在Firebase數據獲取方法中創建無限循環

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();
        }
    });
}

如果在失敗偵聽器中再次調用發生數據提取錯誤的方法，則它可以在啟動屏幕中運行，並且啟動是否繼續……是一種正確的方法

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

由於每次發生錯誤時， addOnFailureListener()觸發addOnFailureListener()方法，這就是調用fetchdata()方法，從而導致無限循環。 這種技術稱為recursion ，但在您的情況下根本無法幫助您。 要解決此問題，請僅處理Exception並使用以下代碼，而不是調用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
        }
    });
}