AsyncTaskLoader Example

MainActivity.java

/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.example.android.asynctaskloader;

import android.os.Bundle;
import android.support.v4.app.LoaderManager;
import android.support.v4.content.AsyncTaskLoader;
import android.support.v4.content.Loader;
import android.support.v7.app.AppCompatActivity;
import android.text.TextUtils;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;

import com.example.android.asynctaskloader.utilities.NetworkUtils;

import java.io.IOException;
import java.net.URL;

import static android.text.TextUtils.isEmpty;

public class MainActivity extends AppCompatActivity implements LoaderManager.LoaderCallbacks<String>{

    private static final String TAG = MainActivity.class.getSimpleName();

    /* A constant to save and restore the URL that is being displayed */
    private static final String SEARCH_QUERY_URL_EXTRA = "query";

    public static final int GITHUB_SEARCH_LOADER = 22;

    private EditText mSearchBoxEditText;

    private TextView mUrlDisplayTextView;
    private TextView mSearchResultsTextView;

    private TextView mErrorMessageDisplay;

    private ProgressBar mLoadingIndicator;

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

        mSearchBoxEditText = (EditText) findViewById(R.id.et_search_box);
        mUrlDisplayTextView = (TextView) findViewById(R.id.tv_url_display);
        mSearchResultsTextView = (TextView) findViewById(R.id.tv_github_search_results_json);
        mErrorMessageDisplay = (TextView) findViewById(R.id.tv_error_message_display);
        mLoadingIndicator = (ProgressBar) findViewById(R.id.pb_loading_indicator);
        if (savedInstanceState != null) {
            String queryUrl = savedInstanceState.getString(SEARCH_QUERY_URL_EXTRA);
            mUrlDisplayTextView.setText(queryUrl);
        }
        getSupportLoaderManager().initLoader(GITHUB_SEARCH_LOADER, null, this);
    }

    /**
     * This method retrieves the search text from the EditText, constructs the
     * URL (using {@link NetworkUtils}) for the github repository you'd like to find, displays
     * that URL in a TextView, and finally request that an AsyncTaskLoader performs the GET request.
     */
    private void makeGithubSearchQuery() {
        String githubQuery = mSearchBoxEditText.getText().toString();
        if (githubQuery==null || TextUtils.isEmpty(githubQuery)) {
            mUrlDisplayTextView.setText(R.string.error_nothing);
        } else {
            URL githubSearchUrl = NetworkUtils.buildUrl(githubQuery);
            mUrlDisplayTextView.setText(githubSearchUrl.toString());
            Bundle bundle = new Bundle();
            bundle.putString(SEARCH_QUERY_URL_EXTRA, githubSearchUrl.toString());
            LoaderManager loaderManager = getSupportLoaderManager();
            Loader<String> githubSearchLoader = loaderManager.getLoader(GITHUB_SEARCH_LOADER);
            if (githubSearchLoader==null) {
                loaderManager.initLoader(GITHUB_SEARCH_LOADER, bundle, this);
            } else {
                loaderManager.restartLoader(GITHUB_SEARCH_LOADER, bundle, this);
            }
        }
    }

    /**
     * This method will make the View for the JSON data visible and
     * hide the error message.
     * <p>
     * Since it is okay to redundantly set the visibility of a View, we don't
     * need to check whether each view is currently visible or invisible.
     */
    private void showJsonDataView() {
        /* First, make sure the error is invisible */
        mErrorMessageDisplay.setVisibility(View.INVISIBLE);
        /* Then, make sure the JSON data is visible */
        mSearchResultsTextView.setVisibility(View.VISIBLE);
    }

    /**
     * This method will make the error message visible and hide the JSON
     * View.
     * <p>
     * Since it is okay to redundantly set the visibility of a View, we don't
     * need to check whether each view is currently visible or invisible.
     */
    private void showErrorMessage() {
        /* First, hide the currently visible data */
        mSearchResultsTextView.setVisibility(View.INVISIBLE);
        /* Then, show the error */
        mErrorMessageDisplay.setVisibility(View.VISIBLE);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int itemThatWasClickedId = item.getItemId();
        if (itemThatWasClickedId == R.id.action_search) {
            makeGithubSearchQuery();
            return true;
        }
        return super.onOptionsItemSelected(item);
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        String queryUrl = mUrlDisplayTextView.getText().toString();
        outState.putString(SEARCH_QUERY_URL_EXTRA, queryUrl);
    }

    @Override
    public Loader<String> onCreateLoader(int id, final Bundle args) {
        return new AsyncTaskLoader<String>(this) {
            String mCache;
            @Override
            protected void onStartLoading() {
                if (args!=null) {
                    if (mCache==null) {
                        mLoadingIndicator.setVisibility(View.VISIBLE);
                        forceLoad();
                    } else {
                        deliverResult(mCache);
                    }
                }
            }

            @Override
            public String loadInBackground() {
                String urlStr = args.getString(SEARCH_QUERY_URL_EXTRA);
                if (urlStr==null || isEmpty(urlStr)) {
                    return null;
                } else {
                    String githubSearchResults = null;
                    try {
                        githubSearchResults = NetworkUtils.getResponseFromHttpUrl(new URL(urlStr));
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                    return githubSearchResults;
                }
            }
            @Override
            public void deliverResult(String githubJson) {
                mGithubJson = githubJson;
                super.deliverResult(githubJson);
            }
        };
    }

    @Override
    public void onLoadFinished(Loader<String> loader, String githubSearchResults) {
        mLoadingIndicator.setVisibility(View.INVISIBLE);
        if (githubSearchResults != null && !githubSearchResults.equals("")) {
            showJsonDataView();
            mSearchResultsTextView.setText(githubSearchResults);
        } else {
            showErrorMessage();
        }
    }

    @Override
    public void onLoaderReset(Loader<String> loader) { }
}

gives error