在自定义列表的文本视图中设置数据时出现 NullPointerException [重复]答案

【问题标题】：NullPointerException when setting data in textview in a custom list [duplicate]在自定义列表的文本视图中设置数据时出现 NullPointerException [重复]
【发布时间】：2017-02-10 10:14:42
【问题描述】：

我正在尝试创建一个自定义列表来显示来自 arraylist 的数据，但它在这一行中给了我一个 NullPointerException：

tvtitle.setText(all.get(position).getTitle());

all 是数组列表，其对象包含字段 Title

这是将自定义列表类作为内部类的活动

package com.heshamkadry.social.app;

import android.app.ProgressDialog;
import android.content.Context;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.TextView;

import com.heshamkadry.social.Api.OnTaskCompleteTodo;
import com.heshamkadry.social.Api.TodoAPI;
import com.heshamkadry.social.R;
import com.heshamkadry.social.Users.ToDo;

import java.util.ArrayList;

public class TodoView extends AppCompatActivity implements OnTaskCompleteTodo {
TodoAPI todoAPI;
ListView lsview;
ArrayList<ToDo> all;
String id;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_todo_view);
    ProgressDialog progressDialog = new ProgressDialog(this);
    lsview = (ListView) findViewById(R.id.ActivityTodoView_ListView_Todo);
    todoAPI = new TodoAPI(this , progressDialog);
    id = getIntent().getStringExtra("id");
    todoAPI.execute("?userId="+id);
}

@Override
public void OnCompleteListner() {
    try
    {
        all=todoAPI.get();
        CustomAdapter myarrayadapter = new CustomAdapter(this , android.R.layout.simple_list_item_1 , all);
        lsview.setAdapter(myarrayadapter);
    }catch (Exception x){
        x.printStackTrace();
    }

}

public class CustomAdapter extends ArrayAdapter
{
    public LayoutInflater inflator;

    CustomAdapter(Context context , int resourses , ArrayList objects){
        super(context,resourses,objects);
    }

    @NonNull
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        if(inflator == null){
            inflator = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        }if(convertView == null){
            convertView = inflator.inflate(R.layout.listt_item ,null);
        }

        TextView tvtitle = (TextView) convertView.findViewById(R.id.ListItem_TextView_title);
        TextView tvcoler = (TextView) convertView.findViewById(R.id.ListItem_TextView_coloer);

        tvtitle.setText(all.get(position).getTitle());

        if(all.get(position).isCompleted()){
            tvcoler.setBackgroundColor(0xFF00CC00);
        }else{
            tvcoler.setBackgroundColor(0xFF00CCCC);
        }
        return convertView;
    }
}
}

这里是自定义列表xml

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

<TextView
    android:text="TextView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_alignParentStart="true"
    android:layout_marginStart="15dp"
    android:layout_marginTop="19dp"
    android:id="@+id/ListItem_TextView_title" />

<TextView
    android:text="TextView"
    android:layout_width="30dp"
    android:layout_height="30dp"
    android:layout_alignBottom="@+id/ListItem_TextView_title"
    android:layout_alignParentEnd="true"
    android:layout_marginEnd="14dp"
    android:id="@+id/ListItem_TextView_coloer"
    android:background="@color/colorAccent" />
</RelativeLayout>

这里是例外

02-11 12:06:59.356 30758-30758/com.heshamkadry.social E/AndroidRuntime: FATAL EXCEPTION: main
                                                                        java.lang.NullPointerException
                                                                            at com.heshamkadry.social.app.TodoView$CustomAdapter.getView(TodoView.java:72)
                                                                            at android.widget.AbsListView.obtainView(AbsListView.java:2181)
                                                                            at android.widget.ListView.makeAndAddView(ListView.java:1880)
                                                                            at android.widget.ListView.fillDown(ListView.java:687)
                                                                            at android.widget.ListView.fillDown(ListView.java:666)
                                                                            at android.widget.ListView.fillFromTop(ListView.java:758)
                                                                            at android.widget.ListView.layoutChildren(ListView.java:1695)
                                                                            at android.widget.AbsListView.onLayout(AbsListView.java:2016)
                                                                            at android.view.View.layout(View.java:14471)
                                                                            at android.view.ViewGroup.layout(ViewGroup.java:4562)
                                                                            at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1076)
                                                                            at android.view.View.layout(View.java:14471)
                                                                            at android.view.ViewGroup.layout(ViewGroup.java:4562)
                                                                            at android.widget.FrameLayout.onLayout(FrameLayout.java:452)
                                                                            at android.view.View.layout(View.java:14471)
                                                                            at android.view.ViewGroup.layout(ViewGroup.java:4562)
                                                                            at android.support.v7.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:437)
                                                                            at android.view.View.layout(View.java:14471)
                                                                            at android.view.ViewGroup.layout(ViewGroup.java:4562)
                                                                            at android.widget.FrameLayout.onLayout(FrameLayout.java:452)
                                                                            at android.view.View.layout(View.java:14471)
                                                                            at android.view.ViewGroup.layout(ViewGroup.java:4562)
                                                                            at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1671)
                                                                            at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1525)
                                                                            at android.widget.LinearLayout.onLayout(LinearLayout.java:1434)
                                                                            at android.view.View.layout(View.java:14471)
                                                                            at android.view.ViewGroup.layout(ViewGroup.java:4562)
                                                                            at android.widget.FrameLayout.onLayout(FrameLayout.java:452)
                                                                            at android.view.View.layout(View.java:14471)
                                                                            at android.view.ViewGroup.layout(ViewGroup.java:4562)
                                                                            at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:1986)
                                                                            at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1740)
                                                                            at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1009)
                                                                            at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5508)
                                                                            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:749)
                                                                            at android.view.Choreographer.doCallbacks(Choreographer.java:562)
                                                                            at android.view.Choreographer.doFrame(Choreographer.java:532)
                                                                            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:735)
                                                                            at android.os.Handler.handleCallback(Handler.java:730)
                                                                            at android.os.Handler.dispatchMessage(Handler.java:92)
                                                                            at android.os.Looper.loop(Looper.java:213)
                                                                            at android.app.ActivityThread.main(ActivityThread.java:5225)
                                                                            at java.lang.reflect.Method.invokeNative(Native Method)
                                                                            at java.lang.reflect.Method.invoke(Method.java:525)
                                                                            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:741)
                                                                            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
                                                                            at dalvik.system.NativeStart.main(Native Method)

