Question

我创建了一个应用程序，根据用户输入的查询关键字显示10本书的列表。

我使用EditText视图供用户输入查询。

我还使用ImageButton作为搜索按钮。

我使用了一个自定义类，其范围AsyncTaskLoader可以将内容加载到我的ListView。

我已经从应用的MainActivity调用了initloader()方法，并从OnCreateLoader覆盖方法调用了我的自定义加载器。

我希望加载程序仅在按钮单击时获取数据，而不是在活动开始时自动获取数据。

主要活动

package com.example.shara.booklistapp;

import android.app.LoaderManager;
import android.content.Context;
import android.content.Intent;
import android.content.Loader;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.net.Uri;
import android.provider.ContactsContract;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.ProgressBar;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

import static android.app.LoaderManager.*;
import static com.example.shara.booklistapp.BookQueryUtils.LOG_TAG;

public class MainActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<List<Blist>> {
    private ListAdapter mAdapter;
    private static final int BOOK_LOADER_ID = 1;
    private String Book_list_request_url = "Michael Jackson";
    private ProgressBar progressBar;
    private NetworkInfo networkInfo;
    private TextView emptytextview;
    private EditText editText;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ListView booklistview = findViewById(R.id.list);
        progressBar = findViewById(R.id.progressbar);
        mAdapter = new ListAdapter(this, new ArrayList<Blist>());
        booklistview.setAdapter(mAdapter);
        ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        networkInfo = connectivityManager.getActiveNetworkInfo();
        emptytextview = (TextView) findViewById(R.id.emptytextview);
        editText = findViewById(R.id.search_query_text_view);
        booklistview.setEmptyView(emptytextview);
        booklistview.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Blist currentBook = mAdapter.getItem(position);
                Uri currentbookk = Uri.parse(currentBook.getUrl());

                startActivity(new Intent(Intent.ACTION_VIEW, currentbookk));
            }
        });

        LoaderManager loaderManager = getLoaderManager();
        loaderManager.initLoader(BOOK_LOADER_ID, null, this);
    }

    //Overriding the abstract methods of the Loadermanager
    @Override
    public Loader<List<Blist>> onCreateLoader(int id, Bundle bundle) {
        Log.i(LOG_TAG, Book_list_request_url);
        return new BlistLoader(this, Book_list_request_url);
    }

    @Override
    public void onLoadFinished(Loader<List<Blist>> loader, List<Blist> blists) {

        progressBar.setVisibility(View.GONE);

        //Using the networkInfo variable declared earlier to check whether the system has internet connectivity and displays a message if there isn't one.
        if (networkInfo == null) {
            emptytextview.setText(R.string.no_network);
        } else {
            emptytextview.setVisibility(View.GONE);
        }

        mAdapter.clear();
        if (blists != null && !blists.isEmpty()) {
            mAdapter.addAll(blists);

        }
    }

    @Override
    public void onLoaderReset(Loader loader) {
        Log.i(LOG_TAG, "Testing: onLoaderReset is successfully called");
        mAdapter.clear();
    }
}

Custom Loader类

package com.example.shara.booklistapp;

import android.content.AsyncTaskLoader;
import android.content.Context;
import android.util.Log;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.ImageButton;

import org.json.JSONException;

import java.io.IOException;
import java.util.List;

public class BlistLoader extends AsyncTaskLoader<List<Blist>> {
    private static final String LOG_TAG = BaseAdapter.class.getName();
    private String mUrl;

    public BlistLoader(Context context, String url) {
        super(context);

        mUrl = url;
    }

    @Override
    protected void onStartLoading() {
        Log.i(LOG_TAG, "Testing: onStartLoading is successfully called");
        forceLoad();
    }

    @Override
    public List<Blist> loadInBackground() {

        Log.i(LOG_TAG, "Testing: loadInBackground is successfully called");
        if (mUrl == null) {
            return null;
        }
        List<Blist> blists = null;
        try {
            blists = BookQueryUtils.fetchBookList(mUrl);
        } catch (IOException e) {
            e.printStackTrace();
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return blists;
    }
}

包含ImageButton的XML

<?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:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:orientation="horizontal">

