使用从 parse.com 获取的数据清空 RecyclerView答案

【问题标题】：Empty RecyclerView using fetched Data from parse.com使用从 parse.com 获取的数据清空 RecyclerView
【发布时间】：2015-06-12 05:59:55
【问题描述】：

我目前正在努力从我在parse.com 创建的class 中实现数据fetching。我想检索一个名为 "flyerDataFetch" 的对象及其所有元素以显示在 Recyclerview 中。

当我运行和编译程序时，我收到错误：

error:java.lang.NullPointerException at android.view.LayoutInflater.from(LayoutInflater.java:211) 
Error: RecyclerView﹕ No adapter attached; skipping layout.

您能否检查我的代码并帮助确定我在尝试填充我的 RecyclerView 的过程中出错的地方？

MainActivity:

public class HomeScreen extends AppCompatActivity {
    private RecyclerView mRecyclerDrawer;
    private customAdapter mAdapter;
    private Context context;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home_screen);
        setupDrawer();
        final List<Information> data = new ArrayList<>();
        Parse.initialize(this, "xxxxxxxxxxxxxxxxxxxxx", "xxxxxxxxxxxxxxxxxxxxx");
        ParseQuery<ParseObject> query = ParseQuery.getQuery("flyerDataFetch");
        query.getInBackground("xWMyZ4YEGZ", new GetCallback<ParseObject>() {
            @Override
            public void done(ParseObject parseObject, com.parse.ParseException e) {
                if (e == null) {

                    Information information = new Information();
                    information.partyName = parseObject.getString("partyName");
                    information.partyPromoterName = parseObject.getString("partyCost");
                    information.partyCost = parseObject.getString("partyName");

                    information.flyerPic = parseObject.getParseFile("partyFlyerImage");
                    information.partyPromoterPic = parseObject.getParseFile("partyPromoterImage");

                    data.add(information);
                } else {
                    // something went wrong
                }
                mRecyclerDrawer = (RecyclerView) findViewById(R.id.drawerList);
                mRecyclerDrawer.setLayoutManager(new LinearLayoutManager(context));
                mAdapter = new customAdapter(context, data);
                mRecyclerDrawer.setAdapter(mAdapter);
            }
        });

    }

MyApplication:

 @Override
    public void onCreate() {
        super.onCreate();
        sInstance = this;
        ParseCrashReporting.enable(this);
        Parse.enableLocalDatastore(this);
        Parse.initialize(this, "xxxxxxxxxxxxxxxx", "xxxxxxxxxxxxxxxx");
    }

CustomAdapter:

package com.example.jbobo_000.prac;
import android.content.Context;
import android.content.Intent;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import com.parse.ParseImageView;

import java.util.Collections;
import java.util.List;

public class customAdapter extends RecyclerView.Adapter<customAdapter.MyViewHolder> {
    List<Information> data = Collections.emptyList();
    private LayoutInflater inflater;
    private Context context;
    public customAdapter (Context context,List<Information>data){
        this.context=context;
        inflater=LayoutInflater.from(context);
        this.data= data;
    }

   @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType){
       View view= inflater.inflate(R.layout.custom_row, parent, false);
       MyViewHolder holder = new MyViewHolder(view);
       return holder;
   }

    @Override
    public void onBindViewHolder(MyViewHolder holder,int position){
        Information current= data.get(position);
        holder.promoterNameText.setText(current.partyPromoterName);
        holder.costText.setText(current.partyCost);
        holder.partyNameText.setText(current.partyName);
        holder.flyerImage.setParseFile(current.flyerPic);
        holder.promoterImage.setParseFile(current.partyPromoterPic);
    }

