由于 NullPointerException 无法实例化 android.app.Application [英] android.app.Application cannot be instantiated due to NullPointerException
问题描述
我是 android 世界的菜鸟，正在做一个锻炼的宠物项目.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 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.里面有一个按钮可以通向之前的 ListView 活动.
I'm kind of a noob in the android world, and doing a pet project for exercising. It's a very simple reminder-like app with just two activities. One is a customized ListView display the existing alarms. There are some buttons in it to start the other one, which is for add/edit alarms. There is a button in it lead to the previous ListView activity.
我最近遇到了一个奇怪的情况.我的应用程序运行良好.但问题是，每当我触发添加/编辑活动，然后返回到 ListView，并重新运行(或者我应该说重新安装?)应用程序.将弹出错误消息.但它只会短暂显示，应用程序将启动.
There is a weird situation I ran into recently. My app works fine. But the problem is, whenever I trigger the add/edit activity then go back to the ListView, and re-run(or I should say re-install?) the app. An error message will popup. But it will only show up briefly and the the app will start.
我在日志中发现的错误信息说:
The error message I caught in the log says:
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哪里有问题.所以我不知道如何纠正它.有没有人遇到过类似的问题?任何建议将不胜感激！
It doesn't explicitly point out where is wrong in my codes. So I don't have a clue about how to correct it. Does anyone encountered similar problem? Any suggestion will be appreciated!
这是添加/编辑活动的代码:
Here is codes of add/edit activity:
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));
}
}
}
清单是这样的:
<?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>
推荐答案
我做了一些更多的测试并锁定了返回按钮的匿名内部类中的问题，因为每当我在重新启动应用程序之前单击它时都会出现错误.如果我使用手机上的返回"按钮切换活动，则一切正常.
I did some more tests and lockon the problem in the anonymous inner class for Back button, since the error will appear whenever I clicked this before restarting the app. If I switch activities using the "go back" button on the phone, everything is fine.
我在内部类中加了一行
EditEntry.this.finish();
它确实解决了问题.这次我试着更系统地测试它.假设没有上一行的代码是A，有这一行的代码是B.场景如下
It does solve the problem. I tried to test it more systematical this time. Let's say the code without the above line is A, and the code with this line is B. Scenario goes like follow
1.run A then A --> 错误
1.run A then A --> Error
2.run A then B --> 错误
2.run A then B --> Error
3.运行 B 然后运行 A --> OK
3.run B then A --> OK
4.运行 B 然后运行 B --> OK
4.run B then B --> OK
因此，我认为这是关于活动堆栈的某种问题?
Therefore, I assume it is some kind of problem about the activity stack?
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