Question

我正在尝试创建一个内部通信应用，但是当我尝试运行它时，它会一直给我一个< Inventory id: nil, amt_sold: 175.0>的错误。
任何人都可以帮我这个吗？

getContext() is null

这是我的logcat

public class intercomApp extends Application {

protected static final String SHARED_PREFS_REFERENCE_LABEL = "ComeNChat";

protected static final String DEFAULT_NAME = "Default_Name";

private static intercomApp instance;

public static intercomApp getInstance() {
    return instance;
}

public static Context getContext() {
    return instance;
}

@Override
public void onCreate() {
    instance = this;
    super.onCreate();
}

// store our name to shared prefs
public static void storeName(String name) {
    PreferenceManager.getDefaultSharedPreferences(getContext()).edit().putString(SHARED_PREFS_REFERENCE_LABEL, name).commit();
}

// get our name from shared prefs
public static String getName() {
    return PreferenceManager.getDefaultSharedPreferences(getContext()).getString(SHARED_PREFS_REFERENCE_LABEL, DEFAULT_NAME); //(intercomApp.java:45)
}

虽然这是MainActivity中使用的功能

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ricky.comenchat/com.example.ricky.comenchat.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
                                                                             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2450)
                                                                             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2520)
                                                                             at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1363)
                                                                             at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                             at android.os.Looper.loop(Looper.java:148)
                                                                             at android.app.ActivityThread.main(ActivityThread.java:5466)
                                                                             at java.lang.reflect.Method.invoke(Native Method)
                                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                          Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
                                                                             at android.preference.PreferenceManager.getDefaultSharedPreferencesName(PreferenceManager.java:375)
                                                                             at android.preference.PreferenceManager.getDefaultSharedPreferences(PreferenceManager.java:370)
                                                                             at com.example.ricky.comenchat.util.intercomApp.getName(intercomApp.java:45)
                                                                             at com.example.ricky.comenchat.MainActivity.getClientNameList(MainActivity.java:383)
                                                                             at com.example.ricky.comenchat.MainActivity.setupClientListAdapter(MainActivity.java:214)
                                                                             at com.example.ricky.comenchat.MainActivity.onCreate(MainActivity.java:149)
                                                                             at android.app.Activity.performCreate(Activity.java:6251)

EDITED：下面是我的manifest.xml

public class MainActivity extends AppCompatActivity {

@Overide
protected void onCreate(Bundle savedInstanceState){
     setupList; //(MainActivity.java:149)
}

private void setupList{
     nameList = getNamelist(); //(MainActivity.java:214)
}

private String[] getNamelist(){
     ArrayList<String> names = new ArrayList<>();
     names.add(intercomApp.getName()); //(MainActivity.java:383)
}

Answer 1

您的Manifest中似乎缺少Application，因此Context为null

<application
    android:name=".util.intercomApp"
    android:allowBackup="true"

旁注：Java约定 - 类名称应以大写字母

开头

Answer 2

而不是像这样创造一个瞬间

public static intercomApp getInstance() {
    return instance;
}

public static Context getContext() {
    return instance;
}

您可以执行以下操作，并使IntercomApp类具有通用性，如下所示

public class IntercomApp {

    protected static final String SHARED_PREFS_REFERENCE_LABEL = "ComeNChat";
    protected static final String DEFAULT_NAME = "Default_Name";

    // store our name to shared prefs
    public static void storeName(String name, Context context) {
        PreferenceManager.getDefaultSharedPreferences(context).edit().putString(SHARED_PREFS_REFERENCE_LABEL, name).commit();
    }

    // get our name from shared prefs
    public static String getName(Context context) {
        return PreferenceManager.getDefaultSharedPreferences(context).getString(SHARED_PREFS_REFERENCE_LABEL, DEFAULT_NAME); //(intercomApp.java:45) 
    }        
}

并在您的任何活动中使用它，如下所示

public class MainActivity extends AppCompatActivity {
    private Context context;

    @Overide
    protected void onCreate(Bundle savedInstanceState){
        context = this;
        setupList(); //(MainActivity.java:149)
    }

    private void setupList() {
        nameList = getNamelist(); //(MainActivity.java:214)
    }

    private String[] getNamelist(){
        ArrayList<String> names = new ArrayList<>();
        names.add(IntercomApp.getName(context)); //(MainActivity.java:383)
    }
}

PreferenceManager.getDefaultSharedPreferences（getContext（））为null

2 个答案: