java - eclipse 安卓 : JSONAdapter not updating ListView

Question

我正在学习本教程:http://www.raywenderlich.com/56111/make-first-android-app-part-3

我们正在使用带有 JSONAdapter 的异步 Http，并尝试在 ListView 中显示图书数据。

问题是单击“搜索”按钮时没有任何反应。该列表甚至不会弹出。

这是我的 MainActivity.java 代码:

package com.example.newapp;

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

import org.json.JSONObject;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.ShareActionProvider;
import android.widget.TextView;
import android.widget.Toast;

import com.loopj.android.http.AsyncHttpClient;
import com.loopj.android.http.JsonHttpResponseHandler;

public class MainActivity extends Activity implements View.OnClickListener, OnItemClickListener {

    TextView mainTextView;
    Button mainButton;
    EditText mainEditText;
    ListView mainListView;
    JSONAdapter mJSONAdapter;
    ArrayList mNameList = new ArrayList();
    ShareActionProvider mShareActionProvider;
    private static final String PREFS = "prefs";
    private static final String PREF_NAME = "name";
    SharedPreferences mSharedPreferences;
    private static final String QUERY_URL = "http://openlibrary.org/search.json?q=";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mainEditText = (EditText)findViewById(R.id.main_edittext);
        mainTextView = (TextView)findViewById(R.id.main_textview);
        mainButton = (Button)findViewById(R.id.main_button);
        mainButton.setOnClickListener(this);
        mainListView = (ListView)findViewById(R.id.main_listview);
        mainListView.setOnItemClickListener(this);
        displayWelcome();
        // 10. Create a JSONAdapter for the ListView
        mJSONAdapter = new JSONAdapter(this, getLayoutInflater());

        // Set the ListView to use the ArrayAdapter
        mainListView.setAdapter(mJSONAdapter);

    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        MenuItem shareItem = menu.findItem(R.id.menu_item_share);
        if (shareItem != null) {
            mShareActionProvider = (ShareActionProvider)shareItem.getActionProvider();
        }
        setShareIntent();
        return true;
    }

    private void setShareIntent() {

        if (mShareActionProvider != null) {

            // create an Intent with the contents of the TextView
            Intent shareIntent = new Intent(Intent.ACTION_SEND);
            shareIntent.setType("text/plain");
            shareIntent.putExtra(Intent.EXTRA_SUBJECT, "Android Development");
            shareIntent.putExtra(Intent.EXTRA_TEXT, mainTextView.getText());

            // Make sure the provider knows
            // it should work with that Intent
            mShareActionProvider.setShareIntent(shareIntent);
        }
        }


    @Override
    public void onClick(View v) {
        queryBooks(mainEditText.getText().toString());
        mainEditText.setText("");
    }

    @Override 
    public void onItemClick(AdapterView parent, View view, int position, long id) {
        // Log the item's position and contents
        // to the console in Debug

    }

    public void displayWelcome(){
        mSharedPreferences = getSharedPreferences(PREFS, MODE_PRIVATE);
        String name = mSharedPreferences.getString(PREF_NAME, "");
        if (name.length() > 0){
            Toast.makeText(this, "Welcome back, " + name + "!", Toast.LENGTH_SHORT).show();
        } 
        else {
            AlertDialog.Builder alert = new AlertDialog.Builder(this);
            alert.setTitle("Hello!");
            alert.setMessage("What is your name?");

            final EditText input = new EditText (this);
            alert.setView(input);

            alert.setPositiveButton("OK", new DialogInterface.OnClickListener() {

                public void onClick(DialogInterface dialog, int whichButton) {
                    String inputName = input.getText().toString();
                    SharedPreferences.Editor e = mSharedPreferences.edit();
                    e.putString(PREF_NAME, inputName);
                    e.commit();

                    Toast.makeText(getApplicationContext(), "Welcome, " + inputName + "!", 
                            Toast.LENGTH_LONG).show();
                }
            });

            alert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {

                @Override
                public void onClick(DialogInterface dialog, int whichButton) {
                    // TODO Auto-generated method stub

                }
            });
            alert.show();
        }
    }

    private void queryBooks(String searchString) {
        String urlString = "";
        try {
            urlString = URLEncoder.encode(searchString, "UTF-8");
        }
        catch (UnsupportedEncodingException e) {
            e.printStackTrace();
            Toast.makeText(this, "Error: " + e.getMessage(), Toast.LENGTH_LONG).show();

        }

        AsyncHttpClient client = new AsyncHttpClient();
        client.get(QUERY_URL + urlString, new JsonHttpResponseHandler(){

            public void onSuccess (JSONObject jsonObject) {
                //Display a Toast message
                //to announce your succcess
                Toast.makeText(getApplicationContext(), "Success!", Toast.LENGTH_LONG).show();
                mJSONAdapter.updateData(jsonObject.optJSONArray("docs"));
            }
            public void onFailure (int statusCode, Throwable throwable, JSONObject error) {
                Toast.makeText(getApplicationContext(), "Error: " + statusCode + " " + 
                        throwable.getMessage(), Toast.LENGTH_LONG).show();
                Log.e("omg android", statusCode + " " + throwable.getMessage());
            }
        });
    }
}

