android - 我在应用程序中添加了一个微调器，但由于适配器代码， Activity 没有启动

Question

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.rishabh.casino/com.example.rishabh.casino.Game}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)' on a null object reference
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2314)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2388)
            at android.app.ActivityThread.access$800(ActivityThread.java:148)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1292)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5312)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)
     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

主要问题是您正在 View 上方初始化微调器。你应该放 setContentView(R.layout.activity_game);在上面和之后你应该初始化其他组件。更正您的 onCreate

@Override
                protected void onCreate(Bundle savedInstanceState) {
                   super.onCreate(savedInstanceState);
             setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
                    setContentView(R.layout.activity_game); //Initialize layout first

                    spin=(Spinner)findViewById(R.id.spinner);
                    rembal=(TextView)findViewById(R.id.textView8);
                    bet_amount=(TextView)findViewById(R.id.textView9);
                    beton=(TextView)findViewById(R.id.textView10);
                    result=(TextView)findViewById(R.id.textView11);
                    bet=(EditText)findViewById(R.id.editText2);
                    okgen=(Button)findViewById(R.id.button4);

                    ArrayAdapter<String> adapter_option=new ArrayAdapter<String>(this,android.R.layout.simple_spinner_item,options);
                    adapter_option.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
                    spin.setAdapter(adapter_option);
                    spin.setOnItemSelectedListener(this);
                    super.onCreate(savedInstanceState);

                    if (savedInstanceState == null) {
                        getSupportFragmentManager().beginTransaction()
                                .add(R.id.container, new PlaceholderFragment())
                                .commit();
                    }
                }

这就是空指针异常背后的原因。 View 尚未初始化，您正在尝试初始化 View 内的微调器。