ListView中没有任何内容，它没有加载内容

Question

我的书上市应用程序出现问题问题是我从https://www.googleapis.com/books/v1/volumes?q=android&maxResults=40 得到的json内容没有出现在列表视图中我现在不是什么这个理由可以帮助我吗？我面临艰难的时间来处理装载机:) BookActivity.java

package com.example.android.booklistingapp; 

import android.support.v4.app.LoaderManager; 
import android.support.v4.content.Loader; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.View; 
import android.widget.Button; 
import android.widget.EditText; 
import android.widget.ListView; 
import android.widget.Toast; 

import java.io.UnsupportedEncodingException; 
import java.net.URLEncoder; 
import java.util.ArrayList; 
import java.util.List; 

public class BookActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<List<VolumeInfo>> { 

    EditText searchFeild; 
    ListView booksListView; 
    BookApdapter apdapter; 
    String url ; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_book); 

     booksListView = (ListView) findViewById(R.id.MyList); 
     searchFeild = (EditText) findViewById(R.id.Search_EditText); 

     apdapter = new BookApdapter(this, new ArrayList<VolumeInfo>()); 
     booksListView.setAdapter(apdapter); 
     /* InputMethodManager inputMethodManager = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE); 
     inputMethodManager.hideSoftInputFromWindow(searchFeild.getWindowToken(), 0);*/ 

     Button searchButton = (Button) findViewById(R.id.Search_Button); 
     searchButton.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       String userInputSearchFeild = searchFeild.getText().toString().toLowerCase(); 
       Toast.makeText(getApplicationContext(), "yesssss", Toast.LENGTH_LONG).show(); 
       try { 
        userInputSearchFeild = URLEncoder.encode(userInputSearchFeild, "UTF-8"); 
        url = "https://www.googleapis.com/books/v1/volumes?q=" + userInputSearchFeild + "&maxResults=3"; 

       } catch (UnsupportedEncodingException e) { 
        Log.i("","Encode ERRor"); 
        e.printStackTrace(); 
       } 
      } 
     }); 
     LoaderManager loaderManager=getSupportLoaderManager(); 
     loaderManager.initLoader(0,null,BookActivity.this).forceLoad(); 
    } 

    @Override 
    public Loader<List<VolumeInfo>> onCreateLoader(int id, Bundle args) { 
     return new VolumeInfoLoader(this,url); 
    } 

    @Override 
    public void onLoadFinished(Loader<List<VolumeInfo>> loader, List<VolumeInfo> data) { 
     apdapter.clear(); 
     if(data != null && !data.isEmpty()) 
      apdapter.addAll(data); 
    } 

    @Override 
    public void onLoaderReset(Loader<List<VolumeInfo>> loader) { 
     apdapter.clear(); 
    } 
} 

volumeinfoloader.java

package com.example.android.booklistingapp; 


import android.support.v4.content.AsyncTaskLoader; 
import android.content.Context; 
import android.util.Log; 
import android.widget.Toast; 

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

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.List; 

/** 
* Created by Hazem_Khaled on 2017-10-12. 
*/ 

public class VolumeInfoLoader extends AsyncTaskLoader<List<VolumeInfo>> { 

    String mUrl; 

    public VolumeInfoLoader(Context context, String url) { 
     super(context); 
     mUrl = url; 
    } 

    @Override 
    protected void onStartLoading() { 
     forceLoad(); 
    } 

    @Override 
    public List<VolumeInfo> loadInBackground() { 
     if (mUrl == null) { 
      Log.i("This ", "null ERROR"); 
      return null; 
     } 
     try { 
      Toast.makeText(getContext(),"Start",Toast.LENGTH_LONG).show(); 
      URL url = new URL(mUrl); 
      HttpURLConnection connection = (HttpURLConnection) url.openConnection(); 
      connection.setReadTimeout(10000); 
      connection.setConnectTimeout(15000); 
      connection.setRequestMethod("GET"); 
      connection.connect(); 

      InputStream IS = connection.getInputStream(); 
      InputStreamReader ISR = new InputStreamReader(IS); 

      int data = ISR.read(); 
      String urlContent = ""; 
      Log.i("This is", urlContent); 
      while (data != -1) { 

       char c = (char) data; 
       urlContent += c; 
       data = ISR.read(); 
      } 

