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私はこのオブジェクトの配列のリストに新しいオブジェクトを追加する責任がある以下のアクティビティを持っていますが、実行するとクラッシュします。 は、それが長いため、以下のすべてのクラスとエラーメッセージの一部です。ArrayListでエラーが発生しました<cart> items.add（new_item）;
第1アクティビティ：これは第2アクティビティを呼び出して結果を開始するアクティビティです。 itemDetails.java：
public class itemDetails extends AppCompatActivity implements View.OnClickListener{
int request_Code = 1;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.item);
Bundle received = getIntent().getExtras();
int position= received.getInt("position");
long id=received.getLong("id");
/*int id=0;getIntent().getIntExtra("id",id);
int position=0;*/
// getIntent().getIntExtra("id",id);getIntent().getIntExtra("position", position);
Toast.makeText(this, "id= " + id + ". and posistion= "+ position, Toast.LENGTH_LONG).show();
Integer[] picsId = {
R.drawable.pic1,
R.drawable.pic2,
R.drawable.pic3,
R.drawable.pic4,
R.drawable.pic5,
R.drawable.pic6,
R.drawable.pic7
};
String[] picsNames={"Rose", "Red Dahlia","Tulip","Red rose","Aloe","Mother-in-Law's tonque","Snake"};
String[] picCategory= {"Flowers","Flowers","Flowers","Flowers","Indoor plants","Indoor plants","Indoor plants"};
double[] prices={5.5, 4, 3, 6, 35, 40, 42 };
ImageView imgview = (ImageView) findViewById(R.id.item_image);
imgview.setImageResource(picsId[position]);
TextView nametxt= (TextView) findViewById(R.id.nametxtview);
TextView categorytxt= (TextView) findViewById(R.id.categorytxtview);
TextView pricetxt= (TextView) findViewById(R.id.pricetxtview);
nametxt.setText(picsNames[position]);
categorytxt.setText("Category: " + picCategory[position]);
pricetxt.setText(String.valueOf(prices[position]));
Button cart_button= (Button)findViewById(R.id.Add2cartbutton);
cart_button.setOnClickListener(this);
}
@Override
public void onClick(View v) {
TextView name= (TextView) findViewById(R.id.nametxtview);
TextView pricetxt = (TextView) findViewById(R.id.pricetxtview);
// cast the retrieved price to double type:
double price = Double.parseDouble(pricetxt.getText().toString());
Intent data= new Intent(this, AddnewItemToCart.class);
data.putExtra("name",name.getText().toString()); // store the item name in the new intent
data.putExtra("price", price); //, this saves the whole sentence
startActivityForResult(data,request_Code);
}
@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if(requestCode == request_Code){
if(resultCode == RESULT_OK) {
Toast.makeText(this, data.getStringExtra("name") + "is successfully added to your cart", Toast.LENGTH_SHORT).show();
}
}
}
}
次に、私のアプリケーションがクラッシュするアクティビティを示します。 AddnewItemToCart.java： ところで、どのレイアウトにも割り当てられていません。
public class AddnewItemToCart extends AppCompatActivity{
ArrayList<cart> items;
cart_adapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Bundle receivedData= getIntent().getExtras();
String name= receivedData.getString("name");
double price=receivedData.getDouble("price");
cart new_item= new cart(name,price); // created new Task object.
// Toast.makeText(this, new_item.itemName + " and "+ new_item.price , Toast.LENGTH_LONG).show();
items.add(new_item);
adapter.notifyDataSetChanged();
Intent data= new Intent();
data.putExtra("name",name);
setResult(RESULT_OK,data);
//---closes the activity---
finish();
}
}
そして、これが検出されたエラーメッセージです：
FATAL EXCEPTION: main
Process: swe.trial, PID: 4054
java.lang.RuntimeException: Unable to start activity ComponentInfo{swe.trial/swe.trial.CartActivity}: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2646)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
at android.app.ActivityThread.-wrap12(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1460)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6077)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:344)
at android.widget.ListView.setAdapter(ListView.java:493)
at swe.trial.CartActivity.onCreate(CartActivity.java:36)
at android.app.Activity.performCreate(Activity.java:6664)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2599)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2707)
package swe.trial;
は、これが主な活動ですが、それはそれを& AddnewItemToCart.javaをマージすることが可能である??で
public class CartActivity extends AppCompatActivity implements View.OnClickListener {
ArrayList<cart> items;
cart_adapter adapter;
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.shoppingcart);
ListView cart_list= (ListView) findViewById(R.id.cart_list);
cart_list.setAdapter(new cart_adapter(this, items));
Button checkout = (Button) findViewById(R.id.checkout);
}
@Override
public void onClick(View v) {
Bundle receivedData= getIntent().getExtras();
String name= receivedData.getString("name");
double price=receivedData.getDouble("price");
cart new_item= new cart(name,price); // created new Task object.
// Toast.makeText(this, new_item.itemName + " and "+ new_item.price , Toast.LENGTH_LONG).show();
items.add(new_item);
adapter.notifyDataSetChanged();
Intent data= new Intent();
data.putExtra("name",name);
setResult(RESULT_OK,data);
//---closes the activity---
finish();
// Toast.makeText(CartActivity.this, "Payment is not supported, Try again Later!", Toast.LENGTH_LONG).show();
}
}
class cart_adapter extends ArrayAdapter<cart> {
private ArrayList<cart> cart_items;
private Context context;
public cart_adapter(Context context, ArrayList<cart> items) {
super(context, R.layout.shoppingcart , items);
this.context = context;
this.cart_items = items;
}
public cart getItem(int position) {
return cart_items.get(position);}
public View getView(int position, View convertView, ViewGroup parent) {
cart item = getItem(position);
if (convertView == null) {
LayoutInflater inflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = inflater.inflate(R.layout.shoppingcart, parent, false);
}
TextView name= (TextView) convertView.findViewById(R.id.c_itemName);
TextView price= (TextView) convertView.findViewById(R.id.c_itemPrice);
name.setText(item.itemName);
price.setText("price: "+ item.price);
return convertView;
}
public long getItemId(int position) {
return position;
}
}
のように見えますか？ –
'items.add（new_item）;を実行する前に' items = new ArrayList <>（）; ' –