启动新活动时出现空指针异常

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

好的,当我开始我的第三个活动时,我得到一个空指针异常。这是LogCat消息:

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:

以下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,"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:

这里是一个名为的新活动类:

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:

这是showdescription.xml文件:

<?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>

3 个解决方案

#1

This is your clue, from the stack trace:

这是你的线索,来自堆栈跟踪:

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?

ShowDescription.java中的第47行是什么?

#2

If I understood the code right, you should invoke the findViewById() of the showdescription view that you set for the activity and not of the activity, because both, button and textview, seem to be part of that view:

如果我理解正确的代码,你应该调用你为活动而不是活动设置的showdescription视图的findViewById(),因为按钮和textview似乎都是该视图的一部分:

super.onCreate(icicle);
View showdescription = this.findViewById(R.id.showdescription);
setContentView(showdescription);

// ..

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

Button backbutton = (Button)showdescription.findViewById(R.id.back);
backbutton.setOnClickListener(new Button.OnClickListener() 
{
    public void onClick(View v) 
    {
        finish();
    }
});

#3

what is the 47 line in your ShowDescription code? I think you are passing a null cursor.

您的ShowDescription代码中的47行是什么?我认为你传递的是一个空游标。

#1