在Firebase数据获取方法中创建无限循环

Question

private void fetchdata() {
    db.get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
        @Override
        public void onSuccess(DocumentSnapshot documentSnapshot) {
            ArrayList<String> cities = (ArrayList) documentSnapshot.get("cities");
            i = new Intent(Splash.this, Select.class);
            i.putStringArrayListExtra("cities", cities);
            startActivity(i);
        }

    }).addOnFailureListener(new OnFailureListener() {
        @Override
        public void onFailure(@NonNull Exception e) {

           /*do when the cities list is not fetch  */
            fetchdata();
        }
    });
}

如果在失败侦听器中再次调用发生数据提取错误的方法，则它可以在启动屏幕中运行，并且启动是否继续……是一种正确的方法

Answer 1

private void fetchdata() {
    ArrayList<String> cities = new ArrayList<String>();
    i = new Intent(Splash.this, Select.class);

    db.get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
        @Override
        public void onSuccess(DocumentSnapshot documentSnapshot) {

            cities = (ArrayList) documentSnapshot.get("cities");
            i.putStringArrayListExtra("cities", cities);
            startActivity(i);
        }
    }).addOnFailureListener(new OnFailureListener() {
        @Override
        public void onFailure(@NonNull Exception e) {

            /* simple startActivity  */
            i.putStringArrayListExtra("cities", cities);
            startActivity(i);
        }
    });
}

Answer 2

由于每次发生错误时， addOnFailureListener()触发addOnFailureListener()方法，这就是调用fetchdata()方法，从而导致无限循环。 这种技术称为recursion ，但在您的情况下根本无法帮助您。 要解决此问题，请仅处理Exception并使用以下代码，而不是调用fetchdata()方法：

private void fetchdata() {
    db.get().addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() {
        @Override
        public void onSuccess(DocumentSnapshot documentSnapshot) {
            List<String> cities = (ArrayList) documentSnapshot.get("cities");
            Intent intent = new Intent(Splash.this, Select.class);
            intent.putStringArrayListExtra("cities", cities);
            startActivity(intent);
        }
    }).addOnFailureListener(new OnFailureListener() {
        @Override
        public void onFailure(@NonNull Exception e) {
            e.printStackTrace(); //Handle Exception
        }
    });
}