Java Android : Subclass, 从主 Activity 类调用方法导致 NullPointerException

Question

我想从子类调用函数到主 Activity 类。 这是我的源代码: 短信.java

public class SMS extends ListActivity {
    public void testerr(String kata) {
        Toast.makeText(getBaseContext(), "test coyyyy="+kata, Toast.LENGTH_LONG).show();
    }
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        }
}

SMSReceiver.java

public class SmsReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Bundle bundle = intent.getExtras();
        SmsMessage[] msgs = null;
        String str = "";
        try {
            if (bundle != null) {
                Object[] pdus = (Object[]) bundle.get("pdus");
                msgs = new SmsMessage[pdus.length];
                for (int i = 0; i < msgs.length; i++) {
                    msgs[i] = SmsMessage.createFromPdu((byte[]) pdus[i]);
                    str += "SMS from " + msgs[i].getOriginatingAddress();
                    str += " :";
                    str += msgs[i].getMessageBody().toString();
                    str += "\n";
                }
                Toast.makeText(context, str, Toast.LENGTH_LONG).show();
                SMS sss = new SMS(); ---> call the main class
                sss.testerr("try the words"); ---> call method from main class
                Toast.makeText(context, str, Toast.LENGTH_LONG).show();
            }
        }
        catch(NullPointerException ex){
            Toast.makeText(context, "penyakite neng kene:"+ex.getMessage(), Toast.LENGTH_LONG).show();
        }
    }
}

我的程序在收到新短信后运行，并且在调用 sss.testerr("my examplewords"); 时总是得到 NullPointerException; 有什么线索吗？ 非常感谢您的帮助

Answer 1

您不应该使用 Activity 的构造函数来实例化 Activity，或者以 Intent 启动它，或者如果 Activity 已经启动，则使其实现广播接收器。

如果您只想显示接收器中的 toast，则可以使用 this question 的答案