以编程方式设置列表视图项的背景颜色 [英] Programmatically set the background color of a list view item

问题描述

在我的应用程序中，我必须根据该列表视图项的字符串内容自动设置 ListView 项的背景颜色.

In my app, I have to automatically set the background color of a ListView item, based on the string content of that list view item.

目前，该应用正在使用以下代码:

Currently, the app is using the below code:

    private void UpdateListView(string itemFromList, ListView listView)
    {
        int itemListPosition = listViewAdapter.GetPosition(itemFromList);
        listView.SetItemChecked(itemListPosition, true);

        View child = listView.GetChildAt(itemListPosition);

        if (child != null)
        {
            for (int i = 0; i < listViewAdapter.Count; i++)
            {
                View otherChild = listView.GetChildAt(i);

                if (otherChild != null)
                {
                    otherChild.SetBackgroundColor(defaultColor);
                }
            }

            child.SetBackgroundColor(Color.Green);
        }
    }

其中 listViewAdapter 是 MainActivity 类中的一个全局变量，如下定义到 onCreate 方法中:

where listViewAdapter is a global variable in the MainActivity class defined as below into the onCreate method:

listViewAdapter= new ArrayAdapter<String>(this, Android.Resource.Layout.SimpleListItem1, settingItems);
listView.Adapter = listViewAdapter;

和 settingItems 只是一个定义为字符串列表的全局变量.

and settingItems is just a global variable defined as a list of strings.

上述代码运行良好，因此给定列表视图项的背景颜色变为绿色，其余列表视图项变为默认颜色，直到列表视图向其添加垂直滚动.

The above code was working fine, so the background color of a given list view item was changing to green and the rest of the list view items to the default color, until the list view added a vertical scroll to it.

现在在列表视图获得更多项目和垂直滚动之后

Now after the list view got more items and a vertical scroll all the time the

View child = listView.GetChildAt(itemListPosition);

来自上述调用的

child 对象为空.因此，我无法再根据它们的位置访问列表视图中的项目.你知道我该如何解决这个问题吗?

child object from the above call is null. Consequently, I can't access anymore the items from the list view based on their position. Do you know how can I work around this?

推荐答案

我在GetView方法中写了一个demo，设置item的背景色，可以参考.

I wrote a demo in GetView method, set the item background color, you could refer to it.

这是演示的 GIF.

您可以在列表视图适配器的 GetView 方法中更改代码.我不知道你想在listview中更改哪些项目，所以我将位置设置在1、3、5.你可以自己改.

You could change code in the GetView method of listview adapter. I do not know which items you want to change in listview, so I set the position in 1,3,5. you could change it by yourself.

MyAdapter.cs

   class MyAdapter : BaseAdapter<ColorDemo>
{
    Activity context;
    List<ColorDemo> colors { get; set; }
    public MyAdapter(Activity context , List<ColorDemo> colors)
    {
        this.context = context;
        this.colors = colors;

    }

    public override ColorDemo this[int position] {
        get
        {
            return colors[position];
        }
    }

    public override int Count => colors.Count;



    public override long GetItemId(int position)
    {
        return position;
    }

    public override View GetView(int position, View convertView, ViewGroup parent)
    {
        View newView = convertView;
        if (newView == null)
            newView = context.LayoutInflater.Inflate(Resource.Layout.ItemView, null);
        newView.FindViewById<TextView>(Resource.Id.item_tv).Text = colors[position].ColorName;
        if (position==1|| position == 3|| position == 5)
        {
            newView.FindViewById<TextView>(Resource.Id.item_tv).SetBackgroundColor( Color.Blue);

        }
        else
        {
            newView.FindViewById<TextView>(Resource.Id.item_tv).SetBackgroundColor(Color.Green);

        }

       return newView;

    }
}

下面是activity_main.axml和ItemView.axml，你可以通过ItemView自定义listview中的item

The following is activity_main.axml and ItemView.axml, you could customize items in the listview by ItemView

activity_main.axml

 <?xml version="1.0" encoding="utf-8"?>
 <RelativeLayout 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"
     android:layout_width="match_parent"
     android:layout_height="match_parent">

    <ListView
        android:layout_width="match_parent"
        android:layout_height="match_parent" 
        android:id="@+id/lv_color"
     />
  </RelativeLayout>

ItemView.axml

<?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:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="this text"
    android:textSize="50dp"
    android:id="@+id/item_tv"
    android:background="@android:color/holo_red_dark"
    />
</LinearLayout>

以下代码与MainActivity.cs相关

The following code is related to the MainActivity.cs

MainActivity.cs

    [Activity(Label = "@string/app_name", Theme = "@style/AppTheme", MainLauncher = true)]
public class MainActivity : AppCompatActivity
{
    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        // Set our view from the "main" layout resource
        SetContentView(Resource.Layout.activity_main);
        ListView lv_color = FindViewById<ListView>(Resource.Id.lv_color);
       // lv_color.SetItemChecked(2,true);
        List<ColorDemo> colors = new List<ColorDemo>();
        colors.Add(new ColorDemo("red"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("red"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("red"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("red"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("red"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("red"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("green"));
        colors.Add(new ColorDemo("green"));

        MyAdapter myAdapter = new MyAdapter(this,colors);
        lv_color.Adapter=myAdapter;
    }
}

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