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Xamarin.Android ListView

  • Artikkeli

ListView is an important UI component of Android applications; it is used everywhere from short lists of menu options to long lists of contacts or internet favorites. It provides a simple way to present a scrolling list of rows that can either be formatted with a built-in style or customized extensively.

Overview

List views and adapters are included in the most fundamental building blocks of Android Applications. The ListView class provides a flexible way to present data, whether it is a short menu or a long scrolling list. It provides usability features like fast scrolling, indexes and single or multiple selection to help you build mobile-friendly user interfaces for your applications. A ListView instance requires an Adapter to feed it with data contained in row views.

This guide explains how to implement ListView and the various Adapter classes in Xamarin.Android. It also demonstrates how to customize the appearance of a ListView, and it discusses the importance of row re-use to reduce memory consumption. There is also some discussion of how the Activity Lifecycle affects ListView and Adapter use. If you are working on cross-platform applications with Xamarin.iOS, the ListView control is structurally similar to the iOS UITableView (and the Android Adapter is similar to the UITableViewSource).

First, a short tutorial introduces the ListView with a basic code example. Next, links to more advanced topics are provided to help you use ListView in real-world apps.

Note

The RecyclerView widget is a more advanced and flexible version of ListView. Because RecyclerView is designed to be the successor to ListView (and GridView), we recommend that you use RecyclerView rather than ListView for new app development. For more information, see RecyclerView.

ListView Tutorial

ListView is a ViewGroup that creates a list of scrollable items. The list items are automatically inserted to the list using a IListAdapter.

In this tutorial, you'll create a scrollable list of country/region names that are read from a string array. When a list item is selected, a toast message will display the position of the item in the list.

Start a new project named HelloListView.

Create an XML file named list_item.xml and save it inside the Resources/Layout/ folder. Insert the following:

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:padding="10dp"
    android:textSize="16sp">
</TextView>

This file defines the layout for each item that will be placed in the ListView.

Open MainActivity.cs and modify the class to extend ListActivity (instead of Activity):

public class MainActivity : ListActivity
{

Insert the following code for the OnCreate()) method:

protected override void OnCreate (Bundle bundle)
{
    base.OnCreate (bundle);

    ListAdapter = new ArrayAdapter<string> (this, Resource.Layout.list_item, countries);

    ListView.TextFilterEnabled = true;

    ListView.ItemClick += delegate (object sender, AdapterView.ItemClickEventArgs args)
    {
        Toast.MakeText(Application, ((TextView)args.View).Text, ToastLength.Short).Show();
    };
}

Notice that this does not load a layout file for the Activity (which you usually do with SetContentView(int))). Instead, setting the ListAdapter property automatically adds a ListView to fill the entire screen of the ListActivity. This method takes an ArrayAdapter<T>, which manages the array of list items that will be placed into the ListView. The ArrayAdapter<T> constructor takes the application Context, the layout description for each list item (created in the previous step), and a T[] or Java.Util.IList<T> array of objects to insert in the ListView (defined next).

The TextFilterEnabled property turns on text filtering for the ListView, so that when the user begins typing, the list will be filtered.

The ItemClick event can be used to subscribe handlers for clicks. When an item in the ListView is clicked, the handler is called and a Toast message is displayed, using the text from the clicked item.

You can use list item designs provided by the platform instead of defining your own layout file for the ListAdapter. For example, try using Android.Resource.Layout.SimpleListItem1 instead of Resource.Layout.list_item.

Add the following using statement:

using System;

Next, add the following string array as a member of MainActivity:

