启动新活动时出现空指针异常 [英] null pointer exception when starting new activity

问题描述

好的，当我开始我的第三个活动时，我收到了一个空指针异常.这是 LogCat 消息:

<前>12-28 04:38:00.350:错误/AndroidRuntime(776):java.lang.RuntimeException:无法启动活动组件信息{com.acithium.main/com.acithium.rss.ShowDescription}:java.lang.NullPointerException12-28 04:38:00.350: 错误/AndroidRuntime(776): 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2401)12-28 04:38:00.350: 错误/AndroidRuntime(776): 在 android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2417)12-28 04:38:00.350: 错误/AndroidRuntime(776): 在 android.app.ActivityThread.access$2100(ActivityThread.java:116)12-28 04:38:00.350: 错误/AndroidRuntime(776): 在 android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)12-28 04:38:00.350: 错误/AndroidRuntime(776): 在 android.os.Handler.dispatchMessage(Handler.java:99)12-28 04:38:00.350: 错误/AndroidRuntime(776): 在 android.os.Looper.loop(Looper.java:123)12-28 04:38:00.350: 错误/AndroidRuntime(776): 在 android.app.ActivityThread.main(ActivityThread.java:4203)12-28 04:38:00.350:错误/AndroidRuntime(776):在java.lang.reflect.Method.invokeNative(本地方法)12-28 04:38:00.350: 错误/AndroidRuntime(776): 在 java.lang.reflect.Method.invoke(Method.java:521)12-28 04:38:00.350: 错误/AndroidRuntime(776): 在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)12-28 04:38:00.350: 错误/AndroidRuntime(776): 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:549)12-28 04:38:00.350:错误/AndroidRuntime(776):在dalvik.system.NativeStart.main(本地方法)12-28 04:38:00.350:错误/AndroidRuntime(776):由:java.lang.NullPointerException引起12-28 04:38:00.350: 错误/AndroidRuntime(776): 在 com.acithium.rss.ShowDescription.onCreate(ShowDescription.java:48)12-28 04:38:00.350: 错误/AndroidRuntime(776): 在 android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123)12-28 04:38:00.350: 错误/AndroidRuntime(776): 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364)12-28 04:38:00.350: 错误/AndroidRuntime(776): ... 11 更多

这是我调用活动的代码部分:

public void onItemClick(AdapterView parent, View v, int position, long id){Log.i(tag,"物品被点击！[" + feed.getItem(position).getTitle() + "]");Intent itemintent = new Intent(this,com.acithium.rss.ShowDescription.class);//意图 itemintent = new Intent();//itemintent.setClassName("com.acithium.main", "com.acithium.rss.ShowDescription");Bundle b = new Bundle();b.putString("title", feed.getItem(position).getTitle());b.putString("description", feed.getItem(position).getDescription());b.putString("link", feed.getItem(position).getLink());itemintent.putExtra("android.intent.extra.INTENT", b);startActivityForResult(itemintent,0);}

这里是新的活动类，称为:

公共类 ShowDescription 扩展 Activity{公共无效onCreate(捆绑冰柱){super.onCreate(冰柱)；setContentView(R.layout.showdescription);字符串 theStory = null;意图startingIntent = getIntent();if (startingIntent != null){Bundle b = startingIntent.getBundleExtra("android.intent.extra.INTENT");如果 (b == 空){theStory = "坏包?";}别的{theStory = b.getString("title") + "\n\n" + b.getString("description") + "\n\n更多信息:\n" + b.getString("link");}}别的{theStory = "未找到信息.";}TextView db= (TextView) findViewById(R.id.storybox);db.setText(theStory);按钮 backbutton = (Button) findViewById(R.id.back);backbutton.setOnClickListener(new Button.OnClickListener(){public void onClick(View v){结束();}});}}

这是 showdescription.xml 文件:

<文本视图android:layout_width="fill_parent"android:layout_height="wrap_content"机器人:自动链接=所有"android:text="故事在这里......"android:id="@+id/storybox"/><按钮android:layout_height="wrap_content"机器人:文本=返回"android:id="@+id/back"android:layout_width="100px"android:layout_marginLeft="100px"/></LinearLayout></ScrollView></LinearLayout>

解决方案

这是你的线索，来自堆栈跟踪:

12-28 03:47:21.670: ERROR/AndroidRuntime(862): 引起:java.lang.NullPointerException12-28 03:47:21.670: 错误/AndroidRuntime(862): 在 com.acithium.rss.ShowDescription.onCreate(ShowDescription.java:47)

ShowDescription.java 中的第 47 行是什么?

