如果单击列表视图中的某些项目，如何影响列表视图之外的元素？

Question

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

我创建了自己的名为ArrayAdapterItem的自定义适配器，它扩展了ArrayAdapter。在这个适配器的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。我需要能够这样做，因为如果单击列表中的某个项目，我想用新信息更新此TextView。但是我无法通过parent.findViewbyId（R.id.main_activity_textView）获得访问权限。此方法在运行时返回null。

我尝试使用Google搜索，但只能获得与我无关的不同主题的答案。

我是android的新手。解决方案可能很简单，但我找不到任何关于stackoverflow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_width="match_parent"
            android:layout_height="match_parent"
            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_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Hello World!"
                android:layout_alignParentTop="true"/>

            <ListView
                android:id="@+id/options_list"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                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_width="fill_parent"
        android:layout_height="fill_parent"
        android:padding="10dp" >

        <TextView
            android:id="@+id/textViewItem"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            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;
    }
}

Answer 1

您有三个选项（仅三个示例）：

• 使用ListView提供的单击侦听器。 （首选方法）
• 通过适配器构造函数注入依赖项。
• 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，可以经常调用getView（例如滚动时），这意味着TextView几乎会随机更新。我会选择选项1，这是对列表中项目点击做出反应的最可靠和首选方式。

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;

        }
    }

的活动：

public class ExampleActivity extends Activity implements UpdateActivity {
    //etc.

    TextView text; //Init this in the onCreate

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

Answer 2

在Android中使用listview适配器时，几乎总是将它们作为类的内部类使用它们 - 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。如果你想要更新的textView已经没有了，那就应该是它。

Answer 3

您可以使用LocalBroadCastManager，您可以在任何地方随时随地与您的应用进行通信

您可以使用此方法查看如何使用LocalBraodcastManager。

how to use LocalBroadcastManager?

Answer 4

你需要的不是很难再想一想你到底想要什么，

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

您可以轻松地从列表中获取对象，如此

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。对不起评论，但这是另一种转动汽车的方式：）

Answer 5

你应该替换：

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