Android Studio（导航抽屉）开关盒“ 0”导致“错误夸大类片段”

Question

我是android开发的新手，我最近开始写应用程序，只是为了好玩。 我使用了“导航抽屉模板”。

在我的导航抽屉中，有8个元素，选择元素2-8可以正常工作。 但是，当我将动作分配给元素1时，出现“二进制xml第22行：错误放大类片段”。

我知道我编程的方式可能很奇怪，但是我以前从未编码过Java，只有C ++ ...

这很好用：

private void selectItem(int position) {
    mCurrentSelectedPosition = position;
    switch (position){
       /* case 0:
            activity_main.webview.loadUrl("http://www.random.org/");
            break;*/
        case 1:
            activity_main.webview.loadUrl("http://www.google.com/");
            break;
        case 2:
            activity_main.webview.loadUrl("http://facebook.com/");
            break;
        case 3:
            activity_main.webview.loadUrl("http://stackoverflow.com/");
            break;
        case 4:
            activity_main.webview.loadUrl("http://plus.google.com/");
            break;
        case 5:
            activity_main.webview.loadUrl("http://flickr.com/");
            break;
        case 6:
            activity_main.webview.loadUrl("http://9gag.com/");
            break;
        case 7:
            activity_main.webview.loadUrl("http://reddit.com");
            break;
    }
    if (mDrawerListView != null) {
        mDrawerListView.setItemChecked(position, true);
    }
    if (mDrawerLayout != null) {
        mDrawerLayout.closeDrawer(mFragmentContainerView);
    }
    if (mCallbacks != null) {
        mCallbacks.onNavigationDrawerItemSelected(position);
    }
}

但是，当我取消注释“ case 0”语句时，出现以下错误：

03-17 13:37:58.900    4265-4265/com.mycompany.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.mycompany.app, PID: 4265
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mycompany.app/com.mycompany.app.activity_main}: android.view.InflateException: Binary XML file line #11: Error inflating class fragment
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2329)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2391)
            at android.app.ActivityThread.access$900(ActivityThread.java:147)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1296)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5256)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:898)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)
     Caused by: android.view.InflateException: Binary XML file line #22: Error inflating class fragment
            at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:763)
            at android.view.LayoutInflater.rInflate(LayoutInflater.java:806)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:504)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:414)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:365)
            at android.support.v7.app.ActionBarActivityDelegateBase.setContentView(ActionBarActivityDelegateBase.java:240)
            at android.support.v7.app.ActionBarActivity.setContentView(ActionBarActivity.java:102)
            at com.mycompany.app.activity_main.onCreate(activity_main.java:41)
            at android.app.Activity.performCreate(Activity.java:5933)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2282)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2391)
            at android.app.ActivityThread.access$900(ActivityThread.java:147)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1296)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5256)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:898)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.webkit.WebView.loadUrl(java.lang.String)' on a null object reference
            at com.mycompany.app.NavigationDrawerFragment.selectItem(NavigationDrawerFragment.java:201)
            at com.mycompany.app.NavigationDrawerFragment.onCreate(NavigationDrawerFragment.java:80)
            at android.support.v4.app.Fragment.performCreate(Fragment.java:1763)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:915)
            at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1114)
            at android.support.v4.app.FragmentManagerImpl.addFragment(FragmentManager.java:1216)
            at android.support.v4.app.FragmentManagerImpl.onCreateView(FragmentManager.java:2169)
            at android.support.v4.app.FragmentActivity.onCreateView(FragmentActivity.java:297)
            at android.support.v7.app.ActionBarActivity.onCreateView(ActionBarActivity.java:543)
            at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:727)
            at android.view.LayoutInflater.rInflate(LayoutInflater.java:806)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:504)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:414)
            at android.view.LayoutInflater.inflate(LayoutInflater.java:365)
            at android.support.v7.app.ActionBarActivityDelegateBase.setContentView(ActionBarActivityDelegateBase.java:240)
            at android.support.v7.app.ActionBarActivity.setContentView(ActionBarActivity.java:102)
            at com.mycompany.app.activity_main.onCreate(activity_main.java:41)
            at android.app.Activity.performCreate(Activity.java:5933)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2282)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2391)
            at android.app.ActivityThread.access$900(ActivityThread.java:147)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1296)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5256)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:898)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:693)

我看到它会导致nullpointer-exception，但我不明白为什么...所以也许您可以看一下，让我知道是否需要更多代码=）

在此先感谢，fl0_at

- -编辑 - -

这是您请求的xml：

<android.support.v4.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:id="@+id/drawer_layout"
    android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".NMW">
    <FrameLayout android:id="@+id/container" android:layout_width="match_parent"
        android:layout_height="match_parent" />
    <WebView
        android:id="@+id/webview"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        />
    <fragment android:id="@+id/navigation_drawer"
        android:layout_width="@dimen/navigation_drawer_width" android:layout_height="match_parent"
        android:layout_gravity="start"
        class="com.mycompany.app.NavigationDrawerFragment"
        tools:layout="@layout/fragment_navigation_drawer"
        android:background="@drawable/activated_background"/>
</android.support.v4.widget.DrawerLayout>

Answer 1

感谢Ivo Beckers和Selvin，我找到了解决问题的方法。 在我的NavigationDrawerFragment.java中 ，我在onCreate和

if(activity_main.webview != null){
    selectItem(0);
}

所以onCreate的最终版本是：

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

    SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(getActivity());
    mUserLearnedDrawer = sp.getBoolean(PREF_USER_LEARNED_DRAWER, false);

    if (savedInstanceState != null) {
        mCurrentSelectedPosition = savedInstanceState.getInt(STATE_SELECTED_POSITION);
        mFromSavedInstanceState = true;
    }

    // Select either the default item (0) or the last selected item, i.e. selectItem(mCurrentSelectedPosition);
    if (activity_main.webview != null) {
        selectItem(0);
    }
}

干杯!

fl0_at