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。
最佳答案
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。
关于java - 我的界面触发时得到 NullPointerException，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22226315/