如何从按钮单击列表视图行获取对象答案

【问题标题】：How to get object from Button click on listview row如何从按钮单击列表视图行获取对象
【发布时间】：2020-01-19 21:03:15
【问题描述】：

当我单击 ListView 上一行上的按钮时，我正在尝试存储/获取对象。

所以，这是我点击 ListView 行的代码

            //Listview
            ListView mainListView = FindViewById<ListView>(Resource.Id.lstViewMain);

            //Custom adapter (taking a list "allComponents")
            ComponentListViewAdapter adapter = new ComponentListViewAdapter(this, allComponents);
            mainListView.Adapter = adapter;

            //Listview item/row click
            mainListView.ItemClick += MainListView_ItemClick;

        //Function to show the component's notes
        private void MainListView_ItemClick(object sender, AdapterView.ItemClickEventArgs e)
        {
            //Get the component tapped
            var component = allComponents[(int)e.Id];

            //Display message that the component was tapped
            Toast.MakeText(this, component.Name.ToString() + " Tapped", ToastLength.Long).Show();

            // Declare the activity as intent
            var intent = new Intent(this, typeof(View_NotesActivity));

            //Transfer the component's notes to the notes screen for display
            intent.PutExtra("component_notes", component.Notes);

            //Start the activity of intent
            StartActivity(intent);
         }

虽然当我实现与点击 ListView 行上的按钮时相同的逻辑时

            //Edit button
            ImageButton btnEditComponent = FindViewById<ImageButton>(Resource.Id.imgBtnEditComponent);
            btnEditComponent.Click += BtnEditComponent_Click;

        private void BtnEditComponent_Click(object sender, EventArgs e)
        {
            //throw new NotImplementedException();
        }

我收到错误“System.NullReferenceException: 'Object reference not set to an instance of an object.'”

我设法在自定义 ListView 适配器类中实现了编辑按钮，但我不知道如何访问 MainListView_ItemClick 函数中的“AdapterView.ItemClickEventArgs e”，以便将对象/组件存储在变量中，再次像在MainListView_ItemClick函数中如下：

        //Function to show the component's notes
        private void MainListView_ItemClick(object sender, AdapterView.ItemClickEventArgs e)
        {
            //Get the component tapped
            var component = allComponents[(int)e.Id];

这是在自定义 ListView 适配器类中实现编辑按钮（ListView 上的按钮）的两次尝试，我不知道如何访问/存储给定行的编辑按钮所在的组件。

            //Edit component button
            editComponent = row.FindViewById<ImageButton>(Resource.Id.imgBtnEditComponent);
            editComponent.Click += EditComponent_Click;

尝试 1：

        private void EditComponent_Click(object sender, EventArgs e)
        {
            //Get the component tapped
            //This does not work like it does with the ListView row tap function.
            //var component = allComponents[(int)e.Id];

            Toast.MakeText(mContext, e.ToString() + " Edited", ToastLength.Long).Show();
            //Retuns "System.EventArgs Edited"

            //throw new NotImplementedException();
        }

尝试 2：

            //Set on click listener for the Edit component Button
            editComponent.SetOnClickListener(this);

        public void OnClick(View v)
        {
            switch (v.Id)
            {
                case Resource.Id.imgBtnEditComponent:

                 //How can I grab the component when the only argument is a View?

                 break;
         }

非常感谢

【问题讨论】：

标签： listview android-listview xamarin.android listviewitem

【解决方案1】：

在你的适配器的GetView() 方法中试试这个：

//Edit component button
editComponent = row.FindViewById<ImageButton>(Resource.Id.imgBtnEditComponent);
editComponent.Tag = position;
//Set on click listener for the Edit component Button
editComponent.SetOnClickListener(this);

那么（如果 allComponents 是您的数据源）

public void OnClick(View v)
    {
      int position = （int）v.Tag；
      var component = allComponents[position];
    }

【讨论】：