我無法設置菜單項文本。我希望當我開始活動時看到籃子裏所有物品的價格。但每當我開始了購物清單的活動,我得到以下錯誤:設置菜單項文本
java.lang.NullPointerException: Attempt to invoke interface method 'android.view.MenuItem android.view.Menu.findItem(int)' on a null object reference
這是代碼:
public class Shopping_list_activity extends AppCompatActivity{
private Menu menu;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.shopping_list_activity);
updateMenuTitles();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
super.onCreateOptionsMenu(menu);
getMenuInflater().inflate(R.menu.menu_shopping_list, menu);
this.menu = menu;
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.menu_shopping_list_saveList) {
Toast.makeText(Shopping_list_activity.this, " Clicked", Toast.LENGTH_SHORT).show();
}
// else if (id == R.id.menu_shopping_list_total){
// Toast.makeText(Shopping_list_activity.this, getPriceOfDisplayedItems() + " total", Toast.LENGTH_SHORT).show();
// }
return super.onOptionsItemSelected(item);
}
private void updateMenuTitles() {
MenuItem menuItem = menu.findItem(R.id.menu_shopping_list_total);
if (getPriceOfDisplayedItems() > 0) {
menuItem.setTitle(String.valueOf(getPriceOfDisplayedItems()));
} else {
menuItem.setTitle("Total: 0.00");
}
}
的getPriceOfDisplayedItems()
顯示正確的價格。
和XML文件:
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools">
<item
android:id="@+id/menu_shopping_list_total"
android:title="@string/total"
app:showAsAction="always" />
</menu>
誰能幫我解決這個問題?
坦克很多,它工作正常,更新onCreateOptionsMenu中的總數。 – Adrian