Error: Can't get to call method from non-activity class - generates NullPointerException error

Question

我有两个 classes：带有 activity xml 文件的 NewAppointment 和扩展 NewAppointment 的 GenerateTreatmentList。在 xml 中，我有一个按钮，它应该显示一个在 GenerateTreatmentLis 中实现的 AlertDialog 列表，如下所示：

import android.app.AlertDialog;
import android.content.Context;

import android.content.DialogInterface;


public class GenerateTreatmentList extends NewAppointment {

public void generateList(){

    final int[] listTitle = new int[1];
    final String[][] listCategories = new String[1][1];
    final int[] categoryArray = new int[1];

    listTitle[0] = R.string.title_category;
    categoryArray[0] = R.array.categories;
    listCategories[0] = getResources().getStringArray(categoryArray[0]);

    chooseTreatmentList(this, listTitle[0], listCategories[0], true, new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            switch (which) {
                // Abonamente category
                case 0:
                {
                    listTitle[0] = R.string.title_abonament;
                    categoryArray[0] = R.array.abonamente;
                    listCategories[0] = getResources().getStringArray(categoryArray[0]);

                    chooseTreatmentList(context, listTitle[0], listCategories[0], true, new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {

                            switch (which) {
                                //Abonament - Vacuum corporal
                                case 0:
                                {
                                    listTitle[0] = R.string.title_timp;
                                    categoryArray[0] = R.array.ab_vacuum_time;
                                    listCategories[0] = getResources().getStringArray(categoryArray[0]);

                                    // Extract the treatment name
                                    treatmentChosen = R.string.vacuum_corp_name;

                                    chooseTreatmentList(context, listTitle[0], listCategories[0], true, new DialogInterface.OnClickListener() {
                                        @Override
                                        public void onClick(DialogInterface dialog, int which) {
                                            // Extract treatment duration
                                            switch (which) {
                                                // Abonament - Vacuum corporal - 60 min
                                                case 0:
                                                {
                                                    treatmentDuration = R.string.name_60_min;


                                                } break;
                                                // Abonament - Vacuum corporal - 30 min
                                                case 1:
                                                {
                                                    treatmentDuration = R.string.name_30_min;
                                                } break;
                                                default: break;
                                            }

                                        }
                                    });
                                } break;
                                // Abonament - Ultrasunete
                                case 1:
                                {

                                } break;
                                //Abonament - Microdermoabraziune
                                case 2:
                                {

                                } break;
                                //Abonament - Electrostimulator
                                case 3:
                                {

                                } break;
                                default: break;
                            }

                        }
                    });
                } break;
                // Tratamente category
                case 1:
                {
                    listTitle[0] = R.string.title_tratament;
                    categoryArray[0] = R.array.tratamente;
                    listCategories[0] = getResources().getStringArray(categoryArray[0]);

                    chooseTreatmentList(context, listTitle[0], listCategories[0], true, new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {

                        }
                    });
                } break;
                // Epilare category
                case 2:
                {
                    listTitle[0] = R.string.title_epilare;
                    categoryArray[0] = R.array.epilari;
                    listCategories[0] = getResources().getStringArray(categoryArray[0]);

                    chooseTreatmentList(context, listTitle[0], listCategories[0], true, new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {

                        }
                    });
                } break;
                // Masaje category
                case 3:
                {
                    listTitle[0] = R.string.title_masaj;
                    categoryArray[0] = R.array.masaje;
                    listCategories[0] = getResources().getStringArray(categoryArray[0]);

                    chooseTreatmentList(context, listTitle[0], listCategories[0], true, new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {

                        }
                    });
                } break;
                default:
                    break;
            }

        }
    });

}

private static void chooseTreatmentList(Context context, int listTitle,
                                        String[] listElements,
                                        boolean OnClickListener,
                                        DialogInterface.OnClickListener selectedItemListener) {

    AlertDialog.Builder treatmentList = new AlertDialog.Builder(context);
    treatmentList.setTitle(listTitle);
    treatmentList.setItems(listElements, selectedItemListener);
    treatmentList.create().show();
}
}

Dialog list每次都要打开另一个dialog list，以此类推，直到某个点（还没有完成所有选项）。如果我将所有代码从 GenerateTreatmentList 移动到 NewAppointment class，它工作正常，但这是我试图避免的事情，因为我会溢出 class.

当我按下按钮时，应用程序在 phone 上重新启动，我收到以下错误：

java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.res.Resources android.content.Context.getResources()' on a null object reference
        at android.content.ContextWrapper.getResources(ContextWrapper.java:89)
        at android.view.ContextThemeWrapper.getResourcesInternal(ContextThemeWrapper.java:127)
        at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:121)
        at android.support.v7.app.AppCompatActivity.getResources(AppCompatActivity.java:542)
        at com.andygix.programarilucia.GenerateTreatmentList.generateList(GenerateTreatmentList.java:18)

第 18 行：

listCategories[0] = getResources().getStringArray(categoryArray[0]);

起初我以为是缺少上下文传递，但是我尝试了几种方法都没有用。不幸的是，现在我被卡住了，但不想将这部分移动到 NewAppointment class。

有什么想法吗？

编辑：忘记提及从 NewAppointment 调用方法 class

GenerateTreatmentList getList = new GenerateTreatmentList();
getList.generateList();

Answer 1

我似乎找到了解决问题的方法。我做了以下更改：

在 GenerateTreatmentList class 中，我创建了一个使用 class 名称和上下文作为参数的方法。

private Context context;

    public GenerateTreatmentList (Context context) {
        this.context = context;
    }

然后，在尝试访问资源时，我还在给定字符串或数组列表的路径之前添加了上下文

listCategories[0] = context.getResources().getStringArray(categoryArray[0]);

在 NewAppointment class 中，当尝试调用非 activity 时，我传递了上下文：

   public void chooseTreatment() {
        GenerateTreatmentList getList = new GenerateTreatmentList(this);
        getList.generateList();
   }

我知道我的代码看起来很草率，那是因为我是新手。我一般都是扩展写的，看看能不能行，再简化一下。

Error: Can't get to call method from non-activity class - generates NullPointerException error

Error: Can't get to call method from non-activity class - generates NullPointerException error

java

android

nullpointerexception

android-context