android - 从 Android 中的 strings.xml 加载时出现空指针异常

Question

由于某种原因，我收到一个空指针异常。尝试从字符串 xml 文件加载字符串时，我的应用程序崩溃。我不知道为什么会有一个空指针。有任何想法吗？谢谢!

Quiz.java fragment :

  String[] questions = {getString(R.string.q1),
            getString(R.string.q2),
            getString(R.string.q3),
            getString(R.string.q4),
            getString(R.string.q5),getString(R.string.q6),
            getString(R.string.q7),
            getString(R.string.q8),
            getString(R.string.q9),
            getString(R.string.q10),


    };   

字符串.xml:

<resources>
        <string name="app_name">Beatles Quiz</string>
        <string name="q1">What year did John say the Beatles were more popular than Jesus?</string>
        <string name="q2">What did the Beatles receive for performing three times on The Ed Sullivan Show?</string>
        <string name="q3">Who sent a congratulatory telegram to the Beatles before that first performance?</string>
        <string name="q4">Which song starts "It was 20 years ago today …"?"</string>
        <string name="q5">Who was the Beatles\' original drummer?</string>
        <string name="q6">Which song starts "When I find myself in times of trouble …"?</string>
        <string name="q7">Which pair of Beatles first played together in a band?"</string>
        <string name="q8">Which song starts: "I think I\'m gonna be sad …"?</string>
        <string name="q9">Who was the youngest Beatle?"</string>
        <string name="q10">Which song starts: "Well, she was just 17 …"?"</string>

        <string name="q11">Besides Liverpool, where did the Beatles perform regularly in the early 1960s?</string>
        <string name="q12">Which song starts: "There are places I remember …"?</string>
        <string name="q13">Which album cover features 73 people?"</string>
        <string name="q14">Which song starts: "Try to see it my way …"?"</string>
        <string name="q15">What\'s the official name of the album best known as "The White Album"?</string>
        <string name="q16">Which song starts: "In the town where I was born …"?</string>
        <string name="q17">Who was the first Beatle to get married?</string>
        <string name="q18">Which song starts: "What would you do if I sang out of tune …"?</string>
        <string name="q19">The Beatles got their MBEs in 1965. Which of them later returned his?</string>
        <string name="q20">What was the last Beatles studio album to be recorded, though it was not the last one released?</string>

        <string name="q21">What do the songs "Drive My Car," "Taxman," "Back in the USSR" and "Come Together" have in common?</string>
        <string name="q22">Which song includes the lyric "Man, you should have seen them kicking Edgar Allan Poe"?</string>
        <string name="q23">Which Broadway show tune did the Beatles cover in their early days?</string>
        <string name="q24">The working title of "Yesterday" was:</string>
        <string name="q25">Which was the last Beatles album to be released?</string>
        <string name="q26">Which ex-Beatle had the first No. 1 hit single on the Billboard Hot 100?</string>
        <string name="q27">What was the working title of the film "Help!"?"</string>
        <string name="q28">Which was the first song Ringo alone wrote for the Beatles?</string>
        <string name="q29">What year did the Beatles stop touring?</string>
        <string name="q30">Frank Sinatra considered this Beatles song (which he also performed repeatedly in concert)"the greatest love song of the past 50 years":</string>

        <string name="q31">For whom did Paul McCartney write "Hey Jude"?</string>
        <string name="q32">Which Beatle is barefoot on the Abbey Road cover?</string>
        <string name="q33">Who does not appear on the cover of Sgt. Pepper\'s Lonely Hearts Club Band?</string>
        <string name="q34">Which song includes the lyric "Everywhere, people stare"?"</string>
        <string name="q35">Which song was NOT on the setlist during the Beatles’ Ed Sullivan show appearance?</string>
        <string name="q36">The album "Please Please Me" contains the first Beatles song featuring George Harrison on lead vocals. Which song was it?</string>
        <string name="q37">Which Beatle is the only one to have been knighted?</string>
        <string name="q38">The album "Rubber Soul" features the first song where credit was given to Ringo Starr as a co-songwriter. Which song did Ringo lend his efforts to?</string>
        <string name="q39">Which Beatles song contains the lyrics "By making his world a little colder"</string>
        <string name="q40">Which Beatles song contains the lyrics "Nobody knows, just we two"?"</string>

         <string name="q41">Which song from Let It Be was actually one of the earliest Lennon/McCartney compositions?</string>
         <string name="q42">Which song includes the lyric "The farther one travels, the less one knows"?"</string>
        <string name="q43">Which John Lennon track combined two takes in two different keys?</string>
        <string name="q44">Which song includes the lyric "Drove from Paris to the Amsterdam Hilton"?"</string>
        <string name="q45">The Revolver track “For No One” features a solo on what instrument?</string>
        <string name="q46">Which song includes the lyric "I got something to say that might cause you pain"?"</string>
        <string name="q47">Who is "I’m Looking Through You" about?"</string>
        <string name="q48">Which song includes the lyric "Everybody had a great year, everybody let their hair down"?"</string>
        <string name="q49">Who plays bass on "The Long and Winding Road"?"</string>
        <string name="q50">Which song includes the lyric "The teachers who taught me weren\'t cool"?"</string>
    </resources>

错误信息:

05-11 23:23:06.652 26077-26077/tuxstudios.com.beatlesquiz E/AndroidRuntime: FATAL EXCEPTION: main Process: tuxstudios.com.beatlesquiz, PID: 26077 java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{tuxstudios.com.beatlesquiz/tuxstudios.com.beatlesquiz.QuizActivity2}: java.lang.NullPointerException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2321) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2507) at android.app.ActivityThread.access$900(ActivityThread.java:172) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:146) at android.app.ActivityThread.main(ActivityThread.java:5692) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:515) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1291) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107) at dalvik.system.NativeStart.main(Native Method) Caused by: java.lang.NullPointerException at android.content.ContextWrapper.getResources(ContextWrapper.java:94) at android.view.ContextThemeWrapper.getResources(ContextThemeWrapper.java:78) at android.content.Context.getString(Context.java:363) at tuxstudios.com.beatlesquiz.QuizActivity2.(QuizActivity2.java:32) at java.lang.Class.newInstanceImpl(Native Method) at java.lang.Class.newInstance(Class.java:1208) at android.app.Instrumentation.newActivity(Instrumentation.java:1067) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2312) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2507)  at android.app.ActivityThread.access$900(ActivityThread.java:172)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308)  at android.os.Handler.dispatchMessage(Handler.java:102)  at android.os.Looper.loop(Looper.java:146)  at android.app.ActivityThread.main(ActivityThread.java:5692)  at java.lang.reflect.Method.invokeNative(Native Method)  at java.lang.reflect.Method.invoke(Method.java:515)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1291)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107)  at dalvik.system.NativeStart.main(Native Method)

Answer 1

你应该使用

int [] stringIds = { R.string.q1, R.string.q2... }

当你 声明 字符串 []，您调用 getString(id)，其中需要一些上下文或资源，但 尚未初始化 ，这说明了空错误。

例如

getResources().getString(R.string.q1); //here getResources() may be null.

然后在创建上下文(例如 Activity )后，调用下面的函数

for( int id : stringIds)
    String question = getResources().getString(id); //now this is no longer null

不同之处在于 R.string.q1 始终可访问，无论是在编译时还是在运行时。

希望这可以帮助。