Android NullPointerException - Spinner onItemSelected `view` 旋转后参数为空

Question

注意:来自 another, similar SO question's answer 的限制解决方法为我工作，但我有兴趣找到真正的解决方案。解决方法是将其添加到我的 Activity 中:

@Override  
protected void onSaveInstanceState(Bundle outState) { /* do nothing */ }

但我仍然想留下这个问题，希望找到更好的解决方案。

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我的应用程序在最新的 Android(Marshmallow、Lollipop)上旋转时崩溃，但它在 KitKat 上运行。在 Spinner onClick 方法中，我得到了父项的第一个子项，它是下拉列表中的第一个 TextView (又名微调器)。当我不旋转它时它工作得很好。此外，当我注释掉抛出 NullPointerException 的那一行时，它也能正常工作。所以这是问题的唯一原因。

我知道它是 Null，但我不明白为什么，或者如何解决它？另外请注意，我不能为此使用 XML，因为文本颜色只能在运行时动态知道。另外，我希望最小 API 为 15。

我添加了一些调试代码，发现在旋转之前，parent 和view 参数都不为空。但是旋转后，view 为空。 (但是 parent 仍然不为空)。

查看出现空指针异常的行******:

private void setUpSpinner(int accentColor, final int backgroundColor, Toolbar toolbar)
{
    Spinner spinner = (Spinner) findViewById(R.id.spinner);

    //Get rid of the normal toolbar's title, because the spinner is replacing the title.
    getSupportActionBar().setDisplayShowTitleEnabled(false);

    //Set the choices on the spinner by setting the adapter.
    spinner.setAdapter(new SpinnerAdapter(toolbar.getContext(), new String[]{"Overview", "Story", "Specifications", "Poll", "Video"},
            accentColor, backgroundColor));

    //Set the listener for when each option is clicked.
    spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener()
    {

        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id)
        {
            Log.e("ITEM SELECTED", "SPINNER" + Integer.toString(position));

            //This is necessary to set the color of the "action bar title." (Really, this is just
            //changing the text color of the spinner when it is at rest; or changing the selected
            //option's color.)
 ****************((TextView) view).setTextColor(backgroundColor);

            //Change the contents of the DealPage depending on what option was selected in the spinner.
           // CODE OMITTED
        }

        @Override
        public void onNothingSelected(AdapterView<?> parent)
        {
        }
    });
}

spinner_item.xml:

<TextView xmlns:android="http://schemas.android.com/apk/res/android"
          android:id="@android:id/text1"
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:textAppearance="?android:attr/textAppearanceListItemSmall"
          android:gravity="center_vertical"
          android:padding="5dp"
          android:minHeight="?android:attr/listPreferredItemHeightSmall"/>

OnCreate 方法:

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        context = this;
        RealmDatabase.setRealmInstance(this);

        //----------- UNPACK EXTRAS -----------
        String date = getIntent().getExtras().getString(KeyStrings.EXTRA_DATE);

        //---------------- PREREQUISITE INITIALIZATION ----------
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_deal_page);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar_with_spinner);
        setSupportActionBar(toolbar);

        //------------ Enable "UP" navigation ---------------
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        getDataFromDatabase(date);

        //----------------- THEMES AND COLORS ------------------

        //Set up colors
        final int backgroundColor = this.deal.getTheme().getBackgroundColor().getColor();
        final int accentColor = this.deal.getTheme().getAccentColor().getColor();
        String themeForeground = this.deal.getTheme().getForeground();
        final int foreground = generateForegroundColor(themeForeground);
        final String foregroundWebView = generateForegroundWebViewString(themeForeground); // This is necessary because HTML does not have an alpha channel.

        //Set toolbar colors
        toolbar.setBackgroundColor(accentColor);
        toolbar.setTitleTextColor(backgroundColor);

        //Set Page Background Color
        RelativeLayout dealPageBackground = (RelativeLayout) findViewById(R.id.deal_page_background);
        dealPageBackground.setBackgroundColor(backgroundColor);

        //----------- INITIALIZE THE ACTUAL DEAL PAGE STUFF ----------------

        //Title
        TextView title = (TextView) findViewById(R.id.title);
        title.setText(this.deal.getTitle());
        title.setTextColor(foreground);

        //Price
        TextView price = (TextView) findViewById(R.id.price);
        NumberFormat fmt = NumberFormat.getCurrencyInstance();
        price.setText(fmt.format(this.deal.getItems().first().getPrice()));
        price.setTextColor(foreground);

