单击列表视图中的某些项目时如何影响列表视图之外的元素？

Posted 2023-05-07

【中文标题】单击列表视图中的某些项目时如何影响列表视图之外的元素？

【英文标题】：How to affect elements outside of a listview when some items in the listview are clicked?

【发布时间】：2016-03-30 18:26:11

【问题描述】：

我的 content_main.xml 布局中有一个 ListView。此列表视图的内容是通过 listview.setAdapter(myCustomAdapter) 设置的。我在 content_main.xml 布局中也有一个 TextView。

我创建了自己的自定义适配器，称为 ArrayAdapterItem，它扩展了 ArrayAdapter。在此适配器的 getView() 方法中，我试图访问 content_main.xml 中包含的 TextView。我不知道该怎么做。我需要能够做到这一点，因为如果单击列表中的某些项目，我想用新信息更新此 TextView。但是我无法通过 parent.findViewbyId(R.id.main_activity_textView) 访问它。此方法在运行时返回 null。

我尝试在谷歌上搜索，但只能获得与我无关的不同主题的答案。

我是安卓新手。解决这个问题的方法可能很简单，但我在 *** 上找不到任何与此相关的教程或问题。

MainActivity.java

package com.example.simran.listviewtest;

    import android.app.AlertDialog;
    import android.os.Bundle;
    import android.support.design.widget.FloatingActionButton;
    import android.support.design.widget.Snackbar;
    import android.support.v7.app.AppCompatActivity;
    import android.support.v7.widget.Toolbar;
    import android.view.View;
    import android.view.Menu;
    import android.view.MenuItem;
    import android.widget.ListView;

    public class MainActivity extends AppCompatActivity 
        AlertDialog alertDialogStores;
        @Override
        protected void onCreate(Bundle savedInstanceState) 
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
            setSupportActionBar(toolbar);

            showList();

            FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
            fab.setOnClickListener(new View.OnClickListener() 
                @Override
                public void onClick(View view) 
                    Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                            .setAction("Action", null).show();
                
            );
        

        public void showList()

            // add your items, this can be done programatically
            // your items can be from a database
            ObjectItem[] ObjectItemData = new ObjectItem[20];

            ObjectItemData[0] = new ObjectItem(91, "Mercury");
            ObjectItemData[1] = new ObjectItem(92, "Watson");
            ObjectItemData[2] = new ObjectItem(93, "Nissan");
            ObjectItemData[3] = new ObjectItem(94, "Puregold");
            ObjectItemData[4] = new ObjectItem(95, "SM");
            ObjectItemData[5] = new ObjectItem(96, "7 Eleven");
            ObjectItemData[6] = new ObjectItem(97, "Ministop");
            ObjectItemData[7] = new ObjectItem(98, "Fat Chicken");
            ObjectItemData[8] = new ObjectItem(99, "Master Siomai");
            ObjectItemData[9] = new ObjectItem(100, "Mang Inasal");
            ObjectItemData[10] = new ObjectItem(101, "Mercury 2");
            ObjectItemData[11] = new ObjectItem(102, "Watson 2");
            ObjectItemData[12] = new ObjectItem(103, "Nissan 2");
            ObjectItemData[13] = new ObjectItem(104, "Puregold 2");
            ObjectItemData[14] = new ObjectItem(105, "SM 2");
            ObjectItemData[15] = new ObjectItem(106, "7 Eleven 2");
            ObjectItemData[16] = new ObjectItem(107, "Ministop 2");
            ObjectItemData[17] = new ObjectItem(108, "Fat Chicken 2");
            ObjectItemData[18] = new ObjectItem(109, "Master Siomai 2");
            ObjectItemData[19] = new ObjectItem(110, "Mang Inasal 2");

            // our adapter instance
            ArrayAdapterItem adapter = new ArrayAdapterItem(this, R.layout.list_view_row_item, ObjectItemData);

            // create a new ListView, set the adapter and item click listener
            ListView listViewItems = (ListView)findViewById(R.id.main_activity_listView);
            listViewItems.setAdapter(adapter);
            listViewItems.setOnItemClickListener(new OnItemClickListenerListViewItem());

        

        @Override
        public boolean onCreateOptionsMenu(Menu menu) 
            // Inflate the menu; this adds items to the action bar if it is present.
            getMenuInflater().inflate(R.menu.menu_main, menu);
            return true;
        