Okay, I'm getting a null pointer exception when I start my third activity. Here is the LogCat message:

12-28 04:38:00.350: ERROR/AndroidRuntime(776): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.acithium.main/com.acithium.rss.ShowDescription}: java.lang.NullPointerException
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2401)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2417)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.app.ActivityThread.access$2100(ActivityThread.java:116)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1794)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.os.Handler.dispatchMessage(Handler.java:99)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.os.Looper.loop(Looper.java:123)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.app.ActivityThread.main(ActivityThread.java:4203)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at java.lang.reflect.Method.invokeNative(Native Method)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at java.lang.reflect.Method.invoke(Method.java:521)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:549)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at dalvik.system.NativeStart.main(Native Method)
12-28 04:38:00.350: ERROR/AndroidRuntime(776): Caused by: java.lang.NullPointerException
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at com.acithium.rss.ShowDescription.onCreate(ShowDescription.java:48)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1123)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2364)
12-28 04:38:00.350: ERROR/AndroidRuntime(776):     ... 11 more

Here is the section of code where I call the activity:

public void onItemClick(AdapterView parent, View v, int position, long id)
 {
     Log.i(tag,"item clicked! [" + feed.getItem(position).getTitle() + "]");

     Intent itemintent = new Intent(this,com.acithium.rss.ShowDescription.class);
     //Intent itemintent = new Intent();
     //itemintent.setClassName("com.acithium.main", "com.acithium.rss.ShowDescription");
     Bundle b = new Bundle();
     b.putString("title", feed.getItem(position).getTitle());
     b.putString("description", feed.getItem(position).getDescription());
     b.putString("link", feed.getItem(position).getLink());
     itemintent.putExtra("android.intent.extra.INTENT", b);

     startActivityForResult(itemintent,0);
 }

And here is new activity class that is called:

public class ShowDescription extends Activity 
{

    public void onCreate(Bundle icicle) 
    {
        super.onCreate(icicle);
        setContentView(R.layout.showdescription);

        String theStory = null;


        Intent startingIntent = getIntent();


        if (startingIntent != null)
        {
            Bundle b = startingIntent.getBundleExtra("android.intent.extra.INTENT");
            if (b == null)
            {
                theStory = "bad bundle?";
            }
            else
            {
                theStory =  b.getString("title") + "\n\n" + b.getString("description") + "\n\nMore information:\n" + b.getString("link");
            }
        }
        else
        {
            theStory = "Information Not Found.";

        }
        TextView db= (TextView) findViewById(R.id.storybox);
        db.setText(theStory);

        Button backbutton = (Button) findViewById(R.id.back);

        backbutton.setOnClickListener(new Button.OnClickListener() 
        {
            public void onClick(View v) 
            {
                finish();
            }
        });        
    }
}

here is the showdescription.xml file:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <ScrollView android:layout_width="fill_parent"
            android:layout_height="fill_parent" >
            <LinearLayout 
                android:orientation="vertical"
                android:layout_width="fill_parent" 
                android:layout_height="fill_parent">
        <TextView  
             android:layout_width="fill_parent" 
                 android:layout_height="wrap_content" 
                 android:autoLink="all"
                 android:text="story goes here ...."
             android:id="@+id/storybox" />
        <Button
                android:layout_height="wrap_content" 
                android:text="Back"
            android:id="@+id/back" 
            android:layout_width="100px" 
            android:layout_marginLeft="100px"/>   
        </LinearLayout>
    </ScrollView>
</LinearLayout>

解决方案

This is your clue, from the stack trace:

12-28 03:47:21.670: ERROR/AndroidRuntime(862): Caused by: java.lang.NullPointerException
12-28 03:47:21.670: ERROR/AndroidRuntime(862): at com.acithium.rss.ShowDescription.onCreate(ShowDescription.java:47)

What's line 47 in ShowDescription.java?

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