当 tabhost 不是布局中唯一的东西时，Tabhost nullpointerexception

Question

我注意到使用 tabhost 有很多问题，但没有一个真正适合我的问题。我正在尝试创建一个顶部带有action bar 的视图，然后是栏下方的一排选项卡。这是我的活动布局。

<?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"
    style="@style/Dashboard">

    <com.ftni.common.ui.ActionBar
        android:id="@+id/actionbar"
        style="@style/ActionBar"/>

    <TabHost android:id="@android:id/tabhost"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent">
        <LinearLayout
            android:orientation="vertical"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:padding="5dp">
            <TabWidget
                android:id="@android:id/tabs"
                android:layout_width="fill_parent"
                android:layout_height="wrap_content" />
            <FrameLayout
                android:id="@android:id/tabcontent"
                android:layout_width="fill_parent"
                android:layout_height="fill_parent"
                android:padding="5dp" />
        </LinearLayout>
    </TabHost>
</LinearLayout>

接下来，我们将我的活动声明为这样

public class DashboardActivity extends TabActivity {

我正在像这样构建我的标签。

private void buildTabs()
{
    Resources res = getResources(); // Resource object to get Drawables
    TabHost tabHost = (TabHost)findViewById(android.R.id.tabhost);  // The activity TabHost
    TabHost.TabSpec spec;  // Resusable TabSpec for each tab
    Intent intent;  // Reusable Intent for each tab

    // Create an Intent to launch an Activity for the tab (to be reused)
    intent = new Intent().setClass(this, StatementsActivity.class);

    // Initialize a TabSpec for each tab and add it to the TabHost
    spec = tabHost.newTabSpec("statements").setIndicator("Statements",
                      res.getDrawable(R.drawable.ic_tab_active))
                  .setContent(intent);
    tabHost.addTab(spec);

    // Do the same for the other tabs
    intent = new Intent().setClass(this, PaymentsActivity.class);
    spec = tabHost.newTabSpec("payments").setIndicator("Payments",
                      res.getDrawable(R.drawable.ic_tab_active))
                  .setContent(intent);
    tabHost.addTab(spec);

    tabHost.setCurrentTab(0);
}

当我尝试使用getTabHost(); 时，它总是返回一个空值。所以，我切换到TabHost tabHost = (TabHost)findViewById(android.R.id.tabhost);，它不会返回一个空的tabhost，但是tabHost.addTab(spec);仍然会导致一个空指针异常。

这里是堆栈跟踪

04-26 19:50:12.494: ERROR/AndroidRuntime(7367): FATAL EXCEPTION: main
04-26 19:50:12.494: ERROR/AndroidRuntime(7367): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ftni.consumer/com.ftni.consumer.ui.DashboardActivity}: java.lang.NullPointerException
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1622)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1638)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at android.app.ActivityThread.access$1500(ActivityThread.java:117)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:928)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at android.os.Handler.dispatchMessage(Handler.java:99)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at android.os.Looper.loop(Looper.java:123)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at android.app.ActivityThread.main(ActivityThread.java:3647)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at java.lang.reflect.Method.invokeNative(Native Method)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at java.lang.reflect.Method.invoke(Method.java:507)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at dalvik.system.NativeStart.main(Native Method)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367): Caused by: java.lang.NullPointerException
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at android.widget.TabHost.addTab(TabHost.java:212)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at com.ftni.consumer.ui.DashboardActivity.buildTabs(DashboardActivity.java:75)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at com.ftni.consumer.ui.DashboardActivity.onCreate(DashboardActivity.java:29)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1586)
04-26 19:50:12.494: ERROR/AndroidRuntime(7367):     ... 11 more

第 75 行是第一个 tabHost.addTab(spec);

另外，我的所有活动都在我的清单中声明。

<activity android:name=".ui.DashboardActivity"></activity>
<activity android:name=".ui.StatementsActivity"></activity>
<activity android:name=".ui.PaymentsActivity"></activity>

编辑：

为了证明这不是问题，我删除了操作栏，将布局完全按照教程中的内容进行，但我仍然得到从 getTabHost(); 返回的空值

编辑 2： 为了清楚起见，完整的类代码

public class DashboardActivity extends TabActivity {
    private ProfileModel profile;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        profile = Controller.getProfile();

        setContentView(R.layout.dashboard);

        buildTabs();

        new LoadDashboardTask().execute();
    }

    @Override
    public void onContentChanged()
    {
        ActionBar actionBar = (ActionBar)findViewById(R.id.actionbar);
        if (actionBar != null)
        {
            actionBar.setOnTitleClickListener(new OnClickListener() {
                public void onClick(View v) {
                    //do nothing for now.  User is already "home"
                }
            });

            if(profile.Accounts.length == 1)
                actionBar.setTitle(profile.Accounts[0].Name);
            else
                actionBar.setTitle(profile.Name);

        }
    }

    private void buildTabs()
    {
        Resources res = getResources(); // Resource object to get Drawables
        TabHost tabHost = getTabHost();// The activity TabHost

        if(tabHost != null)
        {
            // Initialize a TabSpec for each tab and add it to the TabHost
            TabSpec statementSpec = tabHost.newTabSpec("statements").setIndicator("Statements",
                              res.getDrawable(R.drawable.ic_tabs_statements))
                          .setContent(new Intent().setClass(DashboardActivity.this, StatementsActivity.class));
            tabHost.addTab(statementSpec);

            TabSpec paymentSpec = tabHost.newTabSpec("payments").setIndicator("Payments",
                              res.getDrawable(R.drawable.ic_tabs_payments))
                          .setContent(new Intent().setClass(DashboardActivity.this, PaymentsActivity.class));
            tabHost.addTab(paymentSpec);

            tabHost.setCurrentTab(0);
        }
    }

    private class LoadDashboardTask extends AsyncTask<Void, Void, Void> {
        @Override
        protected void onPreExecute()
        {
            ActionBar actionBar = (ActionBar)findViewById(R.id.actionbar);
            actionBar.setProgressBarVisibility(View.VISIBLE);
        }

        @Override
        protected Void doInBackground(Void... params) 
        {
            return null;
        }

        @Override
        protected void onPostExecute(Void result)
        {
            ActionBar actionBar = (ActionBar)findViewById(R.id.actionbar);
            actionBar.setProgressBarVisibility(View.GONE);
        }
    }
}

Answer 1

文档指出，如果使用 findViewById() 加载 TabHost，您应该“在添加选项卡之前调用 setup()。”，这就是您正在做的事情。见here。但是，既然您使用的是 TabActivity，为什么不调用 getTabHost() 而不是手动获取视图？