我正在尝试将自定义 ArrayList 保存到 SharedPreferences。理想情况下,该应用程序第一次运行时,应该有一个空的 SharedPreferences,但如果我需要用一个项目填充它,那么我可以使用“示例”来完成。 我尝试使用调试断点并将问题隔离到下面标记的 setAdapter 行。
应用程序在 setAdapter 行崩溃,但这可能是由于编辑器未初始化?调试器告诉我“editor = null”
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(在注释中提到),我的调试器告诉我“editor = null”。然后执行以下步骤会崩溃并显示以下 logcat。
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!
最佳答案
在实际初始化编辑器
之前,您正在调用save
,它会使用editor
也许将顺序更改为
sharedPref = this.getSharedPreferences("com.lochdownstudios.simplePurchaseOrderer",
Context.MODE_PRIVATE);
editor = sharedPref.edit();
save();
关于java - 使用 SharedPreferences 进行自定义 ArrayList - 适配器或编辑器错误?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/39112942/