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我試圖通過應用程序從網站獲取數據到我的手機! 所以我嘗試了使用AsyncTask的jsoup,以避免在主線程上使用網絡。 好了,但我的應用程序甚至不會啓動。它說,錯誤是空指針異常 下面是代碼和logcat的片段Android應用程序在使用jsoup和AsyncTask時崩潰(實際上甚至沒有啓動)
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mt= new MyTask();
mt.execute(URL);
mytext =(TextView)findViewById(R.id.mytext);
}
class MyTask extends AsyncTask<String, Void, String>{
Document doc;
String abouttext;
@Override
protected void onPreExecute(){
super.onPreExecute();
mytext.setText("please wait...");
}
protected String doInBackground(String...params){
String url=params[0];
Document doc;
try{
doc = Jsoup.connect(url).get();
Element about = doc.select("div.box-content").first();
String abouttext = about.text();
}
catch(Exception e){
e.printStackTrace();
}
return abouttext;
}
protected void onPostExecute(String result){
super.onPostExecute(result);
mytext.setText(result);
}
}
,這裏是日誌
09-21 18:50:36.746: E/Trace(778): error opening trace file: No such file or directory (2)
09-21 18:50:37.445: D/AndroidRuntime(778): Shutting down VM
09-21 18:50:37.445: W/dalvikvm(778): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
09-21 18:50:37.506: E/AndroidRuntime(778): FATAL EXCEPTION: main
09-21 18:50:37.506: E/AndroidRuntime(778): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.web/com.example.web.MainActivity}: java.lang.NullPointerException
09-21 18:50:37.506: E/AndroidRuntime(778): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
09-21 18:50:37.506: E/AndroidRuntime(778): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
PLS有人告訴我有什麼做錯了! 謝謝!
我會後整個日誌我猜
09-21 19:52:34.164: D/AndroidRuntime(796): Shutting down VM
09-21 19:52:34.194: W/dalvikvm(796): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
09-21 19:52:34.244: E/AndroidRuntime(796): FATAL EXCEPTION: main
09-21 19:52:34.244: E/AndroidRuntime(796): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.web/com.example.web.MainActivity}: java.lang.NullPointerException
09-21 19:52:34.244: E/AndroidRuntime(796): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
09-21 19:52:34.244: E/AndroidRuntime(796): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
09-21 19:52:34.244: E/AndroidRuntime(796): at android.app.ActivityThread.access$600(ActivityThread.java:141)
09-21 19:52:34.244: E/AndroidRuntime(796): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
09-21 19:52:34.244: E/AndroidRuntime(796): at android.os.Handler.dispatchMessage(Handler.java:99)
09-21 19:52:34.244: E/AndroidRuntime(796): at android.os.Looper.loop(Looper.java:137)
09-21 19:52:34.244: E/AndroidRuntime(796): at android.app.ActivityThread.main(ActivityThread.java:5041)
09-21 19:52:34.244: E/AndroidRuntime(796): at java.lang.reflect.Method.invokeNative(Native Method)
09-21 19:52:34.244: E/AndroidRuntime(796): at java.lang.reflect.Method.invoke(Method.java:511)
09-21 19:52:34.244: E/AndroidRuntime(796): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
09-21 19:52:34.244: E/AndroidRuntime(796): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
09-21 19:52:34.244: E/AndroidRuntime(796): at dalvik.system.NativeStart.main(Native Method)
09-21 19:52:34.244: E/AndroidRuntime(796): Caused by: java.lang.NullPointerException
09-21 19:52:34.244: E/AndroidRuntime(796): at com.example.web.MainActivity$MyTask.onPreExecute(MainActivity.java:37)
09-21 19:52:34.244: E/AndroidRuntime(796): at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586)
09-21 19:52:34.244: E/AndroidRuntime(796): at android.os.AsyncTask.execute(AsyncTask.java:534)
09-21 19:52:34.244: E/AndroidRuntime(796): at com.example.web.MainActivity.onCreate(MainActivity.java:27)
09-21 19:52:34.244: E/AndroidRuntime(796): at android.app.Activity.performCreate(Activity.java:5104)
09-21 19:52:34.244: E/AndroidRuntime(796): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
09-21 19:52:34.244: E/AndroidRuntime(796): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
09-21 19:52:34.244: E/AndroidRuntime(796): ... 11 more
不行,不行!我確實喜歡你說刪除了doc的第二個聲明,然後初始化關於text到HI,然後在下一行寫了「abouttext = about.text();」但它顯示了相同的錯誤nullpointerException。還有其他建議嗎?還有一個人現在認爲錯誤指針是它顯示的行已經改變並且指向mt.execute(URL); 09-21 19:18:53.447:E/AndroidRuntime(790):\t在com.example.web.MainActivity.onCreate(MainActivity.java:27) 這是mt.execute(url) – user2802715
之前設置「abouttext = about.text();」 ()是否爲空... if(about.text()。toString()!= null){abouttext = about.text();} else {abouttext =「Text Not set」 ;} –
不,我不喜歡!怎麼做? – user2802715