method ‘void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)‘ on a null object refe

Posted 2021-06-29 闲言_

异常产生环境

在android 使用dialog 引入Spinner 控件时产生异常

异常描述

     Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Method.invoke(Native Method)
        at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:397)
        at android.view.View.performClick(View.java:5637) 
        at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:967) 
        at android.view.View$PerformClick.run(View.java:22429) 
        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:6119) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)' on a null object reference
        at cn.bloghut.StudentList.add(StudentList.java:122)
        at java.lang.reflect.Method.invoke(Native Method) 
        at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:397) 
        at android.view.View.performClick(View.java:5637) 
        at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:967) 
        at android.view.View$PerformClick.run(View.java:22429) 
        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:6119) 
        at java.lang.reflect.Method.invoke(Native Method) 

异常原因

• 因为我把Spinner 嵌在dialog 里面了，获取Spinner 的使用使用findViewById(R.id.spinner); 肯定是获取不到的。
• 正确的获取代码

view.findViewById(R.id.spinner);

• 代码调式如下：
• 奇怪的是sprinner 为空，用一个null 调用setAdapter 方法，却不报空指针异常而是 onClick(AppCompatViewInflater 异常
  

解决办法

• 修改获取控件的代码即可

spinner = (Spinner) view.findViewById(R.id.spinner);