
public int getCount() {
    return bookList.size();
}

@Nullable
@Override
public Book getItem(int position) {
    return bookList.get(position);
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View listItemView = convertView;
    if (listItemView == null) {
        listItemView = LayoutInflater.from(getContext()).inflate(
                R.layout.list_item, parent, false);
    }
    Book currentBook = getItem(position);
    TextView bookTextView = (TextView) listItemView.findViewById(R.id.book_name);
    bookTextView.setText(currentBook.getBookName());
    TextView authorTextView = (TextView) listItemView.findViewById(R.id.book_author);
    authorTextView.setText(currentBook.getAuthorName());
    //ImageView coverImageView = (ImageView) listItemView.findViewById(R.id.cover_image);
    //Picasso.with(c).load(currentBook.getImageURL()).into(coverImageView);
    return listItemView;
}

}

我检查了你的代码错误是在AsyncTask onPostExecute方法中，将你的for循环条件改为

for（int i = 0; i＆lt; jsonArray.length（）; i ++）

现在正在运作。

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