我在android系统中是个菜鸟,并且正在做一个宠物项目来锻炼身体。这是一个非常简单的类似提醒的应用程序,只有两个活动。一种是自定义的ListView,用于显示现有警报。其中有一些按钮可以启动另一个按钮,用于添加/编辑警报。其中有一个按钮可引至上一个ListView活动。
我最近遇到了一个奇怪的情况。我的应用程序运行正常。但是问题是,每当我触发添加/编辑活动,然后返回到ListView,然后重新运行(或者我应该说重新安装?)该应用程序。将会弹出一条错误信息。但是它只会短暂显示,并且该应用程序将启动。
我在日志中捕获的错误消息显示:
FATAL EXCEPTION: main java.lang.RuntimeException: Unable to instantiate application android.app.Application: java.lang.NullPointerException at android.app.LoadedApk.makeApplication(LoadedApk.java:482) at android.app.ActivityThread.handleBindApplication(ActivityThread.java:3909) at android.app.ActivityThread.access$1300(ActivityThread.java:122) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1184) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:137) at android.app.ActivityThread.main(ActivityThread.java:4340) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:511) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.NullPointerException at android.app.LoadedApk.initializeJavaContextClassLoader(LoadedApk.java:362) at android.app.LoadedApk.getClassLoader(LoadedApk.java:305) at android.app.LoadedApk.makeApplication(LoadedApk.java:474) ... 11 more
它没有明确指出我的代码中哪里出了问题。所以我不知道如何纠正它。有没有人遇到类似的问题?任何建议将不胜感激!
这是添加/编辑活动的代码:
public class EditEntry extends Activity { private AutoCompleteTextView foodNameTextView; private DatePicker datePicker; // store values in AutoCompleteTextView & DatePicker private String foodName; private Calendar foodDate; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.edit); // dummy selections for AutoCompleteTextView String[] foodList = new String[]{"meat", "fruit", "vega"}; // instantiate AutoCompleteTextView & DatePicker ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(this, R.layout.food_list_dropdown, foodList); foodNameTextView = (AutoCompleteTextView)findViewById(R.id.foodName); foodNameTextView.setAdapter(arrayAdapter); datePicker = (DatePicker)findViewById(R.id.date_picker); // get intent from ReminderList. Intent intent = getIntent(); // get extras from intent. Return null if intent is sent from "add" action. foodName = intent.getStringExtra("foodName"); foodDate = (Calendar) intent.getSerializableExtra("foodDate"); // set default values for widgets if it is an "edit" action. if (null != foodName) { foodNameTextView.setText(foodName); datePicker.init(foodDate.get(Calendar.YEAR), foodDate.get(Calendar.MONTH), foodDate.get(Calendar.DAY_OF_MONTH), new OnDateChangedListener() { // will implement date input check later. @Override public void onDateChanged(DatePicker view, int year, int monthOfYear, int dayOfMonth) {} }); } // Submit will add/modify the data in xml file. Back will start ReminderList activity Button submit = (Button)findViewById(R.id.entry_submit); Button back = (Button)findViewById(R.id.entry_back); submit.setOnClickListener(new SubmitButtonListener()); back.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { Intent intent = new Intent(); intent.setClass(EditEntry.this, FoodReminderList.class); startActivity(intent); } }); } // add or modify data in xml file @SuppressWarnings("unused") class SubmitButtonListener implements OnClickListener { Calendar foodDate = Calendar.getInstance(); @Override public void onClick(View v) { XmlUtil xmlUtil = new XmlUtil(); // determine if it is an "edit" action. if (null != foodName) { FoodInfo foodInfo = new FoodInfo(foodName, foodDate); // delete the old data entry xmlUtil.deleteEntry(foodInfo); // cancel old alarm FoodReceiver alarm = new FoodReceiver(EditEntry.this, foodDate, false); } // get new input values foodName = foodNameTextView.getText().toString(); foodDate.set(datePicker.getYear(), datePicker.getMonth(), datePicker.getDayOfMonth(), 0, 0, 0); // update xml file FoodInfo foodInfo = new FoodInfo(foodName, foodDate); xmlUtil.updateEntry(foodInfo); // set new alarm FoodReceiver alarm = new FoodReceiver(EditEntry.this, foodDate, true); // popup toast confirming the submit Toast.makeText(EditEntry.this, "Reminder Added", Toast.LENGTH_SHORT).show(); // clear widgets foodNameTextView.setText(""); Calendar currentDate = Calendar.getInstance(); datePicker.updateDate(currentDate.get(Calendar.YEAR), currentDate.get(Calendar.MONTH), currentDate.get(Calendar.DAY_OF_MONTH)); } } }
清单如下所示:
<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="ca.maxiao.Food" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="8" /> <application android:icon="@drawable/ic_launcher" android:label="@string/app_name" > <activity android:label="@string/app_name" android:name=".FoodReminderList" > <intent-filter > <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> <activity android:label="@string/app_name" android:name=".EditEntry" > </activity> <activity android:label='@string/app_name' android:name=".FoodReminder"></activity> <receiver android:name="ca.maxiao.Food.FoodReceiver"> <intent-filter> <action android:name="Alarm_Setting" /> </intent-filter> </receiver> </application> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/> <uses-permission android:name="android.permission.VIBRATE"/> </manifest>
我做了一些测试,并将问题锁定在“后退”按钮的匿名内部类中,因为在重新启动应用程序之前,每当我单击此错误时,都会出现错误。如果我使用手机上的“返回”按钮切换活动,则一切正常。
我在内部类中添加了一行
EditEntry.this.finish();
它确实解决了问题。这次我试图对其进行更系统的测试。假设没有上述行的代码是A,而具有此行的代码是B。场景如下
1.运行A然后A->错误
2.运行A然后B->错误
3.运行B然后A->确定
4.运行B然后B->确定
因此,我假设这是有关活动堆栈的某种问题?