Android：将项目添加到自定义列表视图

Question

I'm new to android programming and having trouble with adding items to listview with custom adapter. My program consist of list, textfield, spinner and button. The goal is to add new item to the list (with textfield's content as a name and spinner selection as a type), when the button is pressed. The problem is that items won't show up in the list. I have tried following several tutorials ( lastly this one ) but nothing seems to help. Here are my sources:

activity_list_view_demo.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >

<TextView
    android:id="@+id/textViewNum"
    android:text="0"
    android:layout_height="wrap_content"
    android:layout_width="fill_parent">
</TextView>
<Spinner
        android:id="@+id/shop"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:entries="@array/shop_name"
/>

 <ListView
    android:id="@+id/lista"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
/>

 <LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal" >

    <EditText
        android:id="@+id/txtItem"
        android:layout_gravity="bottom"
        android:layout_weight="4"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:inputType="text"
        android:hint="Esine"
    />

    <Spinner
        android:id="@+id/type"
        android:layout_gravity="bottom"
        android:layout_weight="2"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:entries="@array/type_name"
    />

    <Button
        android:id="@+id/btnAdd"
        android:layout_gravity="bottom"
        android:layout_weight="1"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:text="Lisää"
    />

</LinearLayout>

</LinearLayout>

listitem_row.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">

<TextView
    android:id="@+id/textViewName"
    android:text="TextView"
    android:layout_height="fill_parent"
    android:layout_width="fill_parent">
</TextView>

<TextView
    android:text="TextView"
    android:id="@+id/textViewType"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
</TextView>

</LinearLayout>

ListViewAdapter.java

package com.example.testi2;

import java.util.ArrayList;

import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class ListViewAdapter extends ArrayAdapter<ShoppingList>
{
Context context;
ArrayList<ShopItem> items;
int layoutResourceId = 0;

public ListViewAdapter(Context context, ShoppingList list, int resourceId) {
    super(context, R.layout.listitem_row);
    this.context = context;
    this.layoutResourceId = resourceId;

    for (int i = 0; i < list.getLength() - 1; i++) {
        items.add(list.getItem(i));
    }
}

@Override
public View getView(int position, View convertView, ViewGroup parent)
{
    View rowView = convertView;

    if (rowView == null) {
        LayoutInflater inflater = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        rowView = inflater.inflate(R.layout.listitem_row, null);
    }

    ShopItem i = items.get(position);

    if (i != null) {
        TextView nameView = (TextView) rowView.findViewById(R.id.textViewName);
        TextView typeView = (TextView) rowView.findViewById(R.id.textViewType);
        nameView.setText(i.getName());
        typeView.setText(i.getType());
    }

    return rowView;
}

}

ListViewDemo.java

package com.example.testi2;

import java.util.ArrayList;
import java.util.List;

import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.app.Activity;
import android.app.ListActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;
import android.os.Build;

public class ListViewDemo extends Activity {

private Spinner typeSpinner;    
private ListViewAdapter adapter;
private ListView lview;
private ShoppingList shoppinglist;

@Override
public void onCreate(Bundle icicle) {
    super.onCreate(icicle);
    setContentView(R.layout.activity_list_view_demo);

    shoppinglist = new ShoppingList();
    shoppinglist.addItem("Banaani", "Hedelmä");
    createAddBtn();
    createList();
    typeSpinner = (Spinner) findViewById(R.id.type);     
}

public void createList() {
    lview = (ListView) findViewById(R.id.lista);
    adapter=new ListViewAdapter(this, shoppinglist, R.layout.listitem_row);
    lview.setAdapter(adapter);
}

public void createAddBtn() {
    Button btn = (Button) findViewById(R.id.btnAdd);

    OnClickListener listener = new OnClickListener() {
        @Override
        public void onClick(View v) {
            EditText edit = (EditText) findViewById(R.id.txtItem);
            String editStr = edit.getText().toString();
            String spinnerStr = typeSpinner.getSelectedItem().toString();
            TextView numView = (TextView) findViewById(R.id.textViewNum);
            if (editStr.length()>0) {
                shoppinglist.addItem(editStr, spinnerStr);
                edit.setText("");
                adapter.notifyDataSetChanged();
                numView.setText(String.valueOf(shoppinglist.getItems().length));
            }
        }
    };       
    btn.setOnClickListener(listener);   
   }

   }

Any ideas what I'm doing wrong?

Answer 1

To start off, I would recommend you implement the ViewHolder pattern for any Adapter ( http://developer.android.com/training/improving-layouts/smooth-scrolling.html#ViewHolder ), but that is beyond the scope of this question.

To answer your question: you should look at where the Array adapter is getting its items. In your implementation's constructor, you are breaking any dependencies between the shopping list and the item array by simply copying over all the items. This results in any addition to the shopping list not transferring over to the adapters item list. Therefore, notifyDatasetChanged will have no effect.

To fix this problem, try using ArrayAdapters three parameter constructor that also takes an ArrayList so that you can keep a hard dependency between the adapter's dataset and the shopping list in the Activity.

Assuming ShoppingList simply extends ArrayList<ShopItem> , this would work like

public ListViewAdapter(Context context, ShoppingList list, int resourceId) {
    super(context, 0, list);
    this.context = context;
    this.layoutResourceId = resourceId;
}

Also, your ArrayAdapter should extend ArrayAdapter<ShopItem> , not ArrayAdapter<ShoppingList> . The generic should be the type of item to display, not the list.