java - 我的界面触发时得到 NullPointerException

Question

我尝试了 Toast 消息界面。如果应用程序未连接互联网，我想显示一条Toast消息并且我想要java接口(interface)。

这是MotherActivity.java。此文件实现 ToastMessagges.ToastMessaggeCallback

   public class MotherActivity extends ActionBarActivity implements ToastMessagges.ToastMessaggeCallback {

        ToastMessagges toastMessagges;

        @Override
        protected void onStart() {
            super.onStart();

        }

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

            toastMessagges      = new ToastMessagges();

            AppStarter();
        }

        private void AppStarter(){

            boolean checkinternet   = InternetControl.checkInternetConnection( getApplicationContext() );
            if( checkinternet ) {
                toastMessagges.show_toast_messagge();
            }
            else {

            }

        }

        @Override
        public void LongToastMessagge() {
            Toast.makeText(getApplicationContext(), "Hello World", Toast.LENGTH_LONG).show();


}
}

这是我的 ToastMessagges.java 文件。

public class ToastMessagges {

    ToastMessaggeCallback toastMessaggeCallback;
    public void show_toast_messagge(){
        toastMessaggeCallback.LongToastMessagge();
    }


    public static interface ToastMessaggeCallback {
        public void LongToastMessagge();
    }
}

当启动这个应用程序时。我收到 NullPointerException 错误。

Caused by: java.lang.NullPointerException
            at com.medyasef.bulenttirasnewapp.bulenttiras.functions.ToastMessagges.show_toast_messagge(ToastMessagges.java:22)
            at com.medyasef.bulenttirasnewapp.bulenttiras.MotherActivity.AppStarter(MotherActivity.java:36)
            at com.medyasef.bulenttirasnewapp.bulenttiras.MotherActivity.onCreate(MotherActivity.java:29)

ToastMessagges.java:22

toastMessaggeCallback.LongToastMessagge();

抱歉英语不好。请帮忙。谢谢。

Answer 1

您尚未初始化ToastMessaggeCallback toastMessaggeCallback。

为此，请编写

ToastMessaggeCallback toastMessaggeCallback = new ToastMessaggeCallback(){

    public void LongToastMessagge(){
        // add some toasting code here
    }

};

这将创建一个实现您的接口(interface)的对象(称为“匿名类”)。当然，您的 ToastMessaggeCallback 应该在方法 LongToastMessagge 中执行某些操作，因此请在其中添加所需的代码。