这里是 JSONAdapter.java:

package com.example.newapp;

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

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import com.squareup.picasso.Picasso;

public class JSONAdapter extends BaseAdapter {

    private static final String IMAGE_URL_BASE = "http://covers.openlibrary.org/b/id/";

    Context mContext;
    LayoutInflater mInflater;
    JSONArray mJsonArray;

    public JSONAdapter (Context context, LayoutInflater inflater) {
        mContext = context;
        mInflater = inflater;
        mJsonArray = new JSONArray();
    }



    @Override
    public int getCount() {

        return mJsonArray.length();
    }

    @Override
    public JSONObject getItem(int position) {

        return mJsonArray.optJSONObject(position);
    }

    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;

        // check if the view already exists
        // if so, no need to inflate and findViewById again!
        if (convertView == null) {

            // Inflate the custom row layout from your XML.
            convertView = mInflater.inflate(R.layout.row_book, null);

            // create a new "Holder" with subviews
            holder = new ViewHolder();
            holder.thumbnailImageView = (ImageView) convertView.findViewById(R.id.img_thumbnail);
            holder.titleTextView = (TextView) convertView.findViewById(R.id.text_title);
            holder.authorTextView = (TextView) convertView.findViewById(R.id.text_author);

            // hang onto this holder for future recyclage
            convertView.setTag(holder);
        } else {

            // skip all the expensive inflation/findViewById
            // and just get the holder you already made
            holder = (ViewHolder) convertView.getTag();
        }

        // Get the current book's data in JSON form
        JSONObject jsonObject = (JSONObject) getItem(position);

        // See if there is a cover ID in the Object
        if (jsonObject.has("cover_i")) {

            // If so, grab the Cover ID out from the object
            String imageID = jsonObject.optString("cover_i");

            // Construct the image URL (specific to API)
            String imageURL = IMAGE_URL_BASE + imageID + "-S.jpg";

            // Use Picasso to load the image
            // Temporarily have a placeholder in case it's slow to load
            Picasso.with(mContext).load(imageURL).placeholder(R.drawable.ic_books).into(holder.thumbnailImageView);
        } else {

            // If there is no cover ID in the object, use a placeholder
            holder.thumbnailImageView.setImageResource(R.drawable.ic_books);
        }

        // Grab the title and author from the JSON
        String bookTitle = "";
        String authorName = "";

        if (jsonObject.has("title")) {
            bookTitle = jsonObject.optString("title");
        }

        if (jsonObject.has("author_name")) {
            authorName = jsonObject.optJSONArray("author_name").optString(0);
        }

        // Send these Strings to the TextViews for display
        holder.titleTextView.setText(bookTitle);
        holder.authorTextView.setText(authorName);

        return convertView;
    }

    private static class ViewHolder {
        public ImageView thumbnailImageView;
        public TextView titleTextView;
        public TextView authorTextView;
    }

    public void updateData(JSONArray jsonArray) {
        // update the adapter's dataset
        mJsonArray = jsonArray;
        notifyDataSetChanged();
    }

}

这里是 row_book.xml，列表对象应该是这样的:

<?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="75dp">

    <ImageView
        android:id="@+id/img_thumbnail"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:layout_alignParentLeft="true"
        android:layout_marginLeft="25dp"
        android:layout_centerVertical="true"
        android:scaleType="centerInside"/>

    <TextView
        android:id="@+id/text_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@+id/img_thumbnail"
        android:layout_alignTop="@+id/img_thumbnail"
        android:layout_marginLeft="25dp"/>

    <TextView
        android:id="@+id/text_author"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/text_title"
        android:layout_alignLeft="@+id/text_title"/>

</RelativeLayout>

谢谢。我希望我们能找出列表没有更新的原因。

Answer 1

在 DetailActivity.Java 中你需要像这样声明变量

 TextView myTextView;

然后在onCreate方法里面你需要添加这个

String bookTitle = this.getIntent().getExtras().getString("bookTitle");

仍然在 onCreate 方法中你需要检查是否有有效的 bookTitle

if (bookTitle.length() > 0) {
        myTextView = (TextView) findViewById(R.id.text_title);
        myTextView.setText(String.valueOf(bookTitle));
    }

在 activity_detail.xml 中，您的 xml 文件中唯一缺少的是'android:text="@string/textview"' 在顶部

将其更改为如下所示。请记住，您需要编辑布局位置以适合您的应用。

<TextView
    android:text="@string/textview"
    android:id="@+id/text_title"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="25dp"/>

现在应该会显示书名。按照相同的步骤显示作者姓名。我希望这会有所帮助。