I am using below code to create three tab in activity but it gives me null pointer exception when I add tab using addtab method.
tabHost.addTab(firstTabSpec);//Null Pointer error occured here
tabHost.addTab(secondTabSpec);
tabHost.addTab(thirdTabSpec);
Below is my Code both layout xml file and onCreaate() method where I create tabs and put actvity in it.
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
try {
/** TabHost will have Tabs */
TabHost tabHost = (TabHost) findViewById(android.R.id.tabhost);
/**
* TabSpec used to create a new tab. By using TabSpec only we can
* able to setContent to the tab. By using TabSpec setIndicator() we
* can set name to tab.
*/
/** tid1 is firstTabSpec Id. Its used to access outside. */
TabSpec firstTabSpec = tabHost.newTabSpec("tid1");
TabSpec secondTabSpec = tabHost.newTabSpec("tid1");
TabSpec thirdTabSpec = tabHost.newTabSpec("tid1");
/** TabSpec setIndicator() is used to set name for the tab. */
/**
* TabSpec setContent() is used to set content for a particular tab.
*/
firstTabSpec.setIndicator("Update-1").setContent(
new Intent(this, Keyboard.class));
secondTabSpec.setIndicator("Update-2").setContent(
new Intent(this, Sensors.class));
thirdTabSpec.setIndicator("Update-3").setContent(
new Intent(this, Relays.class));
/** Add tabSpec to the TabHost to display. */
tabHost.addTab(firstTabSpec);//Null Pointer error occured here
tabHost.addTab(secondTabSpec);
tabHost.addTab(thirdTabSpec);
} catch (Exception e) {
e.printStackTrace();
}
}
Layout main.xml file code
<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="@android:id/tabhost"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<LinearLayout
android:id="@+id/LinearLayout01"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TabWidget
android:id="@android:id/tabs"
android:layout_width="fill_parent"
android:layout_height="wrap_content" >
</TabWidget>
<FrameLayout
android:id="@android:id/tabcontent"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
</FrameLayout>
</LinearLayout>
</TabHost>
Edited XML file
<?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/tabhost1"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<LinearLayout
android:id="@+id/LinearLayout01"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TabWidget
android:id="@android:id/tabs"
android:layout_width="fill_parent"
android:layout_height="wrap_content" >
</TabWidget>
<FrameLayout
android:id="@android:id/tabcontent"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
</FrameLayout>
</LinearLayout>
</TabHost>
</LinearLayout>
Logcat:
java.lang.NullPointerException
at android.widget.TabHost.addTab(TabHost.java:221)
at com.android.embededconversation.EmbededConversation.onCreate(EmbededConversation.java:51)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1615)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
at android.app.ActivityThread.access$1500(ActivityThread.java:117)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:130)
at android.app.ActivityThread.main(ActivityThread.java:3687)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:507)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625)
at dalvik.system.NativeStart.main(Native Method)
This is wrong
TabHost tabHost = (TabHost) findViewById(android.R.id.tabhost);
you are trying to inflate from the wrong resource and the tabHost stays null, always.
change it to :
TabHost tabHost = (TabHost) findViewById(R.id.tabhost);
And make sure you include the correct R (your project's R, not android.R)
EDIT
If you're using TabActivity, the way to fetch the TabHost is, I added an example from an application I wrote:
your TabActivity
:
public class yourTabActivity extends TabActivity
{
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main_tab_widget);
// fetch the TabHost
final TabHost tabHost = (TabHost) getTabHost();
// create Tabs
tabHost.addTab(createTab(yourActivity.class,
"tag", "yourTabTitle", R.drawable.tv));
}
private TabSpec createTab(final Class<?> intentClass, final String tag, final String title, final int drawable)
{
final Intent intent = new Intent().setClass(this, intentClass);
final View tab = LayoutInflater.from(getTabHost().getContext()).inflate(R.layout.tab, null);
((TextView) tab.findViewById(R.id.tab_text)).setText(title);
((ImageView) tab.findViewById(R.id.tab_icon)).setImageResource(drawable);
return getTabHost().newTabSpec(tag).setIndicator(tab).setContent(intent);
}
}
main_tab_widget.xml
<?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="@android:id/tabhost"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<LinearLayout
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<HorizontalScrollView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:scrollbars="none" >
<TabWidget
android:id="@android:id/tabs"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
</HorizontalScrollView>
<FrameLayout
android:id="@android:id/tabcontent"
android:layout_width="fill_parent"
android:layout_height="fill_parent" />
</LinearLayout>
</TabHost>
</LinearLayout>
example for tab.xml. this is actually a custom tab.
<?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:background="@drawable/tab_bg_selector"
android:gravity="center"
android:orientation="vertical"
android:padding="5dp">
<ImageView android:id="@+id/tab_icon"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:scaleType="fitCenter" />
<TextView android:id="@+id/tab_text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:singleLine="true"
android:textStyle="bold"
android:gravity="center_horizontal"
android:textSize="10sp"
android:ellipsize="marquee"
android:textColor="@android:color/black" />
</LinearLayout>
This should cover everything you need for a tab widget...
你需要使用@ + id / someid,或者使用tabActivity并通过getTabHost()获取tabhost
Use android:id="@android:id/tabhost" in the xml property of TabHost :
<TabHost
android:id="@android:id/tabhost"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android">
<!-- other code for tab widget and Frame -->
</TabHost>
and in the source file use :
TabHost tabHost = getTabHost();
to get the tabHost.
<TabHost xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@android:id/tabhost"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
// Your Code Here.
</TabHost>
This is your xml for tabs . For this
TabHost tabHost = getTabHost();
in code to get tabhost reference.
TabSpec firstTabSpec = tabHost.newTabSpec("tid1")
.setIndicator("Update-1")
.setContent(new Intent(this, Keyboard.class));
Apply this for another tabs also.
tabHost.addTab(firstTabSpec);
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