java - 重写 OnReceive 中的 Null 局部变量

Question

我在 MainActivity 的 onCreate 中初始化了接口(interface) SMSListener，但在重写的 onReceive 函数中它为 null。我是否在 onReceive 中错误地使用了公共(public)接口(interface)变量？每当我在重写函数之外测试变量时，我都会正确初始化该变量。

短信接收器:

public class SmsReceiver extends BroadcastReceiver {
    public interface OnCustomReceiveSMS {
        void OnReceiveSMS(String inNumber, String inText);
    }
    public OnCustomReceiveSMS SMSListener;

    //constructor
    public SmsReceiver(){
        this.SMSListener = null;
    }

    //register sms listener
    public void SetCustomEventListener(OnCustomReceiveSMS eventListener){
        this.SMSListener = eventListener;
        this.SMSListener.OnReceiveSMS("test1", "test2");
    }

    @Override
    public void onReceive(Context context, Intent intent) {
         //THIS IS ALWAYS FALSE EVEN AFTER INITIALIZED
         if(this.SMSListener != null){
            Toast.makeText(context, "SMSListener is NOT null", Toast.LENGTH_SHORT).show();
            this.SMSListener.OnReceiveSMS("test3", "test4");
         }else{
            Toast.makeText(context, "SMSListener is NULL", Toast.LENGTH_SHORT).show();
         }
    }
}

主要 Activity :

public class MainActivity extends AppCompatActivity {
    SmsReceiver smsReceiverObj;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //initialize SMS receiver and register event listener
        this.smsReceiverObj = new SmsReceiver();
        this.smsReceiverObj.SetCustomEventListener(new SmsReceiver.OnCustomReceiveSMS() {
            @Override
            public void OnReceiveSMS(String inNumber, String inText) {
                Toast.makeText(getApplicationContext(), "test event listener fired", Toast.LENGTH_SHORT).show();
            }
        });
   }
}

SetCustomEventListener 中的第一个测试(test1，test2)在初始化接口(interface)变量后立即正常工作。当我稍后尝试在 onReceive 函数中使用它时，我总是收到“SMSListener is NULL”调试消息。

Answer 1

问题可能是粘性广播，它会在setCustomEventListener之前调用onReceive方法，更好的方法是初始化它在构造函数中

public class SmsReceiver extends BroadcastReceiver {
    public interface OnCustomReceiveSMS {
        void OnReceiveSMS(String inNumber, String inText);
    }
    public OnCustomReceiveSMS SMSListener;

    //constructor
    public SmsReceiver(OnCustomReceiveSMS eventListener){
        this.SMSListener = eventListener;
        this.SMSListener.OnReceiveSMS("test1", "test2");
    }

    @Override
    public void onReceive(Context context, Intent intent) {
         //THIS IS ALWAYS FALSE EVEN AFTER INITIALIZED
         if(this.SMSListener != null){
            Toast.makeText(context, "SMSListener is NOT null", Toast.LENGTH_SHORT).show();
            this.SMSListener.OnReceiveSMS("test3", "test4");
         }else{
            Toast.makeText(context, "SMSListener is NULL", Toast.LENGTH_SHORT).show();
         }
    }
}

在您的 Activity 中

this.smsReceiverObj = new SmsReceiver(new SmsReceiver.OnCustomReceiveSMS() {
            @Override
            public void OnReceiveSMS(String inNumber, String inText) {
                Toast.makeText(getApplicationContext(), "test event listener fired", Toast.LENGTH_SHORT).show();
            }
        });

编辑

问题是您尝试在 Manifest 中注册它，从 list 中删除 receiver 并将其注册到 MainActivity 中，它的工作方式如下一个魅力

this.smsReceiverObj = new SmsReceiver(new SmsReceiver.OnCustomReceiveSMS() {
                @Override
                public void OnReceiveSMS(String inNumber, String inText) {
                    Toast.makeText(getApplicationContext(), "test event listener fired", Toast.LENGTH_SHORT).show();
                }
            });
registerReceiver(this.smsReceiverObj,new IntentFilter());