        <EditText
            android:id="@+id/search_query_text_view"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="2"
            android:hint="@string/hint" />

        <ImageButton
            android:id="@+id/search_button1"
            android:layout_width="42dp"
            android:layout_height="42dp"
            android:src="@drawable/search" />

    </LinearLayout>

    <TextView
        android:id="@+id/result"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginLeft="10dp"
        android:backgroundTint="@color/colorPrimaryDark"
        android:backgroundTintMode="add"
        android:text="Results" />

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <ListView
            android:id="@+id/list"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_margin="10dp"
            android:dividerHeight="1dp" />

        <ProgressBar
            android:id="@+id/progressbar"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerInParent="true" />

        <TextView
            android:id="@+id/emptytextview"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerInParent="true"
            android:text="" />
    </RelativeLayout>

</LinearLayout>

我希望oncreateloader方法仅在单击搜索按钮时执行，否则不执行。

如何实现这一目标？我的代码是否需要大量修改，或者只是我完全错过的内容。

我之前曾问同样的问题here，但我没有得到任何答案。任何帮助将不胜感激。

Book query utils用于HTTP请求和JSON解析。

package com.example.shara.booklistapp;

import android.net.Uri;
import android.text.TextUtils;
import android.util.Log;
import android.view.View;
import android.widget.Button;

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.nio.charset.Charset;
import java.util.ArrayList;
import java.util.List;

/**
 * Created by shara on 12/17/2017.
 */

public final class BookQueryUtils {

    public static final String LOG_TAG = BookQueryUtils.class.getName();

    private BookQueryUtils() {

    }

    private static URL createURL(String search_query) throws MalformedURLException {
        URL url = null;
        String q = "q";
        try {
            final String base_URL = "https://www.googleapis.com/books/v1/volumes?";
            Uri final_Url = Uri.parse(base_URL).buildUpon()
                    .appendQueryParameter(q, search_query)
                    .build();
            url = new URL(final_Url.toString());
            Log.i(LOG_TAG, "The final Url is" + url);
        } catch (MalformedURLException e) {
            Log.e(LOG_TAG, "Url could not be formed", e);
        }
        return url;
    }

    private static String theHTTPRequest(URL url) throws IOException {
        String jsonResponse = "";
        if (url == null) {
            return jsonResponse;
        }
        HttpURLConnection connectionUrl = null;
        InputStream theInputStream = null;

        try {
            connectionUrl = (HttpURLConnection) url.openConnection();
            connectionUrl.setReadTimeout(10000);
            connectionUrl.setConnectTimeout(15000);
            connectionUrl.setRequestMethod("GET");
            connectionUrl.connect();
            if (connectionUrl.getResponseCode() == 200) {
                theInputStream = connectionUrl.getInputStream();
                jsonResponse = readFromStream(theInputStream);
            } else {
                Log.e(LOG_TAG, "could not make the connection");
            }
        } catch (IOException e) {
            Log.e(LOG_TAG, "Problem getting the requested data", e);
        } finally {
            if (connectionUrl != null) {
                connectionUrl.disconnect();
            }
            if (theInputStream != null) {
                theInputStream.close();
            }
        }
        return jsonResponse;
    }

    private static String readFromStream(InputStream inputStream) throws IOException {
        StringBuilder streamoutput = new StringBuilder();
        InputStreamReader inputStreamReader = new InputStreamReader(inputStream, Charset.forName("UTF-8"));
        BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
        String urlline = bufferedReader.readLine();
        while (urlline != null) {
            streamoutput.append(urlline);
            urlline = bufferedReader.readLine();
        }
        return streamoutput.toString();
    }

    private static List<Blist> extractFeatureFromJSON(String BlistJSON) throws JSONException {
        if (TextUtils.isEmpty(BlistJSON)) {
            return null;
        }