    @Override
    public int getItemCount(){

        return data.size();
    }


    class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {
        TextView promoterNameText;
        TextView costText;
        TextView partyNameText;
        ParseImageView flyerImage;
        ParseImageView promoterImage;

        public MyViewHolder(View itemView) {
            super(itemView);
            itemView.setOnClickListener(this);
            promoterImage = (ParseImageView) itemView.findViewById(R.id.promoterPicImage);
            flyerImage = (ParseImageView) itemView.findViewById(R.id.flyertImage);
            costText = (TextView) itemView.findViewById(R.id.costText);
            promoterNameText = (TextView) itemView.findViewById(R.id.promoterNameText);
            partyNameText = (TextView) itemView.findViewById(R.id.partyNameText);
        }

        @Override
        public void onClick(View v) {
            context.startActivity(new Intent(context, partyInformation.class));

        }
    }
}

Information:

package com.example.jbobo_000.prac;
import com.parse.ParseFile;
import com.parse.ParseImageView;

public class Information {
    public ParseFile flyerPic;
    public ParseFile partyPromoterPic;
    public String partyCost;
    public String partyName;
    public String partyPromoterName;



}

Logcat:

06-12 01:52:37.511    5432-5432/com.example.jbobo_000.prac E/RecyclerView﹕ No adapter attached; skipping layout
06-12 01:52:37.766    5432-5432/com.example.jbobo_000.prac D/AndroidRuntime﹕ Shutting down VM
06-12 01:52:37.766    5432-5432/com.example.jbobo_000.prac E/CrashReporting﹕ ParseCrashReporting caught a NullPointerException exception for com.example.jbobo_000.prac. Building report.
06-12 01:52:37.768    5432-5432/com.example.jbobo_000.prac E/CrashReporting﹕ Handling exception for crash
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference
            at android.view.LayoutInflater.from(LayoutInflater.java:219)
            at com.example.jbobo_000.prac.customAdapter.<init>(customAdapter.java:25)
            at com.example.jbobo_000.prac.HomeScreen$1.done(HomeScreen.java:57)
            at com.example.jbobo_000.prac.HomeScreen$1.done(HomeScreen.java:38)
            at com.parse.ParseTaskUtils$2$1.run(ParseTaskUtils.java:107)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5254)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
06-12 01:52:37.768    5432-5432/com.example.jbobo_000.prac D/CrashReporting﹕ Generating report file for crash
06-12 01:52:37.843    5432-5432/com.example.jbobo_000.prac D/CrashReporting﹕ Retrieving logcat output...
06-12 01:52:37.871    5432-5432/com.example.jbobo_000.prac D/CrashReporting﹕ Retrieving logcat output...
06-12 01:52:37.889    5432-5432/com.example.jbobo_000.prac D/CrashReporting﹕ Retrieving logcat output...
06-12 01:52:37.965    5432-5432/com.example.jbobo_000.prac W/Settings﹕ Setting stay_on_always has moved from android.provider.Settings.System to android.provider.Settings.Global, returning read-only value.
06-12 01:52:38.164    5432-5432/com.example.jbobo_000.prac V/CrashReporting﹕ About to start ReportSenderWorker from #handleException
06-12 01:52:38.172    5432-5603/com.example.jbobo_000.prac D/CrashReporting﹕ #checkAndSendReports - start
06-12 01:52:38.172    5432-5603/com.example.jbobo_000.prac D/CrashReporting﹕ Looking for error files in /data/data/com.example.jbobo_000.prac/files/com.parse/cr/reports
06-12 01:52:38.175    5432-5603/com.example.jbobo_000.prac D/CrashReporting﹕ Loading file 1434088357768-NullPointerException-1.stacktrace
06-12 01:52:38.185    5432-5603/com.example.jbobo_000.prac I/CrashReporting﹕ Sending file 1434088357768-NullPointerException-1.stacktrace
06-12 01:52:38.186    5432-5603/com.example.jbobo_000.prac D/CrashReporting﹕ Sending crash report to Parse...
06-12 01:52:38.193    5432-5603/com.example.jbobo_000.prac D/CrashReporting﹕ #checkAndSendReports - finish
06-12 01:52:38.265    5432-5432/com.example.jbobo_000.prac E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.example.jbobo_000.prac, PID: 5432
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.content.Context.getSystemService(java.lang.String)' on a null object reference
            at android.view.LayoutInflater.from(LayoutInflater.java:219)
            at com.example.jbobo_000.prac.customAdapter.<init>(customAdapter.java:25)
            at com.example.jbobo_000.prac.HomeScreen$1.done(HomeScreen.java:57)
            at com.example.jbobo_000.prac.HomeScreen$1.done(HomeScreen.java:38)
            at com.parse.ParseTaskUtils$2$1.run(ParseTaskUtils.java:107)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5254)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
06-12 01:52:38.291    5432-5442/com.example.jbobo_000.prac W/art﹕ Suspending all threads took: 5.494ms

