Question

this question is really wierd and driving me crazy. i can t get rid of the nullPointerException. my task is quite simple, just run a test on the tabhost. but now i m not able to even create one tabhost! in order to ceate a tabhost, there some points i need to be careful with. first there must be a tabwidget with an id of "@android:id/tabs" and a framelayout of which the id is "@android:id/tabconent". i swear i do pay attention and you can see that in my codes below. and i read my articles recommanding using TabActivity. but unfortunately this tabhost will be a component of an activity. so i have to create it in a normal activity.

当代码进入“ addspec () ” 时, 它会抛出一个无效的点数例外。我检查标签 Host 和 Host 。请在 Logcat 中检查。两者都不是无效的! 我将在问题结尾处添加我的打印输出结果。

这是我的java代码。

public class Cao extends Activity {
ScrollView menu_scroll;
TabHost menu_host;
TabWidget menu_tags;
int[] contents;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.testtab);
    menu_host = (TabHost) findViewById(R.id.tabhost);
    Log.e("tabhost", (menu_host == null) + "");
    menu_tags = (TabWidget) findViewById(android.R.id.tabs);
    contents = new int[] { R.id.b1, R.id.b2 };
    int count = 6;
    for (int i = 0; i < count; i++) {
        TabSpec spec = menu_host.newTabSpec(i + "");
        spec.setIndicator("no " + i);
        Log.e("spec", (spec == null) + "");
        spec.setContent(R.id.b1); **// the problem occurs at this line**
        menu_host.addTab(spec);
    }
}
}

我的xml 代码如下

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

<TabHost
    android:id="@+id/tabhost"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="50dp"
        android:orientation="vertical" >

        <HorizontalScrollView
            android:id="@+id/menu_scroll"
            android:layout_width="fill_parent"
            android:layout_height="50dp"
            android:scrollbars="none" >

            <TabWidget
                android:id="@android:id/tabs"
                android:layout_width="fill_parent"
                android:layout_height="wrap_content" >
            </TabWidget>
        </HorizontalScrollView>
    </LinearLayout>

    <FrameLayout
        android:id="@android:id/tabcontent"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" >

        <Button
            android:id="@+id/b1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="1" />

        <Button
            android:id="@+id/b2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="2" />

    </FrameLayout>
</TabHost>

</LinearLayout>

此外,对数打印出

tabhost(490): false
spec(490): false
E/AndroidRuntime(490): Uncaught handler: thread main exiting due to uncaught exception  
E/AndroidRuntime(490): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.tim.wirelessorder/com.tim.wirelessorder.ui.Cao}: java.lang.NullPointerException   
E/AndroidRuntime(490):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2496)
E/AndroidRuntime(490):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512)
E/AndroidRuntime(490):  at android.app.ActivityThread.access$2200(ActivityThread.java:119)
E/AndroidRuntime(490):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863)
E/AndroidRuntime(490):  at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime(490):  at android.os.Looper.loop(Looper.java:123)
E/AndroidRuntime(490):  at android.app.ActivityThread.main(ActivityThread.java:4363)
E/AndroidRuntime(490):  at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(490):  at java.lang.reflect.Method.invoke(Method.java:521)
E/AndroidRuntime(490):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
E/AndroidRuntime(490):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
E/AndroidRuntime(490):  at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime(490): Caused by: java.lang.NullPointerException    
E/AndroidRuntime(490):  at android.widget.TabHost$ViewIdContentStrategy.<init>(TabHost.java:583)
E/AndroidRuntime(490):  at android.widget.TabHost$ViewIdContentStrategy.<init>(TabHost.java:578)
E/AndroidRuntime(490):  at android.widget.TabHost$TabSpec.setContent(TabHost.java:435)
E/AndroidRuntime(490):  at com.tim.wirelessorder.ui.Cao.onCreate(Cao.java:38)
E/AndroidRuntime(490):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
E/AndroidRuntime(490):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459)

Answer 1

将您的标签主机id改成

<TabHost 
    android:id="@android:id/tabhost"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">

/你的活动延伸缩放像这样的活动低于1

public class HelloTabWidget extends TabActivity {

在你的Create上做这个

 TabHost tabHost = getTabHost();  // The activity TabHost
    TabHost.TabSpec spec;  // Resusable TabSpec for each tab
    Intent intent;  // Reusable Intent for each tab

< a href="""http:// developer.android.com/resources/tutors/tutorics/views/ hello-tabwidget.html" rel="nofollow" 请选中:

Answer 2

you need 至extend TabActivity not simple activity try

public class Cao extends TabActivity

整数

public class Cao extends Activity

更改此变化

menu_host = (TabHost) findViewById(R.id.tabhost);

至 menu_host =getTabHost(); and

 android:id="@+id/tabhost"

至

android:id="@android:id/tabhost"

Answer 3

我所需要的只是改变我在.xml中宣布 TabHost 的代号的方式。我使用的不是 "id/tabhost" ,而是 @android:id/tabhost> 。然后,在指定代码中的 TabHost 时,我称之为 findVibById( and mid.R.id.id.tabhost) 。这无论出于何种原因,都解决了我的问题。

友情链接