getLineStart（）總是爲我的TextView返回null？

Question

我有一個TextView，我想得到一些特定的行文本，但是當我使用txt.getLayout.getLineStart(1)時，它返回null並崩潰應用程序，原因是什麼？

TextView txt = (TextView)mRootView.findViewById(R.id.txt); 
int start = txt.getLayout().getLineStart(1); 
int end = txt.getLayout().getLineEnd(1); 
String first = txt.getText().subSequence(start,end).toString(); 

崩潰日誌

E/AndroidRuntime: FATAL EXCEPTION: main 
        Process: com.sattva.animalsencyclopedia, PID: 11244 
        java.lang.NullPointerException 
         at com.sattva.animalsencyclopedia.fragments.FragmentInformation.onViewCreated(FragmentInformation.java:110) 
         at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1086) 
         at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1252) 
         at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738) 
         at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1617) 
         at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517) 
         at android.os.Handler.handleCallback(Handler.java:808) 
         at android.os.Handler.dispatchMessage(Handler.java:103) 
         at android.os.Looper.loop(Looper.java:193) 
         at android.app.ActivityThread.main(ActivityThread.java:5333) 
         at java.lang.reflect.Method.invokeNative(Native Method) 
         at java.lang.reflect.Method.invoke(Method.java:515) 
         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:829) 
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:645) 
         at dalvik.system.NativeStart.main(Native Method) 

Answer 1

也許你沒發現用正確的方式方法findViewById()這一觀點。你正在使用片段，可能你有類似getActivity().findViewById()。嘗試在你的onCreateView()方法做這樣的事情view.findViewById()，其中view是膨脹的結果。

As @pskink從文檔中提到：returns Layout the Layout that is currently being used to display the text. This can be null if the text or width has recently changes.嘗試在onStart或onCreate方法中調用此代碼，但應該將txt作爲類成員變量。與logcat的

int start = txt.getLayout().getLineStart(1); 
int end = txt.getLayout().getLineEnd(1); 
String first = txt.getText().subSequence(start,end).toString();