        //ViewInBrowser
        setUpViewInBrowserButton(backgroundColor, accentColor);

        AndDown andDown = new AndDown();

        //Set up "linkColorHTML"
        String linkColorHTML = generateLinkColorHTML(accentColor);

        //Features
        setUpFeaturesView(andDown, backgroundColor, linkColorHTML, foregroundWebView);

        //More Specs button
        setUpMoreSpecsButton(backgroundColor, foreground, (Spinner) findViewById(R.id.spinner));

        //Story Title
        TextView storyTitle = (TextView) findViewById(R.id.story_title);
        storyTitle.setText(this.deal.getStory().getTitle());
        storyTitle.setTextColor(accentColor);

        //Story Body
        setUpStoryBody(andDown, backgroundColor, linkColorHTML, foregroundWebView);

        //Specs Title
        TextView specsTitle = (TextView) findViewById(R.id.specs_title);
        specsTitle.setText(this.deal.getTitle());
        specsTitle.setTextColor(accentColor);

        //Specs
        setUpSpecificationsView(andDown, backgroundColor, linkColorHTML, foregroundWebView);

        //Set up ViewPager
        ViewPager viewPager = (ViewPager) findViewById(R.id.photos_view_pager);
        viewPager.setAdapter(new PhotoPagerAdapter(this, this.deal.getPhotos()));

        //Set up spinner
        setUpSpinner(accentColor, backgroundColor, toolbar);

        //Set up poll title
        TextView pollTitle = (TextView) findViewById(R.id.poll_title);
        pollTitle.setText(this.poll.getTitle());
        pollTitle.setTextColor(accentColor);

        //Set up poll view-forum-topic-in-browser button
        setUpViewForumTopicInBrowserButton(backgroundColor, accentColor);

        //Set up poll
        setUpPoll(foreground, accentColor);

        //Set up video title
        TextView videoTitle = (TextView) findViewById(R.id.video_title);
        videoTitle.setText(this.video.getTitle());
        videoTitle.setTextColor(accentColor);

        //Set up video view-forum-topic-in-browser button
        setUpViewVideoForumTopicInBrowserButton(backgroundColor, accentColor);

        //Set up youtube video
        setUpYoutubeVideo();


    }

日志:

11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime: FATAL EXCEPTION: main
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime: Process: com.example.meh, PID: 6507
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setTextColor(int)' on a null object reference
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at com.example.meh.Deal.DealPage$6.onItemSelected(DealPage.java:480)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.AdapterView.fireOnSelected(AdapterView.java:897)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.AdapterView.selectionChanged(AdapterView.java:884)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.AdapterView.checkSelectionChanged(AdapterView.java:1047)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.AdapterView.handleDataChanged(AdapterView.java:1027)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.AbsSpinner.onMeasure(AbsSpinner.java:184)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.Spinner.onMeasure(Spinner.java:507)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.support.v7.widget.AppCompatSpinner.onMeasure(AppCompatSpinner.java:410)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.View.measure(View.java:17430)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.support.v7.widget.Toolbar.measureChildCollapseMargins(Toolbar.java:1225)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.support.v7.widget.Toolbar.onMeasure(Toolbar.java:1333)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.View.measure(View.java:17430)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.View.measure(View.java:17430)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.support.v7.internal.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:124)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.View.measure(View.java:17430)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.View.measure(View.java:17430)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.View.measure(View.java:17430)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.View.measure(View.java:17430)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2560)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.View.measure(View.java:17430)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2001)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1767)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.Choreographer.doCallbacks(Choreographer.java:580)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.Choreographer.doFrame(Choreographer.java:550)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.os.Handler.handleCallback(Handler.java:739)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:95)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.os.Looper.loop(Looper.java:135)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:5221)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Native Method)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at java.lang.reflect.Method.invoke(Method.java:372)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
11-16 18:06:45.879 6507-6507/com.example.meh E/AndroidRuntime:     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)f

Answer 1

public void onItemSelected(AdapterView<?> parent, View view, int position, long id)

adapterView 是对 Spinner 的引用，而不是您单击的项目，您应该改为转换“view”参数。

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@李岩旋转后布局会刷新，你应该在一些回调函数中重新设置微调器，比如 onConfigurationChanged(Configuration newConfig)， Android listview disappears after screen rotation