Question

我正在尝试将上下文传递给自定义Loader，但我得到的类型不匹配。在onCreateLoader return new NewsLoader(CONTEXT, url);我尝试使用getActivity()和getContext()以及getApplicationContext()方法作为输入。

错误;

getContext()“必需的android.support.v4.loader <java.util.arraylist<com.example.android.greennewswire.News>

NewsLoader中的

this NewsLoader（android.content.Context，String）无法应用于（com.example.android.greennewswire.NewsFragmentBBC，String）

`package com.example.android.greennewswire;

import android.content.Context;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.LoaderManager;
import android.support.v4.content.Loader;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import java.util.ArrayList;


public class NewsFragmentBBC extends Fragment implements LoaderManager.LoaderCallbacks<ArrayList<News>>{

    //String object holding the network request URL to be passed into the Loader
    private static final String NEWS_REQUEST_URL = "https://www.googleapis.com/books/v1/volumes?q=android";

    public NewsFragmentBBC() {
        // Required empty public constructor
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.list, container, false);

        //Create a LoaderManager and initialise the Loader
        LoaderManager loaderManager = getLoaderManager();
        loaderManager.initLoader(1, null, this);




        return rootView;
    }

    @Override
    public Loader<ArrayList<News>> onCreateLoader(int id, Bundle args) {
        return new NewsLoader(this, NEWS_REQUEST_URL);
    }

    @Override
    public void onLoadFinished(Loader<ArrayList<News>> loader, ArrayList<News> data) {

    }

    @Override
    public void onLoaderReset(Loader<ArrayList<News>> loader) {

        }
  }

NewsLoader类

package com.example.android.greennewswire;

import android.content.AsyncTaskLoader;
import android.content.Context;

import java.util.ArrayList;



public class NewsLoader extends AsyncTaskLoader<ArrayList<News>> {

    private String mUrl;

    //Default constructor to take input objects
    public NewsLoader (Context context, String url) {
        super(context);
        mUrl = url;
    }

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

    @Override
    public ArrayList<News> loadInBackground() {
        //Null check
        if (mUrl == null) {
            return null;
        }
        ArrayList<News> news = QueryUtils.fetchNewsData(mUrl);
        return news;
    }
}

Answer 1

我通过将LoaderManager的导入库从android.support.v4.app.LoaderManager更改为android.app.LoaderManager并确保实现的回调与该库匹配来解决此问题。然后我能够在我的getContext()参数中使用NewsLoader方法而没有问题。

Fragment类中的Loader上下文

1 个答案: