您好我正在创建一个带有标签的应用，我正在使用一个名为Cart的活动类，如下所示
public class Cart extends AppCompatActivity {
FragmentManager mFragmentManager;
FragmentTransaction mFragmentTransaction;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_mycart);
mFragmentManager = getSupportFragmentManager();
mFragmentTransaction = mFragmentManager.beginTransaction();
mFragmentTransaction.replace(R.id.containerView1,new MyCartTab()).commit();
}
}
在此活动中，我想调用下面代码中显示的Two Fixed标签
public class MyCartTab extends Fragment {
public static TabLayout tabLayout;
public static ViewPager viewPager;
public static int int_items = 2 ;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View x = inflater.inflate(R.layout.mycartdata,null);
tabLayout = (TabLayout) x.findViewById(R.id.carttabs);
viewPager = (ViewPager) x.findViewById(R.id.cartviewpager);
viewPager.setAdapter(new MyAdapter(getChildFragmentManager()));
tabLayout.post(new Runnable() {
@Override
public void run() {
tabLayout.setupWithViewPager(viewPager);
}
});
return x;
}
class MyAdapter extends FragmentPagerAdapter {
public MyAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return new My_Menu_List();
case 1:
return new My_Extra_List();
}
return null;
}
@Override
public int getCount() {
return int_items;
}
@Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "MyCart";
case 1:
return "MyExtras";
}
return null;
}
}
}
这是一个Tab活动文件MyCart
public class My_Menu_List extends android.support.v4.app.ListFragment {
ArrayList<Product> cart_list = new ArrayList<Product>();
ArrayList<Extra> ecart_list = new ArrayList<Extra>();
SQLiteDatabase sqLite;
int count=0;
int totalCartItemCount =0;
int totalCartValue = 0;
View view;
final String[] qtyValues = {"1","2","3","4","5","6","7","8","9","10"};
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
view = inflater.inflate(R.layout.myextralist, container, false);
TextView itemText = (TextView) view.findViewById(R.id.item_text);
TextView itemCount = (TextView) view.findViewById(R.id.cart_item_count);
TextView totalAmount = (TextView) view.findViewById(R.id.total_cart_amount);
Button checkout_cart = (Button) view.findViewById(R.id.checkout_cart);
ListView lv2=(ListView) view.findViewById(R.id.my_cart_list);
TextView cartEmpty = (TextView) view.findViewById(R.id.mycart_empty);
checkout_cart.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View view)
{
startActivity(new Intent(getActivity(),Customer_Payment.class));
}
});
getCartData();
try{
totalCartItemCount = (cart_list.size()+ecart_list.size());
totalCartValue =0;
for (int temp1=0; temp1 < cart_list.size(); temp1++) {
for (int temp2 = 0; temp2 < ecart_list.size(); temp2++) {
totalCartValue = totalCartValue + Integer.parseInt(cart_list.get(temp1).getFinalValue()) + Integer.parseInt(ecart_list.get(temp2).getExtraCheckoutPrice());
}
}
}catch(NumberFormatException n){n.printStackTrace();}
if (totalCartItemCount == 0)
{
itemText.setVisibility(view.INVISIBLE);
itemCount.setVisibility(view.INVISIBLE);
totalAmount.setVisibility(view.INVISIBLE);
checkout_cart.setVisibility(view.INVISIBLE);
lv2.setVisibility(view.INVISIBLE);
cartEmpty.setVisibility(view.VISIBLE);
}
else
{
itemText.setVisibility(view.VISIBLE);
itemCount.setVisibility(view.VISIBLE);
totalAmount.setVisibility(view.VISIBLE);
checkout_cart.setVisibility(view.VISIBLE);
lv2.setVisibility(view.VISIBLE);
cartEmpty.setVisibility(view.INVISIBLE);
}
itemCount.setText("("+ totalCartItemCount + ")");
totalAmount.setText("("+ totalCartValue +")");
lv2.setAdapter(new custom_list_one(getActivity(),cart_list));
return view;
}
class custom_list_one extends BaseAdapter
{
private LayoutInflater layoutInflater;
ViewHolder holder;
private ArrayList<Product> cartList=new ArrayList<Product>();
int cartCounter;
Context context;
public custom_list_one(Context context, ArrayList<Product> cart_list) {
layoutInflater = LayoutInflater.from(context);
this.cartList=cart_list;
this.cartCounter= cartList.size();
this.context = context;
}
@Override
public int getCount() {
return cartCounter;
}
@Override
public Object getItem(int arg0) {
return cartList.get(arg0);
}
@Override
public long getItemId(int arg0) {
return arg0;
}
@Override
public View getView(final int position, View convertView, ViewGroup parent)
{
Product tempProduct = cart_list.get(position);
if (convertView == null)
{
convertView = layoutInflater.inflate(R.layout.listone_custom, null);
holder = new ViewHolder();
holder.name = (TextView) convertView.findViewById(R.id.menu_name);
holder.price = (TextView) convertView.findViewById(R.id.menu_price);
holder.qty = (Spinner) convertView.findViewById(R.id.spinner1);
holder.cancel = (ImageButton) convertView.findViewById(R.id.delete);
holder.qty_text =(TextView) convertView.findViewById(R.id.qty_text);
holder.final_value = (TextView) convertView.findViewById(R.id.menu_price);
convertView.setTag(holder);
}
else
{
holder = (ViewHolder) convertView.getTag();
}
holder.name.setText(tempProduct.getName());
holder.price.setText("Rs "+tempProduct.getPrice());
ArrayAdapter<String> aa=new ArrayAdapter<String>(context,R.layout.qty_spinner_item,qtyValues);
aa.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
holder.qty.setAdapter(aa);
holder.qty.setSelection(Integer.parseInt(tempProduct.getMenuQty())-1);
holder.final_value.setText("Rs "+Integer.parseInt(tempProduct.getPrice())*Integer.parseInt(tempProduct.getMenuQty()));
holder.cancel.setOnClickListener(new MyPersonalClickListener("button_delete",tempProduct,context));
holder.qty.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener(){
@Override
public void onItemSelected(AdapterView<?> parent, View view,int selectionIndex, long id)
{
if ((parent.getSelectedItemPosition()+1) != Integer.parseInt(cart_list.get(position).getMenuQty())) {
sqLite=context.openOrCreateDatabase("mahatiffin", context.MODE_PRIVATE, null);
sqLite.execSQL("UPDATE CART SET MENU_QTY ='"+ (parent.getSelectedItemPosition()+1)+"' WHERE NAME ='"+cart_list.get(position).getName()+"'");
sqLite.execSQL("UPDATE CART SET FINAL_VALUE='" + (parent.getSelectedItemPosition()+1) * Integer.parseInt(cart_list.get(position).getPrice()) +"' WHERE NAME ='"+cart_list.get(position).getName()+"'");
sqLite.close();
getCartData();
notifyDataSetChanged();
//refresh data outside the listview - Cart Total, Total Items, Shipping Cost etc
View parentView = (View) view.getParent().getParent().getParent().getParent();
TextView txtTotalItems = (TextView) parentView.findViewById(R.id.cart_item_count);
TextView txtTotalAmount = (TextView) parentView.findViewById(R.id.total_cart_amount);
try{
totalCartItemCount = (cart_list.size()+ecart_list.size());
totalCartValue =0;
for (int temp1=0; temp1 < cart_list.size(); temp1++) {
for (int temp2 = 0; temp2 < ecart_list.size(); temp2++) {
totalCartValue = totalCartValue + Integer.parseInt(cart_list.get(temp1).getFinalValue()) + Integer.parseInt(ecart_list.get(temp2).getExtraCheckoutPrice());
}
}
}catch(NumberFormatException n){n.printStackTrace();}
txtTotalItems.setText("("+ totalCartItemCount + ")");
txtTotalAmount.setText("("+ totalCartValue +")");
}
}
@Override
public void onNothingSelected(AdapterView<?> arg0)
{
}
});
// notifyDataSetChanged();
return convertView;
}
class ViewHolder
{
TextView name;
TextView price;
TextView qty_text;
ImageButton cancel;
Spinner qty;
TextView final_value;
}
}
public class MyPersonalClickListener implements View.OnClickListener
{
String button_name;
Context context;
Product name;
public MyPersonalClickListener(String button_name, Product name, Context context)
{
this.context=context;
this.name = name;
this.button_name = button_name;
}
@Override
public void onClick(View v)
{
if (button_name == "button_delete")
{
sqLite=context.openOrCreateDatabase("mahatiffin", context.MODE_PRIVATE, null);
sqLite.execSQL("DELETE FROM CART WHERE NAME ='"+ name.getName()+"'");
sqLite.close();
Toast.makeText(context,"Item "+name.getName()+" delete from Cart", Toast.LENGTH_SHORT).show();
getCartData();
View lView = (View) v.getParent().getParent();
((ListView) lView).setAdapter(new custom_list_one(context,cart_list));
TextView txtTotalAmount = (TextView) view.findViewById(R.id.total_cart_amount);
TextView txtTotalItems = (TextView) view.findViewById(R.id.cart_item_count);
TextView itemText = (TextView) view.findViewById(R.id.item_text);
Button checkout_cart = (Button) view.findViewById(R.id.checkout_cart);
ListView listview2=(ListView) view.findViewById(R.id.my_cart_list);
TextView cartEmpty = (TextView) view.findViewById(R.id.mycart_empty);
try{
totalCartItemCount = (cart_list.size()+ecart_list.size());
totalCartValue =0;
for (int temp1=0; temp1 < cart_list.size(); temp1++) {
for (int temp2 = 0; temp2 < ecart_list.size(); temp2++) {
totalCartValue = totalCartValue + Integer.parseInt(cart_list.get(temp1).getFinalValue()) + Integer.parseInt(ecart_list.get(temp2).getExtraCheckoutPrice());
}
}
}catch(NumberFormatException n){n.printStackTrace();}
txtTotalItems.setText("("+ totalCartItemCount + ")");
txtTotalAmount.setText("("+ totalCartValue +")");
if (totalCartItemCount == 0)
{
itemText.setVisibility(view.INVISIBLE);
txtTotalItems.setVisibility(view.INVISIBLE);
txtTotalAmount.setVisibility(view.INVISIBLE);
checkout_cart.setVisibility(view.INVISIBLE);
listview2.setVisibility(view.INVISIBLE);
cartEmpty.setVisibility(view.VISIBLE);
}
else
{
itemText.setVisibility(view.VISIBLE);
txtTotalItems.setVisibility(view.VISIBLE);
txtTotalAmount.setVisibility(view.VISIBLE);
checkout_cart.setVisibility(view.VISIBLE);
listview2.setVisibility(view.VISIBLE);
cartEmpty.setVisibility(view.INVISIBLE);
}
}
}
}
public void getCartData()
{
Product tempCartItem;
cart_list.clear();
sqLite=getActivity().openOrCreateDatabase("mahatiffin", getActivity().MODE_PRIVATE, null);
sqLite.execSQL("CREATE TABLE IF NOT EXISTS TB_MENU (ID INTEGER primary key autoincrement,NAME VARCHAR, DESCRIPTION VARCHAR, PRICE INTEGER)");
sqLite.execSQL("CREATE TABLE IF NOT EXISTS CART (ID INTEGER primary key autoincrement, NAME VARCHAR, DESCRIPTION VARCHAR, PRICE INTEGER, MENU_QTY INTEGER, FINAL_VALUE INTEGER)");
Cursor c=sqLite.rawQuery("SELECT * FROM CART",null);
count=0;
if(c.moveToFirst())
{
do{
tempCartItem = new Product();
tempCartItem.setName(c.getString(c.getColumnIndex("NAME")));
tempCartItem.setPrice(c.getString(c.getColumnIndex("PRICE")));
tempCartItem.setMenuQty(c.getString(c.getColumnIndex("MENU_QTY")));
tempCartItem.setFinalValue(c.getString(c.getColumnIndex("FINAL_VALUE")));
cart_list.add(tempCartItem);
count++;
}while(c.moveToNext());
}
sqLite.close();
}
}
我的代码是正确的，但当我点击进入购物车活动页面时，它会显示错误。这是我的logcat
06-09 20：18：46.260 30923-30923 / com.androidbelieve.MahaTiffin E / AndroidRuntime：致命异常：主要 显示java.lang.NullPointerException 在 com.androidbelieve.MahaTiffin.My_Menu_List.onCreateView（My_Menu_List.java:84） 在 android.support.v4.app.Fragment.performCreateView（Fragment.java:1974） 在 android.support.v4.app.FragmentManagerImpl.moveToState（FragmentManager.java:1067） 在 android.support.v4.app.FragmentManagerImpl.moveToState（FragmentManager.java:1252） 在 android.support.v4.app.BackStackRecord.run（BackStackRecord.java:742） 在 android.support.v4.app.FragmentManagerImpl.execPendingActions（FragmentManager.java:1617） 在 android.support.v4.app.FragmentManagerImpl.executePendingTransactions（FragmentManager.java:570） 在 android.support.v4.app.FragmentPagerAdapter.finishUpdate（FragmentPagerAdapter.java:141） 在android.support.v4.view.ViewPager.populate（ViewPager.java:1177） 在android.support.v4.view.ViewPager.populate（ViewPager.java:1025） 在android.support.v4.view.ViewPager.onMeasure（ViewPager.java:1545） 在android.view.View.measure（View.java:15172） 在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:4842） 在 android.widget.LinearLayout.measureChildBeforeLayout（LinearLayout.java:1390） 在android.widget.LinearLayout.measureVertical（LinearLayout.java:681） 在android.widget.LinearLayout.onMeasure（LinearLayout.java:574） 在android.view.View.measure（View.java:15172） 在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:4842） 在android.widget.FrameLayout.onMeasure（FrameLayout.java:310） 在android.view.View.measure（View.java:15172） 在 android.widget.RelativeLayout.measureChildHorizontal（RelativeLayout.java:617） 在android.widget.RelativeLayout.onMeasure（RelativeLayout.java:399） 在android.view.View.measure（View.java:15172） 在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:4842） 在android.widget.FrameLayout.onMeasure（FrameLayout.java:310） 在 android.support.v7.widget.ContentFrameLayout.onMeasure（ContentFrameLayout.java:135） 在android.view.View.measure（View.java:15172） 在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:4842） 在 android.widget.LinearLayout.measureChildBeforeLayout（LinearLayout.java:1390） 在android.widget.LinearLayout.measureVertical（LinearLayout.java:681） 在android.widget.LinearLayout.onMeasure（LinearLayout.java:574） 在android.view.View.measure（View.java:15172） 在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:4842） 在android.widget.FrameLayout.onMeasure（FrameLayout.java:310） 在android.view.View.measure（View.java:15172） 在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:4842） 在 android.widget.LinearLayout.measureChildBeforeLayout（LinearLayout.java:1390） 在android.widget.LinearLayout.measureVertical（LinearLayout.java:681） 在android.widget.LinearLayout.onMeasure（LinearLayout.java:574） 在android.view.View.measure（View.java:15172） 在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:4842） 在android.widget.FrameLayout.onMeasure（FrameLayout.java:310） 在 com.android.internal.policy.impl.PhoneWindow $ DecorView.onMeasure（PhoneWindow.java:2167） 在android.view.View.measure（View.java:15172） 在android.view.ViewRootImpl.performMeasure（ViewRootImpl.java:1850） 在android.view.ViewRootImpl.measureHierarchy（ViewRootImpl.java:1102） 在android.view.ViewRootImpl.performTraversals（ViewRootImpl.java:1275） 在android.view.ViewRootImpl.doTraversal（ViewRootImpl.java:1000） 在 android.view.ViewRootImpl $ TraversalRunnable.run（ViewRootImpl.java:4222） 在 android.view.Choreographer $ CallbackRecord.run（Choreographer.java:725） 在android.view.Choreographer.doCallbacks（Choreographer.java:555） 在android.view.Choreographer.doFrame（Choreographer.java:525） 在 android.view.Choreographer $ FrameDisplayEventReceiver.run（Choreographer.java:711） 在android.os.Handler.handleCallback（Handler.java:615） 在android.os.Handler.dispatchMessage（Handler.java:92） 在android.os.Looper.loop（Looper.java:137） 在android.app.ActivityThread.main（ActivityThread.java:4918） at java.lang.reflect.Method.invokeNative（Native Method） 在java.lang.reflect.Method.invoke（
我是android的新手，这是我的第一个应用程序，所以请帮助解决这个错误。谢谢你提前。任何人请帮助我，我不知道我能为此NullPointerException错误做些什么。
这是我的第一个标签的XML文件，我的第二个标签xml文件也是相同的，只有名称是diff ..
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_alignParentBottom="true"
xmlns:android="http://schemas.android.com/apk/res/android">
<ListView
android:id="@+id/my_cart_list"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_above="@+id/rr"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_weight="1"
android:divider="#0af"/>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:layout_width="match_parent"
android:layout_height="50dp"
android:id="@+id/rr"
android:background="#FA0"
android:layout_marginBottom="0dp">
<TextView
android:id="@+id/item_text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Items"
android:textColor="#000"
android:textSize="17sp"
android:layout_marginTop="15dp"
android:layout_marginLeft="20dp"/>
<TextView
android:id="@+id/cart_item_count"
android:layout_toRightOf="@+id/item_text"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="(2)"
android:textColor="#000"
android:textSize="17sp"
android:layout_marginTop="15dp"
android:layout_marginLeft="5dp"/>
<TextView
android:id="@+id/total_cart_amount"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textColor="#000"
android:textSize="20sp"
android:layout_alignTop="@+id/cart_item_count"
android:layout_centerHorizontal="true" />
<Button
android:id="@+id/checkout_cart"
android:layout_width="wrap_content"
android:layout_height="25dp"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true"
android:layout_marginRight="4dp"
android:layout_marginTop="4dp"
android:padding="3dp"
android:text="Checkout >>"
android:textSize="16dp" />
<TextView
android:id="@+id/mycart_empty"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="CART IS EMPTY"
android:gravity="center"
android:textColor="#000"
android:textSize="22sp"
android:layout_marginTop="12dp"/>
</RelativeLayout>
</RelativeLayout>