Android TabHost.addTab -> Null pointer exception

问题

Here is my code:

    public class Main extends Activity {
        @Override
        public void onCreate(Bundle savedInstanceState) {
            TabHost tabHost = new TabHost(this);

            TabHost.TabSpec tab = tabHost.newTabSpec("tab1");
            tab.setIndicator("Tab 1");
            tab.setContent(new TabHost.TabContentFactory() {
                @Override
                public View createTabContent(String tag) {
                    TextView tv = new TextView(Main.this);
                    tv.setText("tab 1 content");
                    return tv;
                }
            });

            tabHost.addTab(tab);

            setContentView(tabHost);
        }
    }

I get this error:

    [...]
    07-13 20:26:49.261: ERROR/AndroidRuntime(625): Caused by: java.lang.NullPointerException
    07-13 20:26:49.261: ERROR/AndroidRuntime(625):     at android.widget.TabHost.addTab(TabHost.java:206)
    07-13 20:26:49.261: ERROR/AndroidRuntime(625):     at test.test.Main.onCreate(Main.java:27)
    [...]

I need to do this by code and I can't use XML. Can anyone help me fix this code please ?

回答1:

You should use TabActivity, it needs same special layout to be set as content (see http://developer.android.com/resources/tutorials/views/hello-tabwidget.html). If you can not use xml you should construct the same content from java code:

public class Main extends TabActivity {
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    TabHost tabHost = new TabHost(this);
    tabHost.setId(android.R.id.tabhost);

    TabWidget widget = new TabWidget(this);
    widget.setId(android.R.id.tabs);

    FrameLayout content = new FrameLayout(this);
    content.setId(android.R.id.tabcontent);

    LinearLayout layout = new LinearLayout(this);
    layout.setOrientation(LinearLayout.VERTICAL);
    layout.addView(widget);
    layout.addView(content);

    tabHost.addView(layout);

    setContentView(tabHost);

    TabHost.TabSpec tab1 = tabHost.newTabSpec("tab1");
    tab1.setIndicator("Tab 1");
    tab1.setContent(new TabHost.TabContentFactory() {
        @Override
        public View createTabContent(String tag) {
            TextView tv = new TextView(Main.this);
            tv.setText("tab 1 content");
            return tv;
        }
    });

    tabHost.addTab(tab1);

    TabHost.TabSpec tab2 = tabHost.newTabSpec("tab2");
    tab2.setIndicator("Tab 2");
    tab2.setContent(new TabHost.TabContentFactory() {
        @Override
        public View createTabContent(String tag) {
            TextView tv = new TextView(Main.this);
            tv.setText("tab 2 content");
            return tv;
        }
    });

    tabHost.addTab(tab2);

    setContentView(tabHost);
}

}

回答2:

For people who might wonder about TabActivity being deprecated the documentation says that you need to call setup() before adding tabs, when you don't use a TabActivity.

tabHost.setup();

回答3:

Checking the method TabHost.addTab(...) in the framework source suggests that your TabWidget is not available yet. A TabWidget must be created in code first or by the system when creating a layout and must have an id of android.R.id.tabs.

回答4:

Have you thought about extending TabActivity, and then calling getTabHost() to get the instance of the TabHost? Not sure what your objective is, but this might be worth looking at.

来源：https://stackoverflow.com/questions/6685257/android-tabhost-addtab-null-pointer-exception

标签

android

nullpointerexception

android-tabhost