android studio 上的微调器

Question

its a very simple code yet it cant run

ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this,R.array.Categories, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
itemCat.setAdapter(adapter);

Ive named my spinner itemCat, array as Categories and adapter as adapter.

Process: com.example.myapplication, PID: 3716 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myapplication/com.example.myapplication.item_register}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)' on a null object reference

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)' on a null object reference

Answer 1

You have to first create the view then call the methods.

Secondly, the spinner should be created under the onCreate() .

Answer 2

某些东西是空的，导致这次崩溃。我猜你的 itemCat 是空的，你没有创建它。