【问题讨论】：

标签： java android json parse-platform android-recyclerview

【解决方案1】：

这是您应该更改的所有内容.. 首先您没有获得表（对象）flyerDataFetch 的所有数据，您只是获得了一个特定的列数据，其 id 为“xWMyZ4YEGZ”，您的查询应该是

ParseQuery<ParseObject> query = ParseQuery.getQuery("flyerDataFetch");
    query.findInBackgroud(new FindCallBack<TableClass>(){


        @Override
        public void done(ParseObject List<TableName> list, com.parse.ParseException e) {
            if (e == null) {

       // GENERATE LOOP HERE AND GET ALL DATA OF LIST INTO YOUR LOCAL LIST WHICH YOU ARE PASSING TO ADAPTER OF RECYCLER VIEW
      //I am telling you to add loop so you can learn.. 
                Information information = new Information();
                information.partyName = parseObject.getString("partyName");
                information.partyPromoterName = parseObject.getString("partyCost");
                information.partyCost = parseObject.getString("partyName");

                information.flyerPic = parseObject.getParseFile("partyFlyerImage");
                information.partyPromoterPic = parseObject.getParseFile("partyPromoterImage");

                data.add(information);
            } else {
                // something went wrong
            }

这将从表中获取所有数据并设置在您传递给适配器的列表中。这可能是您的 NullPointerException 的原因！

另一件事是您获取图像的方式是错误的您实际上需要执行查询并获取 bytes[] 数组，然后您可以在 ParseImageView 中进行设置

Bitmap bmp = BitmapFactory.decodeByteArray(data, 0, data.length, options);
myViewHolder.myImageView.setBitmapImage(bmp);

您的 customAdapter 中也不需要上下文 .. 只需这样写

private LayoutInflater inflater;

public customAdapter (Context context,List<Information>data){
    inflater=LayoutInflater.from(context);
    this.data= data;
}

也在你的 MainActivity 类中..改变这个

 mRecyclerDrawer.setLayoutManager(new LinearLayoutManager(context));
mAdapter = new customAdapter(context, data);

到

  mRecyclerDrawer.setLayoutManager(new LinearLayoutManager(this));
mAdapter = new customAdapter(getApplicationContext(), data);

.. 声明您的以下数据

final List<Information> data = new ArrayList<>();

在你的 MainActivity onCreate() 方法之前..

希望对你有帮助！

【讨论】：

非常感谢您的反馈！我会执行你的更正！
我更新了..进行更改..现在要正确获取文本只需实施必要的更改，您可以稍后查询图像..如果仍然有任何问题，请告诉我..
我想通了，现在 recyclerview 中填充了您的帮助。谢谢！你介意详细介绍我如何填充我的两个图像视图吗？
我已经给了你在 imagequery 中需要做的最重要的事情。n 然后放入 myViewHolder .. 只需要从 parse in bytes[] 中获取数据，然后像我一样将其转换为位图在回答中告诉你...

【解决方案2】：

context 为空。请在调用适配器之前为活动设置上下文值。添加

setContentView(R.layout.activity_home_screen);
context=this;

【讨论】：