如何修复java.lang.ArrayIndexOutOfBoundsException？

Question

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.calculatorcd2, PID: 8722
    java.lang.IndexOutOfBoundsException: setSpan (2 ... 2) ends beyond length 1
        at android.text.SpannableStringBuilder.checkRange(SpannableStringBuilder.java:1265)
        at android.text.SpannableStringBuilder.setSpan(SpannableStringBuilder.java:684)
        at android.text.SpannableStringBuilder.setSpan(SpannableStringBuilder.java:677)
        at android.text.Selection.setSelection(Selection.java:76)
        at android.text.Selection.setSelection(Selection.java:87)
        at android.widget.EditText.setSelection(EditText.java:103)
        at com.example.calculatorcd2.MainActivity.addText1(MainActivity.java:1343)
        at com.example.calculatorcd2.MainActivity$30.onClick(MainActivity.java:535)
        at android.view.View.performClick(View.java:5610)
        at android.view.View$PerformClick.run(View.java:22265)
        at android.os.Handler.handleCallback(Handler.java:751)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6077)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
Application terminated.