安卓空指针异常 - 旋转后Spinner onItemSelected `view` 参数为null

Question

注意：另一个类似的Stack Overflow问题答案提供的解决方法对我有用，但是我还是想找到一个真正解决问题的方法。

该临时解决方法是在我的Activity中添加以下内容：

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

但我仍然希望保留这个问题，以便找到更好的解决方案。

---

我的应用程序在最新的Android（Marshmallow、Lollipop）上旋转时崩溃，但在KitKat上可以正常工作。在Spinner onClick方法中，我获取父级的第一个子元素，也就是下拉列表中的第一个textview（也称为spinner）。当我不旋转它时，它运行得非常好。此外，当我注释掉引发空指针异常的那行代码时，它也可以正常工作。因此，这是唯一的问题原因。

我知道它是Null，但我不明白原因以及如何解决？另外，请注意，我无法使用XML，因为文本颜色只在运行时动态确定。此外，我希望最小API为15。

我添加了一些调试代码，并发现在旋转之前，parent和view参数都不是null。但在旋转后，view为null。（但parent仍然不是null）。

请参考******处具有空指针异常的代码行：

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

- Rock Lee

Answer 1

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

adapterView是引用Spinner，而不是您点击的项目，您应该转换“view”参数。

---

@Rock Lee 旋转后，布局会被刷新，您应该在一些回调函数中重新设置旋转器，例如onConfigurationChanged(Configuration newConfig)， Android屏幕旋转后ListView消失

- shiro

---

我把代码改成那样了，但是还是出现了同样的错误。 - Rock Lee

Answer 2

您可以使用覆盖方法 onSaveInstanceState() 和 onRestoreInstanceState()。或者，要防止屏幕旋转时调用 onCreate()，只需在您的清单 XML 中添加此行 android:configChanges="keyboardHidden|orientation"

请注意：您的自定义类必须实现 Parcelable，例如下面的示例。

@Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putParcelable("obj", myClass);
    }

@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
 // TODO Auto-generated method stub
 super.onRestoreInstanceState(savedInstanceState);
 myClass=savedInstanceState.getParcelable("obj"));
}

public class MyClass implements Parcelable {
     private int mData;

 public int describeContents() {
     return 0;
 }

 /** save object in parcel */
 public void writeToParcel(Parcel out, int flags) {
     out.writeInt(mData);
 }

 public static final Parcelable.Creator<MyParcelable> CREATOR
         = new Parcelable.Creator<MyParcelable>() {
     public MyParcelable createFromParcel(Parcel in) {
         return new MyParcelable(in);
     }

     public MyParcelable[] newArray(int size) {
         return new MyParcelable[size];
     }
 };

 /** recreate object from parcel */
 private MyParcelable(Parcel in) {
     mData = in.readInt();
 }


}

- Askarc Ali

---

谢谢。它可以工作，但根据这个SO答案，它可能仍会导致其他问题：https://dev59.com/z2sz5IYBdhLWcg3wj4gc#7990543 - Rock Lee

是的，他是正确的。这不会引起其他问题。他的意思是，如果你想在旋转时处理任何东西，就不应该使用它，否则你可以使用它。如果你想编程地忽略它，可以使用onConfigurationChanged。 - Askarc Ali

我确实希望能够处理旋转方面的事情。 - Rock Lee