关于Java：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？

How to affect elements outside of a listview when some items in the listview are clicked?

我的content_main.xml布局中有一个ListView。该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。我需要能够这样做，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)来访问此文件。此方法在运行时返回null。

我尝试使用谷歌搜索，但是只能得到与我无关的不同主题的答案。

我是android的新手。解决这个问题的方法可能很简单，但是我找不到有关此问题的任何教程或有关stackoverflow的问题。

MainActivity.java

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93

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

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60

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

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30

`<?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

1
2
3
4
5
6
7
8
9
10
11
12
13
14

<?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

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

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;
}
}

相关讨论

您有三个选择(仅三个示例)：

使用ListView随附的单击侦听器。 (首选方法)
通过适配器构造函数注入依赖项。
使用侦听器模式来通知活动。

注意：我不确定为什么在调用getView方法时为什么需要更新TextView，可以经常调用getView退出(例如在滚动时)，这意味着TextView几乎会随机更新。我会选择选项1，这是对列表中项目的点击做出反应的最可靠，最可取的方式。

选项1：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

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：

1
2
3

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

选项3：

适配器：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67

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：

1
2
3
4
5
6
7
8
9
10

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

TextView text; //Init this in the onCreate

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