        List<Blist> blists = new ArrayList<>();
        try {
            String a = "";
            JSONObject baseJSON = new JSONObject(BlistJSON);
            JSONArray items = baseJSON.getJSONArray("items");
            for (int i = 0; i < items.length(); i++) {
                Blist blistss = new Blist();
                JSONObject j = items.getJSONObject(i);
                JSONObject vInfo = j.getJSONObject("volumeInfo");
                if (vInfo.has("authors")) {
                    JSONArray athrs = vInfo.getJSONArray("authors");
                    if (athrs.length() != 0) {
                        for (int k = 0; k < athrs.length(); k++) {
                            a = athrs.getString(k);
                            blistss.setAuthor(a);
                        }
                    }
                }
                if (vInfo.has("imageLinks")) {
                    JSONObject thumbnail = vInfo.getJSONObject("imageLinks");
                    blistss.setImage(thumbnail.getString("thumbnail"));
                }
                blistss.setUrl(vInfo.getString("previewLink"));
                blistss.setTitle(vInfo.getString("title"));
                blistss.setPublisher(vInfo.getString("publisher"));
                blists.add(blistss);
            }
        } catch (JSONException e) {
            Log.e(LOG_TAG, "Could not parse JSON", e);
        }
        return blists;
    }

    public static List<Blist> fetchBookList(String query_url) throws IOException, JSONException {
        URL url = createURL(query_url);
        String JSONResponse = null;
        try {
            JSONResponse = theHTTPRequest(url);
        } catch (IOException e) {
            Log.e(LOG_TAG, "Could not fetch data");
        }
        List<Blist> blists = extractFeatureFromJSON(JSONResponse);
        return blists;
    }
}

这是我对listview的适配器。

package com.example.shara.booklistapp;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.provider.ContactsContract;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.ProgressBar;
import android.widget.SearchView;
import android.widget.TextView;

import java.io.InputStream;
import java.util.ArrayList;

/**
 * Created by shara on 12/17/2017.
 */

public class ListAdapter extends ArrayAdapter<Blist> {
    private ProgressBar progressBar;

    public ListAdapter(@NonNull Context context, ArrayList<Blist> blists) {
        super(context, 0, blists);
    }

    public String rslt;

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        View listitemview = convertView;
        if (listitemview == null) {
            listitemview = LayoutInflater.from(getContext()).inflate(R.layout.list_layout, parent, false);
        }
        Blist blist = getItem(position);

        ImageView thumbnail = listitemview.findViewById(R.id.thumbnail_imageview);
        new imageLoader(thumbnail).execute(blist.getImage());
        progressBar = listitemview.findViewById(R.id.Image_Progress_bar);
        progressBar.setVisibility(View.GONE);
        TextView title = listitemview.findViewById(R.id.title_textview);
        title.setText(blist.gettitle());

        TextView author = listitemview.findViewById(R.id.author_textview);
        author.setText(blist.getauthor());
        TextView publisher = listitemview.findViewById(R.id.publisher_texview);
        publisher.setText(blist.getpublisher());

        return listitemview;
    }

    private class imageLoader extends AsyncTask<String, Void, Bitmap> {
        ImageView bmImage;

        public imageLoader(ImageView bmImage) {
            this.bmImage = bmImage;
        }

        protected Bitmap doInBackground(String... urls) {
            String urldisplay = urls[0];
            Bitmap mIcon11 = null;
            try {
                InputStream in = new java.net.URL(urldisplay).openStream();
                mIcon11 = BitmapFactory.decodeStream(in);
            } catch (Exception e) {
                Log.e("Error", e.getMessage());
                e.printStackTrace();
            }
            return mIcon11;
        }

        protected void onPostExecute(Bitmap result) {

            bmImage.setImageBitmap(result);

        }
    }
}

Answer 1

已在代码中更新

最初设置空查询

private String Book_list_request_url = "";

为＆＃34;搜索点击（图片按钮）＆＃34;

创建方法

public void Search(View v)
{
    Book_list_request_url = editText.getText().toString();
    loaderManager.restartLoader(BOOK_LOADER_ID, null, this);
}

向图像按钮添加方法

  <ImageButton
        android:id="@+id/search_button1"
        android:layout_width="42dp"
        android:layout_height="match_parent"
        android:onClick="Search"
        android:src="@drawable/ic_launcher_background" />

使用按钮单击控制AsynTaskLoader

1 个答案: