Android：调用新意图时出现空指针异常 [英] Android: Null Pointer Exception when calling new intent
问题描述
尝试通过意图调用新活动时收到错误：
I am receiving an error when trying to call new activity through an intent:
java.lang.NullPointerException: Attempt to invoke virtual method 'android.app.ActivityThread$ApplicationThread android.app.ActivityThread.getApplicationThread()' on a null object reference
我的活动有一个按钮，当点击时，它会转到这个方法：
My Activity has a button, and when clicked, it goes to this method:
public void onClickChangeActivity() {
Intent intent = new Intent(context , Details.class);
startActivity(intent);
}
公共静态上下文上下文是在类的开头创建的然后在我的onCreate中实例化为context = getApplicationContext（）;
public static Context context is created in the beginning of the class and then is instantiated in my onCreate as context = getApplicationContext();
我还尝试了context = getBaseContext（）和context = RecyclerViewActivity.this（RecyclerViewActivity是这个名字）我现在的课程）
I've also tried context = getBaseContext() and context = RecyclerViewActivity.this (RecyclerViewActivity is the name of my current class)
为什么我收到这个NullP的任何帮助？我已经尝试了所有与StackOverFlow相关的答案。另外，我的清单包括我的活动。
Any help as to why I'm receiving this NullP? I've tried everything related StackOverFlow answers have offered. Also, my Manifest includes my activity.
从我的RecyclerViewerAdapter类调用onClickChangeActivity：
onClickChangeActivity is being called from my RecyclerViewerAdapter class:
View.OnClickListener getPersonClickListener(final int position) {
return new View.OnClickListener() {
@Override
public void onClick(View view) {
RecyclerViewActivity recyclerViewActivity = new RecyclerViewActivity();
recyclerViewActivity.onClickChangeActivity();
}
};
清单文件：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.test.akash.android_test" >
<uses-sdk
android:minSdkVersion="16"
android:targetSdkVersion="21" />
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission
android:name="android.permission.WRITE_EXTERNAL_STORAGE"
android:maxSdkVersion="18" />
<uses-permission android:name="android.permission.READ_PHONE_STATE" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission
android:name="android.permission.READ_EXTERNAL_STORAGE"
android:maxSdkVersion="18" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name"
android:screenOrientation="portrait" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<!-- <activity -->
<!-- android:name=".DataFetcher" -->
<!-- android:label="@string/title_activity_data_fetcher" > -->
<!-- </activity> -->
<activity
android:name=".Crime"
android:label="@string/title_activity_crime"
android:screenOrientation="portrait" >
</activity>
<activity
android:name=".RecyclerViewActivity"
android:label="@string/title_activity_recycler_view"
android:screenOrientation="portrait" >
</activity>
<activity
android:name=".Details"
android:label="@string/title_activity_crime_details"
android:parentActivityName=".RecyclerViewActivity" >
<meta-data
android:name="android.support.PARENT_ACTIVITY"
android:value="RecyclerViewActivity" />
</activity>
</application>
</manifest>
LogCat：
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference
at android.content.ContextWrapper.getPackageName(ContextWrapper.java:132)
at android.content.ComponentName.<init>(ComponentName.java:77)
at android.content.Intent.<init>(Intent.java:4160)
at com.bah.baltimoreopendata.android_baltimoreopendata.RecyclerViewActivity.onClickChangeActivity(RecyclerViewActivity.java:265)
at com.bah.baltimoreopendata.android_baltimoreopendata.RecycleViewAdapter$1.onClick(RecycleViewAdapter.java:121)
at android.view.View.performClick(View.java:4780)
at android.view.View$PerformClick.run(View.java:19866)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
推荐答案
问题是你试图从适配器调用活动方法：
Problem is that you are trying to call an activity method from the adapter:
RecyclerViewActivity recyclerViewActivity = new RecyclerViewActivity();
recyclerViewActivity.onClickChangeActivity();
您应该在适配器类中替换此代码。在适配器构造函数中添加以下行：
You should replace this code in adapter class. In the adapter constructor add the following lines:
public RecycleViewAdapter(......, Context context){
...your code.
this.mContext=context;
}
并且在 getPersonClickListener 适配器方法中：
View.OnClickListener getPersonClickListener(final int position) {
return new View.OnClickListener() {
@Override
public void onClick(View view) {
if(mContext instanceof RecyclerViewActivity){
((RecyclerViewActivity)mContext).onClickChangeActivity();
}
}
};
当您在RecyclerViewActivity上调用 onClickChangeActivity 方法时，请使用：
And when you invoke onClickChangeActivity method on RecyclerViewActivity use:
public void onClickChangeActivity() {
Intent intent = new Intent(RecyclerViewActivity.this, Details.class);
startActivity(intent);
}
并确保 Details.class 扩展活动。
这篇关于Android：调用新意图时出现空指针异常的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
