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。
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
最佳答案
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。
@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
关于Android NullPointerException - Spinner onItemSelected `view` 旋转后参数为空，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/33747884/