简单的列表视图运行没有问题

编辑

这里是待办事项异步任务

package com.heshamkadry.social.Api;

import android.app.ProgressDialog;
import android.os.AsyncTask;
import android.util.Base64;

import com.heshamkadry.social.Users.ToDo;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;
import org.json.JSONArray;
import org.json.JSONObject;

import java.util.ArrayList;

/**
 * Created by Hesham Kadry on 2/10/2017.
 */

public class TodoAPI extends AsyncTask<String , String ,ArrayList<ToDo>> {
    ProgressDialog progressDialog;
    OnTaskCompleteTodo onTaskCompleteTodo;

    public TodoAPI(OnTaskCompleteTodo onTaskCompleteTodo , ProgressDialog progressDialog){
        this.progressDialog = progressDialog;
        this.onTaskCompleteTodo = onTaskCompleteTodo;
    }

    @Override
    protected void onPreExecute() {
        progressDialog.setMessage("loading......");
        progressDialog.setCancelable(false);
        progressDialog.show();
    }

    @Override
    protected ArrayList<ToDo> doInBackground(String... strings)
    {
        ArrayList<ToDo> alltodo = new ArrayList<ToDo>();

        try
        {
            HttpClient client = new DefaultHttpClient();
            HttpGet request = new HttpGet("http://jsonplaceholder.typicode.com/todos"+strings[0]);
            String authorizationString = "Basic " + Base64.encodeToString(
                    ("tester" + ":" + "tm-sdktest").getBytes(),
                    Base64.NO_WRAP);

            request.setHeader("Authorization", authorizationString);
            HttpResponse response = client.execute(request);

            HttpEntity entity = response.getEntity();

            String result = EntityUtils.toString(entity);
            int statuescode = response.getStatusLine().getStatusCode();

            if(statuescode == 200)
            {
                JSONArray jsonArray = new JSONArray(result);

                for (int counter=0 ; counter<jsonArray.length() ; counter++)
                {
                    JSONObject jsonObject = jsonArray.getJSONObject(counter);
                    int userid = jsonObject.getInt("userId");
                    int id = jsonObject.getInt("id");
                    String title = jsonObject.getString("title");
                    boolean completed = jsonObject.getBoolean("completed");

                    ToDo toDo = new ToDo(userid , id , title , completed);

                    alltodo.add(toDo);
                }
            }

        }
        catch (Exception c)
        {
            c.printStackTrace();
        }
        return alltodo;
    }

    @Override
    protected void onPostExecute(ArrayList<ToDo> toDos) {
        progressDialog.dismiss();
        onTaskCompleteTodo.OnCompleteListner();
    }
}

【问题讨论】：

你的 getView 方法返回一些空值。
显示你的数组适配器的getCount()、getItemId()等
不知道为什么这个问题被标记为重复，因为它比重复原因中提到的更特殊。到目前为止，我在自定义 TextView 和自定义属性方面遇到了同样的问题。还是解决不了。

标签： android nullpointerexception custom-lists

【解决方案1】：

您的 ArrayList，“all”，可能尚未初始化。 That's why you get a nullpointerexception。检查你在哪里初始化它并确保代码首先运行并且你应该很好。如果您想确定您的代码在哪里失败，我建议您在带有断点并单步执行的调试器中运行它。

【讨论】：

【解决方案2】：

在 onCreate 中实例化您的数组列表。

all = new Arraylist<>();

这很可能会解决您的问题。如果不发布新的堆栈跟踪

【讨论】：

好吧......无论如何这将防止另一个 NullPointerException
尝试 convertView = LayoutInflater.from(getContext()).inflate(R.layout.listt_item, parent, false); ......删除你的会员inflater并直接使用它。