Java 如何修复NullPointerException?(Android SDK,Eclipse)
我觉得这是一个简单的问题,我不知怎么地遗漏了,但我一辈子都无法找出这段代码出了什么问题。每次加载这个类时,我都会得到一个NullPointerExceptionJava 如何修复NullPointerException?(Android SDK,Eclipse),java,android,xml,eclipse,Java,Android,Xml,Eclipse,我觉得这是一个简单的问题,我不知怎么地遗漏了,但我一辈子都无法找出这段代码出了什么问题。每次加载这个类时,我都会得到一个NullPointerException 11-19 17:40:35.967: E/AndroidRuntime(2144): FATAL EXCEPTION: main 11-19 17:40:35.967: E/AndroidRuntime(2144): Process: john.brian.adlibs, PID: 2144 11-19 17:40:35.967: E
11-19 17:40:35.967: E/AndroidRuntime(2144): FATAL EXCEPTION: main
11-19 17:40:35.967: E/AndroidRuntime(2144): Process: john.brian.adlibs, PID: 2144
11-19 17:40:35.967: E/AndroidRuntime(2144): java.lang.RuntimeException: Unable to start activity ComponentInfo{john.brian.adlibs/john.brian.adlibs.StoryDisplay}: java.lang.NullPointerException
11-19 17:40:35.967: E/AndroidRuntime(2144): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2176)
11-19 17:40:35.967: E/AndroidRuntime(2144): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2226)
11-19 17:40:35.967: E/AndroidRuntime(2144): at android.app.ActivityThread.access$700(ActivityThread.java:135)
11-19 17:40:35.967: E/AndroidRuntime(2144): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1397)
11-19 17:40:35.967: E/AndroidRuntime(2144): at android.os.Handler.dispatchMessage(Handler.java:102)
11-19 17:40:35.967: E/AndroidRuntime(2144): at android.os.Looper.loop(Looper.java:137)
11-19 17:40:35.967: E/AndroidRuntime(2144): at android.app.ActivityThread.main(ActivityThread.java:4998)
11-19 17:40:35.967: E/AndroidRuntime(2144): at java.lang.reflect.Method.invokeNative(Native Method)
11-19 17:40:35.967: E/AndroidRuntime(2144): at java.lang.reflect.Method.invoke(Method.java:515)
11-19 17:40:35.967: E/AndroidRuntime(2144): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
11-19 17:40:35.967: E/AndroidRuntime(2144): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
11-19 17:40:35.967: E/AndroidRuntime(2144): at dalvik.system.NativeStart.main(Native Method)
11-19 17:40:35.967: E/AndroidRuntime(2144): Caused by: java.lang.NullPointerException
11-19 17:40:35.967: E/AndroidRuntime(2144): at john.brian.adlibs.StoryDisplay.onCreate(StoryDisplay.java:25)
11-19 17:40:35.967: E/AndroidRuntime(2144): at android.app.Activity.performCreate(Activity.java:5243)
11-19 17:40:35.967: E/AndroidRuntime(2144): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
11-19 17:40:35.967: E/AndroidRuntime(2144): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2140)
11-19 17:40:35.967: E/AndroidRuntime(2144): ... 11 more
而且,在大量的谷歌搜索之后,我很确定一切都被定义了
public class StoryDisplay extends Activity{
TextView storyView;
Button sdBackToStoryList;
ScrollView scrollView;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.story_display);
setVariables();
String story = getIntent().getExtras().getString("storyFinal");
storyView.setText(story);
sdBackToStoryList.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Intent viewChooseStory = new Intent(StoryDisplay.this, ChooseStory.class);
startActivity(viewChooseStory);
}
});
}
private void setVariables() {
// TODO Auto-generated method stub
sdBackToStoryList = (Button) findViewById(R.id.bStoryDisplayBackToStoryList);
storyView = (TextView) findViewById(R.id.tvStoryDisplayStory);
scrollView = (ScrollView) findViewById(R.id.svStoryDisplay);
}
}
以及XML代码:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
xmlns:ads="http://schemas.android.com/apk/lib/com.google.ads"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="0dp" >
<com.google.ads.AdView android:id="@+id/adView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
ads:adUnitId="ca-app-pub-3337976893531833/3006951709"
ads:adSize="BANNER"
ads:testDevices="TEST_EMULATOR, emulator-5554"
ads:loadAdOnCreate="true"
/>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:orientation="vertical"
android:layout_weight="10"
android:padding="20dp" >
<ScrollView
android:layout_width="fill_parent"
android:id="@+id/svStoryDisplay"
android:layout_height="350dp">
<TextView
android:text="@string/app_name"
android:id="@+id/tvStoryDisplayStory"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:gravity="left" />
</ScrollView>
<Button
android:id="@+id/bStoryDisplayBackToStoryList"
android:layout_width="wrap_content"
android:layout_gravity="center"
android:layout_height="50dp"
android:textSize="20sp"
android:text="@string/backToStoryList"
/>
错误出现在以下行中:
storyView.setText(story);
再一次,我确信这是一个非常简单的问题,我只是错过了,我觉得有这个问题非常愚蠢,但任何帮助都将不胜感激。谢谢大家! 在下面的代码中
Intent teleport = new Intent(SadLibs.this, StoryDisplay.class);
teleport.putExtra("storyFinal",storyFinal);
startActivity(teleport);
Intent viewChooseStory = new Intent(SadLibs.this, StoryDisplay.class);
startActivity(viewChooseStory);
您只添加了一次额外的。如果您不添加storyFinal
extra,您将获得NPE
String story = getIntent().getExtras().getString("storyFinal");
您需要检查Intent或Extras是否为NULL
if (getIntent() != NULL) {
if (getIntent().getExtras() != NULL) {
story = getIntent().getExtras().getString("storyFinal");
}
}
检查如下:
if(storyView!=null)
{
storyView.setText(story);
}
实施
sdBackToStoryList = (Button) findViewById(R.id.bStoryDisplayBackToStoryList);
storyView = (TextView) findViewById(R.id.tvStoryDisplayStory);
scrollView = (ScrollView) findViewById(R.id.svStoryDisplay);
在onCreate()中
希望这能有所帮助。请使用实际错误消息(包括堆栈跟踪)进行更新,并指出获取NPEString storyFinal=新字符串的行(“字符串在此显示”);请编辑您的问题并包括堆栈跟踪。注释中显示的行无法生成NPE。
原因:java.lang.NullPointerException 11-19 17:40:35.967:E/AndroidRuntime(2144):在john.brian.adlibs.StoryDisplay.onCreate(StoryDisplay.java:25)
第25行是什么?为什么要创建两个意图
?这是避免NPE的正确方法(虽然我将两个if语句放在同一个语句中),但不清楚的是问题不是他自己的“逻辑”,但我们无法判断在他的应用程序中是否可以使用空的额外值:)当他创建intent viewChooseStory时,没有额外的内容添加到intent中。。。。假设这两段代码来自他的应用程序的不同部分。是的,如果没有访问所有代码的权限,很难判断。
if(storyView!=null)
{
storyView.setText(story);
}
sdBackToStoryList = (Button) findViewById(R.id.bStoryDisplayBackToStoryList);
storyView = (TextView) findViewById(R.id.tvStoryDisplayStory);
scrollView = (ScrollView) findViewById(R.id.svStoryDisplay);