java - Loader onCreateLoader 不返回 String

Question

我想解析对普通 String 的 JSON 响应，但是当我尝试返回 jsonString 时，我收到以下消息:

Incompatible types:
Required:
android.content.Loader
<java.lang.String>
Found:
java.lang.String

你能向我解释一下我做错了什么吗？

package com.example.entropy.booklist;

import android.app.LoaderManager;
import android.content.Loader;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.widget.ListView;

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.URL;
import java.util.ArrayList;

import static android.R.attr.data;

/**
 * Created by entropy on 18/07/17.
 */

public class AllInOne extends AppCompatActivity implements LoaderManager.LoaderCallbacks<String> {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.all_in_one);
        getLoaderManager().initLoader(0, null, this);

    }

    String jsonStr ;

    @Override
    public Loader<String> onCreateLoader(int id, Bundle args) {
        HttpURLConnection urlConnection = null;
        BufferedReader reader = null;

        String line;
        try {
            URL url = new URL("https://earthquake.usgs.gov/fdsnws/event/1/query?format=geojson&starttime=2012-01-01&endtime=2012-12-01&minmagnitude=6");
            urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("GET");
            urlConnection.connect();
            InputStream inputStream = urlConnection.getInputStream();
            StringBuffer buffer = new StringBuffer();
            if (inputStream == null)
            {return null;}

            reader = new BufferedReader(new InputStreamReader(inputStream));
            while ((line = reader.readLine()) != null) buffer.append(line);
           if (buffer.length() == 0)
            {return null;}

            jsonStr = buffer.toString();



        } catch (IOException e) {
            return null;

        } finally {
            if (urlConnection != null) urlConnection.disconnect();
            if (reader != null) {
                try {
                    reader.close();

                } catch (final IOException e) {
                    Log.e("MainActivity", "Error closing stream", e);
                }
            }
        }
        return jsonStr;
    }

Answer 1

首先，您的错误消息绝对正确“不兼容的类型:必需:android.content.Loader 找到:java.lang.String”，因为您正在返回 String但方法想要 Loader<String> .

其次，您使用加载器的方式是错误的。数据加载不应该在 onCreateLoader() 。检查此链接以获取正确的信息，在继续任何实现之前阅读此文档。 https://developer.android.com/guide/components/loaders.html

另外，请查看AsyncTaskLoader在同一个文档中。这将实现您从服务器加载数据的目的。