        @Override
        public boolean onOptionsItemSelected(MenuItem item) 
            // Handle action bar item clicks here. The action bar will
            // automatically handle clicks on the Home/Up button, so long
            // as you specify a parent activity in AndroidManifest.xml.
            int id = item.getItemId();

            //noinspection SimplifiableIfStatement
            if (id == R.id.action_settings) 
                return true;
            

            return super.onOptionsItemSelected(item);
        
    

ArrayAdapterItem.java

            package com.example.simran.listviewtest;

        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.TextView;

        import org.w3c.dom.Text;

        /**
         * Created by simra on 12/23/2015.
         */
        public class ArrayAdapterItem extends ArrayAdapter<ObjectItem> 
            Context mContext;
            int layoutResourceId;
            ObjectItem data[] = null;

            public ArrayAdapterItem(Context mContext, int layoutResourceId, ObjectItem[] data) 
                super(mContext, layoutResourceId, data);

                this.layoutResourceId = layoutResourceId;
                this.mContext = mContext;
                this.data = data;
            


            @Override
            public View getView(int position, View convertView, ViewGroup parent) 

                /*
                 * The convertView argument is essentially a "ScrapView" as described is Lucas post
                 * http://lucasr.org/2012/04/05/performance-tips-for-androids-listview/
                 * It will have a non-null value when ListView is asking you recycle the row layout.
                 * So, when convertView is not null, you should simply update its contents instead of inflating a new row layout.
                 */
                if (convertView == null) 
                    // inflate the layout
                    LayoutInflater inflater = ((Activity) mContext).getLayoutInflater();
                    convertView = inflater.inflate(layoutResourceId, parent, false);
                

                //trying set the text of the textView in the main_activity.
                TextView mainActivityTextView = (TextView) parent.findViewById(R.id.main_activity_textView);
                mainActivityTextView.setText("some new text");

                // object item based on the position
                ObjectItem objectItem = data[position];

                // this sets the text and tag for the item in the list. Works fine
                TextView textViewItem = (TextView)   convertView.findViewById(R.id.textViewItem);
                textViewItem.setText(objectItem.itemName);
                textViewItem.setTag(objectItem.itemId);

                return convertView;

            
        

content_main.xml

     `<?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_
            android:layout_
            android:paddingBottom="@dimen/activity_vertical_margin"
            android:paddingLeft="@dimen/activity_horizontal_margin"
            android:paddingRight="@dimen/activity_horizontal_margin"
            android:paddingTop="@dimen/activity_vertical_margin"
            app:layout_behavior="@string/appbar_scrolling_view_behavior"
            tools:context="com.example.simran.listviewtest.MainActivity"
            tools:showIn="@layout/activity_main">

            <TextView
                android:id="@+id/hello_world"
                android:layout_
                android:layout_
                android:text="Hello World!"
                android:layout_alignParentTop="true"/>

            <ListView
                android:id="@+id/options_list"
                android:layout_
                android:layout_
                android:layout_below="@id/hello_world">

            </ListView>

        </RelativeLayout>`

list_view_row_item.xml

        <?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_
        android:layout_
        android:padding="10dp" >

        <TextView
            android:id="@+id/textViewItem"
            android:layout_
            android:layout_
            android:layout_alignParentTop="true"
            android:text="Item name here..."
            android:textSize="15dp" />
    </RelativeLayout>

ObjectItem.java

    package com.example.simran.listviewtest;

/**
 * Created by simra on 12/23/2015.
 */
public class ObjectItem 
    public int itemId;
    public String itemName;

    // constructor
    public ObjectItem(int itemId, String itemName) 
        this.itemId = itemId;
        this.itemName = itemName;
    

【问题讨论】：

你应该为适配器实现一个监听器，当在 listView 中单击某些项目时，它将更改 textView

@PankajNimgade 我不知道你的意思是什么？您是否想说在适配器的 getView() 方法中为每个单独的项目添加一个侦听器？你能详细说明你在说什么或者它在代码中的样子吗？或者您是说将侦听器添加到 mainActivity 类中的适配器？我是 Android 新手，所以我不明白你的意思。

@simcity，很抱歉有歧义，您只需添加一行代码即可完成您的要求，您将完成，我已经回答了，请检查它

【参考方案1】：

您有三个选项（仅三个示例）：

使用 ListView 提供的点击监听器。

（首选方法）

通过适配器构造函数注入依赖。 使用侦听器模式通知活动。

注意：我不确定为什么在调用 getView 方法时需要更新 TextView，getView 可以经常被调用退出（例如滚动时），这意味着 TextView 将几乎随机更新。我会选择选项 1，这是对列表中项目的点击做出反应的最可靠和首选的方式。

