嘗試在 null object 引用上調用虛方法“void android.widget.TextView.setVisibility(int)”

Question

我在由 textview 組成的通知上將 textview 計數設置為VISIBLE ，但我收到錯誤 java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.8841843.set8008(8841843.set8008)一個 null object 參考

主要活動

reference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
            for (DataSnapshot childSnapshot: snapshot.getChildren()) {
                ids.add(childSnapshot.getKey());
            }


            int i;
            for ( i = 0 ; i < ids.size();i++)
            {
                ref = FirebaseDatabase.getInstance().getReference().child("Items").child(ids.get(i));

                ref.addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot snapshot) {

                        for (DataSnapshot childSnapshot: snapshot.getChildren()) {
                            hashmap.put(childSnapshot.getKey(),childSnapshot.getValue().toString());
                        }


                        if(Integer.parseInt(hashmap.get("qty"))<=25)
                        {
                            badge.setVisibility(View.VISIBLE);

                        }
                    }

                    @Override
                    public void onCancelled(@NonNull DatabaseError error) {

                    }
                });


            }

在創建選項菜單上

 @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater mi = getMenuInflater();
        mi.inflate(R.menu.actionbar,menu);
         View notificaitons = menu.findItem(R.id.notification).getActionView();
        ImageButton iconButtonMessages = (ImageButton) notificaitons.findViewById(R.id.badge_icon_button);
        badge = (TextView) notificaitons.findViewById(R.id.noti);
        iconButtonMessages.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent =new Intent(MainActivity.this,Notification.class);
                startActivity(intent);

            }
        });

        return super.onCreateOptionsMenu(menu);
    }

onOptionsItemSelected

@Override
public boolean onOptionsItemSelected(@NonNull MenuItem item) {
    switch (item.getItemId()) {
        case R.id.notification:
            Intent intentHome = new Intent(this, Notification.class);
            startActivity(intentHome);
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }
}

Answer 1

reference.addValueEventListener(...)

你什么時候運行這段代碼？

我假設您在初始化badge object 之前收到對 ValueEventListener 偵聽器的回調