      Toast.makeText(getContext(),urlContent,Toast.LENGTH_LONG).show(); 
      JSONObject root = new JSONObject(urlContent); 
      JSONArray items = root.getJSONArray("item"); 
      List<VolumeInfo> booksInfo = new ArrayList<>(); 
      for (int i = 0; i < items.length(); i++) { 
       JSONObject volInfo = items.getJSONObject(i); 
       String bookTitle = volInfo.getString("title"); 
       String publisher = volInfo.getString("publisher"); 
       JSONArray authors = volInfo.getJSONArray("authors"); 

       StringBuilder authorsList = new StringBuilder(); 
       for (int j = 0; j < authors.length(); j++) { 
        authorsList.append("-" + authors.getString(i) + "\n"); 
       } 
       VolumeInfo volumeInfo = new VolumeInfo(bookTitle, publisher, authorsList); 
       booksInfo.add(volumeInfo); 
      } 
      return booksInfo; 

     } catch (MalformedURLException e) { 
      Log.i("This ", "URL ERROR"); 
      e.printStackTrace(); 
     } catch (JSONException e) { 
      Log.i("This ", "json ERROR"); 
      e.printStackTrace(); 
     } catch (IOException e) { 
      Log.i("This ", "io ERROR"); 
      e.printStackTrace(); 
     } 

     return null; 
    } 
} 

BookApdater.java

package com.example.android.booklistingapp; 

import android.app.Activity; 
import android.support.annotation.NonNull; 
import android.support.annotation.Nullable; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.ArrayAdapter; 
import android.widget.TextView; 

import java.util.ArrayList; 

/** 
* Created by Hazem_Khaled on 2017-10-06. 
*/ 

public class BookApdapter extends ArrayAdapter<VolumeInfo>{ 
    public BookApdapter(Activity context, ArrayList<VolumeInfo> booksInfo){ 
     super(context,0,booksInfo); 
    } 

    @NonNull 
    @Override 
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) { 

     View listView = convertView; 
     if (listView == null) 
      listView = LayoutInflater.from(getContext()).inflate(R.layout.author_list_item, parent, false); 


     VolumeInfo volumeInfo=getItem(position); 
     TextView bookTitle = (TextView) listView.findViewById(R.id.bookTitle_TextView); 
     TextView bookAuthors = (TextView) listView.findViewById(R.id.bookAuthors_TexttView); 
     TextView bookPublisher = (TextView) listView.findViewById(R.id.bookPublisher_TextView); 

     if(volumeInfo!=null) { 

      bookTitle.setText("Book Title:\n" + volumeInfo.getTitle() + "\n"); 

      StringBuilder authors = volumeInfo.getAuthorsList(); 
      bookAuthors.setText("Author(s):\n" + authors.toString() + "\n"); 
      bookPublisher.setText("Publisher:\n" + volumeInfo.getPublisher() + "\n"); 
     } 
     else{ 
      bookTitle.setText("there is no books for this category you have entered,please try valid category"); 
      bookAuthors.setText(""); 
      bookPublisher.setText(""); 
     } 

     return listView; 
    } 
} 

Answer 1

首先的URL被传递的null to VolumeInfoLoader： 这应该如何成为BookActivity：`public class BookActivity extends AppCompatA ctivity实现LoaderManager.LoaderCallbacks> {

EditText searchFeild; 
ListView booksListView; 
BookApdapter apdapter; 
String url ; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_book); 

    booksListView = (ListView) findViewById(R.id.MyList); 
    searchFeild = (EditText) findViewById(R.id.Search_EditText); 

    apdapter = new BookApdapter(this, new ArrayList<VolumeInfo>()); 
    booksListView.setAdapter(apdapter); 
    /* InputMethodManager inputMethodManager = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE); 
    inputMethodManager.hideSoftInputFromWindow(searchFeild.getWindowToken(), 0);*/ 

    Button searchButton = (Button) findViewById(R.id.Search_Button); 
    searchButton.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View v) { 
      String userInputSearchFeild = searchFeild.getText().toString().toLowerCase(); 
      Toast.makeText(getApplicationContext(), "yesssss", Toast.LENGTH_LONG).show(); 
      try { 
       userInputSearchFeild = URLEncoder.encode(userInputSearchFeild, "UTF-8"); 
       url = "https://www.googleapis.com/books/v1/volumes?q=" + userInputSearchFeild + "&maxResults=3"; 
       LoaderManager loaderManager=getSupportLoaderManager(); 
       loaderManager.initLoader(0,null,BookActivity.this).forceLoad(); 
      } catch (UnsupportedEncodingException e) { 
       Log.i("","Encode ERRor"); 
       e.printStackTrace(); 
      } 
     } 
    }); 

} 

@Override 
public Loader<List<VolumeInfo>> onCreateLoader(int id, Bundle args) { 
    Log.i("Loader"," onCreateLoader"); 

    return new VolumeInfoLoader(this,url); 

} 

@Override 
public void onLoadFinished(Loader<List<VolumeInfo>> loader, List<VolumeInfo> data) { 
    Log.i("Loader"," onLoadFinished"); 

    apdapter.clear(); 
    if(data != null && !data.isEmpty()) 
     apdapter.addAll(data); 
    apdapter.notifyDataSetChanged(); 
} 

@Override 
public void onLoaderReset(Loader<List<VolumeInfo>> loader) { 
    apdapter.clear(); 
    Log.i("Loader"," onLoaderReset"); 

} 

}`

基于API的 “https://www.googleapis.com/books/v1/volumes?q=arab&maxResults=10” 本次测试的第二：你必须正确地使用API​​：使用 JSONArray项目= root.getJSONArray （ “项目”）; 项目，而不是JSONArray项目= root.getJSONArray（ “项目”）; ... VolumeInfoLoader应该是这样的：'公共类VolumeInfoLoader扩展AsyncTaskLoader> {

String mUrl; 

public VolumeInfoLoader(Context context, String url) { 
    super(context); 
    mUrl = url; 
} 

@Override 
protected void onStartLoading() { 
    forceLoad(); 
} 

@Override 
public List<VolumeInfo> loadInBackground() { 
    if (mUrl == null) { 
     Log.i("This ", "null ERROR"); 
     return null; 
    } 
    try { 
     URL url = new URL(mUrl); 
     HttpURLConnection connection = (HttpURLConnection) url.openConnection(); 
     connection.setReadTimeout(10000); 
     connection.setConnectTimeout(15000); 
     connection.setRequestMethod("GET"); 
     connection.connect(); 

     InputStream IS = connection.getInputStream(); 
     InputStreamReader ISR = new InputStreamReader(IS); 

     int data = ISR.read(); 
     String urlContent = ""; 
     Log.i("This is", urlContent); 
     while (data != -1) { 

      char c = (char) data; 
      urlContent += c; 
      data = ISR.read(); 
     } 
     JSONObject root = new JSONObject(urlContent); 
     JSONArray items = root.getJSONArray("items"); 
     List<VolumeInfo> booksInfo = new ArrayList<>(); 
     for (int i = 0; i < items.length(); i++) { 
      JSONObject volInfo = items.getJSONObject(i); 
      volInfo=volInfo.getJSONObject("volumeInfo"); 
      String bookTitle = volInfo.getString("title"); 
      String publisher="Not Mention"; 
      if(volInfo.has("publisher")){ 
       publisher=volInfo.getString("publisher"); 
      } 

      JSONArray authors = volInfo.getJSONArray("authors"); 

      StringBuilder authorsList = new StringBuilder(); 
      for (int j = 0; j < authors.length(); j++) { 
       authorsList.append("-" + authors.getString(j) + "\n"); 
      } 
      VolumeInfo volumeInfo = new VolumeInfo(bookTitle, publisher, authorsList); 
      booksInfo.add(volumeInfo); 
     } 
     return booksInfo; 

    } catch (MalformedURLException e) { 
     Log.i("This ", "URL ERROR"); 
     e.printStackTrace(); 
    } catch (JSONException e) { 
     Log.i("This ", "json ERROR"); 
     e.printStackTrace(); 
    } catch (IOException e) { 
     Log.i("This ", "io ERROR"); 
     e.printStackTrace(); 
    } 

    return null; 
} 

}

`