选项 1：

public class ExampleActivity extends Activity implements OnItemClickListener 

    private TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        //Set layout etc

        textView = (TextView) findViewById(some id); //Find the TextView

        ListView list = (ListView) findViewById(some id); //Find the ListView
        //Set adapter etc.
        list.setOnItemClickListener(this);
    


    @Override
    public void onItemClick(AdapterView<?> adapterView, View view, int pos, long id) 
        textView.setText("Some text"); //Get the text from your adapter for example
    

选项 2：

public ArrayAdapterItem(Context mContext, int layoutResourceId, ObjectItem[] data, TextView textview) 
    //etc.

选项 3：

适配器：

    package com.example.simran.listviewtest;

    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.TextView;

    import org.w3c.dom.Text;

    /**
     * Created by simra on 12/23/2015.
     */
    public class ArrayAdapterItem extends ArrayAdapter<ObjectItem> 
        Context mContext;
        int layoutResourceId;
        ObjectItem data[] = null;
        ArrayAdapterItemCallback callback;

        public interface ArrayAdapterItemCallback 
            updateText(String text);
        



        public ArrayAdapterItem(Context mContext, int layoutResourceId, ObjectItem[] data, ArrayAdapterItemCallback callback) 
            super(mContext, layoutResourceId, data);

            this.layoutResourceId = layoutResourceId;
            this.mContext = mContext;
            this.data = data;
            this.callback = callback;
        


        @Override
        public View getView(int position, View convertView, ViewGroup parent) 

            /*
             * The convertView argument is essentially a "ScrapView" as described is Lucas post
             * http://lucasr.org/2012/04/05/performance-tips-for-androids-listview/
             * It will have a non-null value when ListView is asking you recycle the row layout.
             * So, when convertView is not null, you should simply update its contents instead of inflating a new row layout.
             */
            if (convertView == null) 
                // inflate the layout
                LayoutInflater inflater = ((Activity) mContext).getLayoutInflater();
                convertView = inflater.inflate(layoutResourceId, parent, false);
            

            //trying set the text of the textView in the main_activity.
            callback.updateText("some new text");

            // object item based on the position
            ObjectItem objectItem = data[position];

            // this sets the text and tag for the item in the list. Works fine
            TextView textViewItem = (TextView)   convertView.findViewById(R.id.textViewItem);
            textViewItem.setText(objectItem.itemName);
            textViewItem.setTag(objectItem.itemId);

            return convertView;

        
    

活动：

public class ExampleActivity extends Activity implements UpdateActivity 
    //etc.

    TextView text; //Init this in the onCreate

    @Override
    void updateText(String text)
         text.setText(text);
    

【讨论】：

感谢您的回答。我曾考虑过这一点，但我想也许Android中有一种我不知道的更简单的方法。再次感谢您的快速回复。

@simcity 我为你添加了一个额外的选项；）

【参考方案2】：

在 Android 中使用 listview 适配器时，它们应该几乎总是被放置为使用它们的类的内部类 - 在这种情况下，它是您的 MainActivity 类。当适配器是内部类时，它可以使用封闭类的所有属性。如果您要更新的 textView 不存在，那么它应该在那里。

【参考方案3】：

您可以使用 LocalBroadCastManager，这样您就可以在您的应用程序中从任何地方到任何地方进行通信

你可以通过this查看，如何使用LocalBraodcastManager。

how to use LocalBroadcastManager?

【参考方案4】：

你需要的不是很努力尝试重新思考你到底想要什么，

您拥有的是TextView 来填充实例ObjectItem 类型的实例变量中的信息，

您可以像这样轻松地从单击的列表中获取对象

listView.setOnItemClickListener(new AdapterView.OnItemClickListener() 
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) 
                ObjectItem singleItem = (ObjectItem) listView.getItemAtPosition(position);
                textView.setText(""+singleItem.itemName);
                //this is the textView which you should already get the reference in Main Activity

            

        );

当你评估你需要什么时，很容易减少代码，没有必要实现一些你可能不会用于任何其他工作的代码。很抱歉发表评论，但这是另一种让你的车掉头的方法:)

【参考方案5】：

你应该替换：

parent.findViewById(...) by convertView.findViewById(...)