在初始化适配器时出现了Java.lang.NullPointerException错误，错误位于getapplicationContext()函数。

Question

在Android模拟器上运行项目时，我遇到了一个异常问题，错误提示为java.lang.NullPointerException at getApplicationContext。请帮助我解决这个问题。

错误信息：

07-19 15:08:07.811: D/AndroidRuntime(366): Shutting down VM
07-19 15:08:07.811: W/dalvikvm(366): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
07-19 15:08:07.841: E/AndroidRuntime(366): FATAL EXCEPTION: main
07-19 15:08:07.841: E/AndroidRuntime(366): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{org.TfsMutualFund/org.TfsMutualFund.loading}: java.lang.NullPointerException
07-19 15:08:07.841: E/AndroidRuntime(366):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585)
07-19 15:08:07.841: E/AndroidRuntime(366):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)

07-19 15:08:07.841: E/AndroidRuntime(366): Caused by: java.lang.NullPointerException
07-19 15:08:07.841: E/AndroidRuntime(366):  at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:100)
07-19 15:08:07.841: E/AndroidRuntime(366):  at org.TfsMutualFund.loading.<init>(loading.java:23)

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
 package="org.TfsMutualFund">   
<uses-sdk android:targetSdkVersion="8" />

<application android:name=".globalAdapter" android:icon="@drawable/icon" android:label="@string/app_name">

    <activity android:name=".loading"
              android:label="@string/app_name"
              android:theme="@android:style/Theme.NoTitleBar"
              android:configChanges="orientation|keyboard|keyboardHidden">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity android:name=".TFSManinActivity"
    android:configChanges="orientation|keyboard|keyboardHidden"/>
</application>

loading.java

package org.TfsMutualFund;

public class loading extends Activity{
private static ArrayAdapter<String> adapter;
private globalAdapter adpt = ((globalAdapter)getApplicationContext());
private String ServicePath = adpt.getServicePath();
private String ServiceName = adpt.getServiceName();
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.loading);
 if(isOnline())
    new AsyncLoad().execute();
 else

- Mahavir

---

在您的加载活动中，您可以只使用“this”而不是调用getApplicationContext()。 - pixelscreen

只发布出现错误的代码块！！！ - Ram kiran Pachigolla

还有，那些初始化操作应该在onCreate()中进行，而不是在它之前！ - pixelscreen

Answer 1

不要在OnCreate()之前初始化，因为你无法在那里获取Context，应该在onCreate()中进行。

private globalAdapter adpt;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.loading);
    adpt  = ((globalAdapter)getApplicationContext());
    ...
}

- Lalit Poptani

---

谢谢Lalit。但是在OnCreate方法中初始化后，它仍然显示相同的错误。 - Mahavir

你把 private globalAdapter adpt = ((globalAdapter)getApplicationContext()); 作为全局变量移除了吗？ - Lalit Poptani

我将其声明为全局变量，并在Oncreate()方法中进行初始化。 - Mahavir

Answer 2

1. 不要在onCreate之前初始化下面的内容，让视图先获取它们的ID。

private globalAdapter adpt = ((globalAdapter)getApplicationContext());
private String ServicePath = adpt.getServicePath();
private String ServiceName = adpt.getServiceName();

2. 只需声明它们...

private globalAdapter adpt;
private String ServicePath;  
private String ServiceName;

3. 这是因为当Activity还没有被创建时，你怎么能获得到它的上下文呢？因为你正在使用getApplicationContext()方法来获取当前Activity的上下文。

- Dhruvil Patel

---

谢谢Xitij，但即使在Oncreate()方法中初始化它，它仍然显示相同的错误。 - Mahavir