使用SharedPreferences自定义ArrayList - 适配器或编辑器错误？

Question

我正在尝试将自定义ArrayList保存到SharedPreferences。理想情况下，第一次运行这个应用程序时，应该有一个空的SharedPreferences，但是如果我需要用一个项目填充它，那么我可以用一个“Example”来完成。 我试过使用调试断点并将问题隔离到下面标记的setAdapter行。

该应用程序在setAdapter行崩溃，但它可能是由于编辑器未被初始化？调试器告诉我“编辑=空”

public class MainActivity extends AppCompatActivity { 
    ArrayList<PurchaseOrders> purchaseOrders = new ArrayList<PurchaseOrders>(); 
    PurchaseOrderAdapter adapter; 

    public SharedPreferences sharedPref; 
    public SharedPreferences.Editor editor; 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     purchaseOrders = new ArrayList<PurchaseOrders>(); 

     String[] items = new String[]{"1", "2", "3"}; 

     purchaseOrders.add(new PurchaseOrders(false, "purchaseNumber", "Customer", "Date 1", "Date 2", items)); 

     save(); 

     sharedPref = this.getSharedPreferences("com.lochdownstudios.simplePurchaseOrderer", Context.MODE_PRIVATE); 
     editor = sharedPref.edit(); 

     load(); 

     adapter = new PurchaseOrderAdapter(this, purchaseOrders); 
     final ListView listView = (ListView) findViewById(R.id.listView); 
     listView.setAdapter(adapter); // Break Point here. 
    } 

    private void save() { 
     Gson gson = new Gson(); 
     String json = gson.toJson(purchaseOrders); 
     editor.putString("savedPurchaseOrders", json); //editor = null .... hmmm.... 
     editor.apply(); 
    } 

    private void load() { 
     Gson gson = new Gson(); 
     String json = sharedPref.getString("savedPurchaseOrders", ""); 
     Type type = new TypeToken<List<PurchaseOrders>>(){}.getType(); 
     purchaseOrders = gson.fromJson(json, type); 
    } 
} 

在断点（在评论中提到），我的调试器告诉我，“编辑=空”。然后下面的步骤使用下面的logcat崩溃。

08-23 19:06:02.799 23974-23974/com.lochdownstudios.simplePurchaseOrderer E/AndroidRuntime: FATAL EXCEPTION: main 
Process: com.lochdownstudios.simplePurchaseOrderer, PID: 23974 
java.lang.RuntimeException: Unable to start activity 
ComponentInfo{com.lochdownstudios.simplePurchaseOrderer/com.lochdownstudios.simplePurchaseOrderer.MainActivity}: java.lang.NullPointerException: Attempt to invoke interface method 'android.content.SharedPreferences$Editor android.content.SharedPreferences$Editor.putString(java.lang.String, java.lang.String)' on a null object reference 
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3253) 
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349) 
at android.app.ActivityThread.access$1100(ActivityThread.java:221) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:158) 
at android.app.ActivityThread.main(ActivityThread.java:7224) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120) 
Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'android.content.SharedPreferences$Editor android.content.SharedPreferences$Editor.putString(java.lang.String, java.lang.String)' on a null object reference 
at com.lochdownstudios.simplePurchaseOrderer.MainActivity.save(MainActivity.java:119) 
at com.lochdownstudios.simplePurchaseOrderer.MainActivity.onCreate(MainActivity.java:39) 
at android.app.Activity.performCreate(Activity.java:6876) 
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1135) 
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3206) 
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3349) 
at android.app.ActivityThread.access$1100(ActivityThread.java:221)  
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)  
at android.os.Handler.dispatchMessage(Handler.java:102)  
at android.os.Looper.loop(Looper.java:158)  
at android.app.ActivityThread.main(ActivityThread.java:7224)  
at java.lang.reflect.Method.invoke(Native Method)  
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)  

想法？谢谢！

Answer 1

要调用save它采用editor之前，你实际上是在初始化editor

也许改变以

sharedPref = this.getSharedPreferences("com.lochdownstudios.simplePurchaseOrderer", 
                    Context.MODE_PRIVATE); 
    editor = sharedPref.edit(); 

    save();