viewpager+fragment联网加载数据无显示以及预加载问题解决

           最近用fragment+viewpager来做多页面联网加载数据的功能，本来也觉得没什么，可是就是有很多问题，比如页面切换后就没有数据显示了，预加载数据很费流量问题，所以在这里记录一下，以后省的每次都去解决这种问题了。贴出所有代码，方法是按照fragment的生命周期写的。(url就自己写吧)

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ProgressBar;

import com.google.gson.Gson;
import com.hawk.android.hicamera.adapter.MaterialAdapter;
import com.hawk.android.hicamera.bean.Data;
import com.zhy.http.okhttp.OkHttpUtils;
import com.zhy.http.okhttp.callback.StringCallback;

import okhttp3.Call;

/**
 * Created by lenovo on 2016/11/7.
 */

public class MaterialFragment extends Fragment {
    private static final String url = "";
    private RecyclerView mRecyclerView;
    private Data mData;//联网得到的数据
    private MaterialAdapter mMaterialAdapter;
    private String mTitle;
    private ProgressBar mProgressBar;

    public static MaterialFragment getInstance(String title) {
        MaterialFragment materialFragment = new MaterialFragment();
        Bundle bundle = new Bundle();
        bundle.putString("title", title);
        materialFragment.setArguments(bundle);
        return materialFragment;
    }

    @Override
    public void setUserVisibleHint(boolean isVisibleToUser) {
        super.setUserVisibleHint(isVisibleToUser);
        if (isVisibleToUser && isVisible()) {//视图可见并且控件准备好了，每次都会调用
            if (null == mData) {//如果数据为空了，则需要重新联网请求
                loadDataFromNet();
            }
        }
    }

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mTitle = getArguments().getString("title");
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_material, container, false);
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        mProgressBar = (ProgressBar) view.findViewById(R.id.pb_material);
        mRecyclerView = (RecyclerView) view.findViewById(R.id.rv_material);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this.getContext(), LinearLayoutManager.VERTICAL, false));
        mRecyclerView.setHasFixedSize(true);
        mMaterialAdapter = new MaterialAdapter(this);
        mRecyclerView.setAdapter(mMaterialAdapter);
        if (null == mData && getUserVisibleHint()) {
            loadDataFromNet();//解决第一个fragment无法加载数据问题
        }
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        if (null != mData && null != mMaterialAdapter) {//解决切换后闪屏已经无数据显示问题
            mMaterialAdapter.notifyData(mData.data.filmRecommends);
        }
    }

    @Override
    public void onResume() {
        super.onResume();
    }

    @Override
    public void onPause() {
        super.onPause();
        OkHttpUtils.getInstance().cancelTag(this);
        mProgressBar.setVisibility(View.GONE);
    }

    /**
     * 加载数据
     */
    private void loadDataFromNet() {
        mProgressBar.setVisibility(View.VISIBLE);
        OkHttpUtils
                .get()
                .url(url)
                .tag(this)
                .addParams("deviceId", "b0e8cc2f-6098-3596-b580-d76f30850f69")
                .addParams("appToken", "6558E6B7CB1741BDC79A93FB1C9B629DB18B4D434824B99729783976ECB42C6A573AD5F1F73DEF0383F968C8EACA2096")
                .build()
                .execute(new StringCallback() {
                    @Override
                    public void onError(Call call, Exception e, int id) {

                    }

                    @Override
                    public void onResponse(String response, int id) {
                        Gson gson = new Gson();
                        mData = gson.fromJson(response, Data.class);
                        if (null != mData) {
                            mMaterialAdapter.notifyData(mData.data.filmRecommends);
                            mProgressBar.setVisibility(View.GONE);
                        }
                    }
                });
    }
}

xml文件如下

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/rv_material"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@android:color/white"/>

    <ProgressBar
        android:id="@+id/pb_material"
        android:visibility="gone"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        />
</FrameLayout>

对了，viewpager的adaper也贴出来吧；

public class MaterialStoreAdapter extends FragmentPagerAdapter {
    private ArrayList<MaterialFragment> mFragments;

    public MaterialStoreAdapter(FragmentManager fm, ArrayList<MaterialFragment> fragments) {
        super(fm);
        this.mFragments = fragments;
    }

    @Override
    public Fragment getItem(int position) {
        return mFragments.get(position);
    }

    @Override
    public int getCount() {
        return mFragments == null ? 0 : mFragments.size();
    }
}

下次再遇到这个问题，直接过来复制粘贴就ok了。。。

参考文章地址：http://www.cnblogs.com/wangfeng520/p/5807465.html