static readonly string[] countries = new String[] {
    "Afghanistan","Albania","Algeria","American Samoa","Andorra",
    "Angola","Anguilla","Antarctica","Antigua and Barbuda","Argentina",
    "Armenia","Aruba","Australia","Austria","Azerbaijan",
    "Bahrain","Bangladesh","Barbados","Belarus","Belgium",
    "Belize","Benin","Bermuda","Bhutan","Bolivia",
    "Bosnia and Herzegovina","Botswana","Bouvet Island","Brazil","British Indian Ocean Territory",
    "British Virgin Islands","Brunei","Bulgaria","Burkina Faso","Burundi",
    "Cote d'Ivoire","Cambodia","Cameroon","Canada","Cape Verde",
    "Cayman Islands","Central African Republic","Chad","Chile","China",
    "Christmas Island","Cocos (Keeling) Islands","Colombia","Comoros","Congo",
    "Cook Islands","Costa Rica","Croatia","Cuba","Cyprus","Czech Republic",
    "Democratic Republic of the Congo","Denmark","Djibouti","Dominica","Dominican Republic",
    "East Timor","Ecuador","Egypt","El Salvador","Equatorial Guinea","Eritrea",
    "Estonia","Ethiopia","Faeroe Islands","Falkland Islands","Fiji","Finland",
    "Former Yugoslav Republic of Macedonia","France","French Guiana","French Polynesia",
    "French Southern Territories","Gabon","Georgia","Germany","Ghana","Gibraltar",
    "Greece","Greenland","Grenada","Guadeloupe","Guam","Guatemala","Guinea","Guinea-Bissau",
    "Guyana","Haiti","Heard Island and McDonald Islands","Honduras","Hong Kong","Hungary",
    "Iceland","India","Indonesia","Iran","Iraq","Ireland","Israel","Italy","Jamaica",
    "Japan","Jordan","Kazakhstan","Kenya","Kiribati","Kuwait","Kyrgyzstan","Laos",
    "Latvia","Lebanon","Lesotho","Liberia","Libya","Liechtenstein","Lithuania","Luxembourg",
    "Macau","Madagascar","Malawi","Malaysia","Maldives","Mali","Malta","Marshall Islands",
    "Martinique","Mauritania","Mauritius","Mayotte","Mexico","Micronesia","Moldova",
    "Monaco","Mongolia","Montserrat","Morocco","Mozambique","Myanmar","Namibia",
    "Nauru","Nepal","Netherlands","Netherlands Antilles","New Caledonia","New Zealand",
    "Nicaragua","Niger","Nigeria","Niue","Norfolk Island","North Korea","Northern Marianas",
    "Norway","Oman","Pakistan","Palau","Panama","Papua New Guinea","Paraguay","Peru",
    "Philippines","Pitcairn Islands","Poland","Portugal","Puerto Rico","Qatar",
    "Reunion","Romania","Russia","Rwanda","Sqo Tome and Principe","Saint Helena",
    "Saint Kitts and Nevis","Saint Lucia","Saint Pierre and Miquelon",
    "Saint Vincent and the Grenadines","Samoa","San Marino","Saudi Arabia","Senegal",
    "Seychelles","Sierra Leone","Singapore","Slovakia","Slovenia","Solomon Islands",
    "Somalia","South Africa","South Georgia and the South Sandwich Islands","South Korea",
    "Spain","Sri Lanka","Sudan","Suriname","Svalbard and Jan Mayen","Swaziland","Sweden",
    "Switzerland","Syria","Taiwan","Tajikistan","Tanzania","Thailand","The Bahamas",
    "The Gambia","Togo","Tokelau","Tonga","Trinidad and Tobago","Tunisia","Turkey",
    "Turkmenistan","Turks and Caicos Islands","Tuvalu","Virgin Islands","Uganda",
    "Ukraine","United Arab Emirates","United Kingdom",
    "United States","United States Minor Outlying Islands","Uruguay","Uzbekistan",
    "Vanuatu","Vatican City","Venezuela","Vietnam","Wallis and Futuna","Western Sahara",
    "Yemen","Yugoslavia","Zambia","Zimbabwe"
  };

This is the array of strings that will be placed into the ListView.

Run the application. You can scroll the list, or type to filter it, then click an item to see a message. You should see something like this:

Example screenshot of ListView with country/region names

Note that using a hard-coded string array is not the best design practice. One is used in this tutorial for simplicity, to demonstrate the ListView widget. The better practice is to reference a string array defined by an external resource, such as with a string-array resource in your project Resources/Values/Strings.xml file. For example:

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <string name="app_name">HelloListView</string>
  <string-array name="countries_array">
    <item>Bahrain</item>
    <item>Bangladesh</item>
    <item>Barbados</item>
    <item>Belarus</item>
    <item>Belgium</item>
    <item>Belize</item>
    <item>Benin</item>
  </string-array>
</resources>

To use these resource strings for the ArrayAdapter, replace the original ListAdapter line with the following:

string[] countries = Resources.GetStringArray (Resource.Array.countries_array);
ListAdapter = new ArrayAdapter<string> (this, Resource.Layout.list_item, countries);

Run the application. You should see something like this:

Example screenshot of ListView with smaller list of names

Going Further with ListView

The remaining topics (linked below) take a comprehensive look at working with the ListView class and the different types of Adapter types you can use with it. The structure is as follows:

  • Visual Appearance – Parts of the ListView control and how they work.

  • Classes – Overview of the classes used to display a ListView.

  • Displaying Data in a ListView – How to display a simple list of data; how to implement ListView's usability features; how to use different built-in row layouts; and how Adapters save memory by re-using row views.

  • Custom appearance – Changing the style of the ListView with custom layouts, fonts and colors.

  • Using SQLite – How to display data from a SQLite database with a CursorAdapter.

  • Activity Lifecycle – Design considerations when implementing ListView Activities, including where in the lifecycle you should populate your data and when to release resources.

The discussion (broken into six parts) begins with an overview of the ListView class itself before introducing progressively more complex examples of how to use it.

Summary

This set of topics introduced ListView and provided some examples of how to use the built-in features of the ListActivity. It discussed custom implementations of ListView that allowed for colorful layouts and using an SQLite database, and it briefly touched on the relevance of the activity lifecycle on your ListView implementation.