Android App - Effective List Adapter

admin

Effective List Adaptor 是指在清單中的每一個單項包含文字及圖片


建立新程式, package 名為 sample.effectiveAdaptor, 在 EffectiveAdapterActivity.java 檔案加入

1. package sample.effectiveAdaptor;
   
2. 
   
3. import android.app.ListActivity;
   
4. import android.content.Context;
   
5. import android.os.Bundle;
   
6. import android.view.LayoutInflater;
   
7. import android.view.View;
   
8. import android.view.ViewGroup;
   
9. import android.widget.BaseAdapter;
   
10. import android.widget.TextView;
    
11. import android.widget.ImageView;
    
12. import android.graphics.BitmapFactory;
    
13. import android.graphics.Bitmap;
    
14. 
    
15. /**
    
16. * Demonstrates how to write an efficient list adapter. The adapter used in this example binds
    
17. * to an ImageView and to a TextView for each row in the list.
    
18. *
    
19. * To work efficiently the adapter implemented here uses two techniques:
    
20. * - It reuses the convertView passed to getView() to avoid inflating View when it is not necessary
    
21. * - It uses the ViewHolder pattern to avoid calling findViewById() when it is not necessary
    
22. *
    
23. * The ViewHolder pattern consists in storing a data structure in the tag of the view returned by
    
24. * getView(). This data structures contains references to the views we want to bind data to, thus
    
25. * avoiding calls to findViewById() every time getView() is invoked.
    
26. */
    
27. public class EffectiveAdapterActivity extends ListActivity {
    
28. 
    
29.     private static class EfficientAdapter extends BaseAdapter {
    
30.         private LayoutInflater mInflater;
    
31.         private Bitmap mIcon1;
    
32.         private Bitmap mIcon2;
    
33. 
    
34.         public EfficientAdapter(Context context) {
    
35.             // Cache the LayoutInflate to avoid asking for a new one each time.
    
36.             mInflater = LayoutInflater.from(context);
    
37. 
    
38.             // Icons bound to the rows.
    
39.             mIcon1 = BitmapFactory.decodeResource(context.getResources(), R.drawable.icon48x48_1);
    
40.             mIcon2 = BitmapFactory.decodeResource(context.getResources(), R.drawable.icon48x48_2);
    
41.         }
    
42. 
    
43.         /**
    
44.          * The number of items in the list is determined by the number of speeches
    
45.          * in our array.
    
46.          *
    
47.          * @see android.widget.ListAdapter#getCount()
    
48.          */
    
49.         public int getCount() {
    
50.             return DATA.length;
    
51.         }
    
52. 
    
53.         /**
    
54.          * Since the data comes from an array, just returning the index is
    
55.          * sufficent to get at the data. If we were using a more complex data
    
56.          * structure, we would return whatever object represents one row in the
    
57.          * list.
    
58.          *
    
59.          * @see android.widget.ListAdapter#getItem(int)
    
60.          */
    
61.         public Object getItem(int position) {
    
62.             return position;
    
63.         }
    
64. 
    
65.         /**
    
66.          * Use the array index as a unique id.
    
67.          *
    
68.          * @see android.widget.ListAdapter#getItemId(int)
    
69.          */
    
70.         public long getItemId(int position) {
    
71.             return position;
    
72.         }
    
73. 
    
74.         /**
    
75.          * Make a view to hold each row.
    
76.          *
    
77.          * @see android.widget.ListAdapter#getView(int, android.view.View,
    
78.          *      android.view.ViewGroup)
    
79.          */
    
80.         public View getView(int position, View convertView, ViewGroup parent) {
    
81.             // A ViewHolder keeps references to children views to avoid unnecessary calls
    
82.             // to findViewById() on each row.
    
83.             ViewHolder holder;
    
84. 
    
85.             // When convertView is not null, we can reuse it directly, there is no need
    
86.             // to reinflate it. We only inflate a new View when the convertView supplied
    
87.             // by ListView is null.
    
88.             if (convertView == null) {
    
89.                 convertView = mInflater.inflate(R.layout.list_item_icon_text, null);
    
90. 
    
91.                 // Creates a ViewHolder and store references to the two children views
    
92.                 // we want to bind data to.
    
93.                 holder = new ViewHolder();
    
94.                 holder.text = (TextView) convertView.findViewById(R.id.text);
    
95.                 holder.icon = (ImageView) convertView.findViewById(R.id.icon);
    
96. 
    
97.                 convertView.setTag(holder);
    
98.             } else {
    
99.                 // Get the ViewHolder back to get fast access to the TextView
    
100.                 // and the ImageView.
     
101.                 holder = (ViewHolder) convertView.getTag();
     
102.             }
     
103. 
     
104.             // Bind the data efficiently with the holder.
     
105.             holder.text.setText(DATA[position]);
     
106.             holder.icon.setImageBitmap((position & 1) == 1 ? mIcon1 : mIcon2);
     
107. 
     
108.             return convertView;
     
109.         }
     
110. 
     
111.         static class ViewHolder {
     
112.             TextView text;
     
113.             ImageView icon;
     
114.         }
     
115.     }
     
116. 
     
117.     @Override
     
118.     public void onCreate(Bundle savedInstanceState) {
     
119.         super.onCreate(savedInstanceState);
     
120.         setListAdapter(new EfficientAdapter(this));
     
121.     }
     
122. 
     
123.     private static final String[] DATA = new String[] {
     
124.        "明治 青提朱古力橡皮糖96克", "萬樂珠 薄荷味37.5克",
     
125.        "瑞士糖 黑加侖味條裝49克", "瑞士糖 草莓口味條裝49克",
     
126.        "益達 香橙薄荷味袋裝28克", "爽浪 無糖香口珠 橙薑味28克",
     
127.        "爽浪 無糖香口珠 檸蜜味28克", "爽浪 無糖香口珠 西柚薄味28克",
     
128.        "爽浪無糖香口珠 超涼薄荷味28克", "珍寶珠 迷你珍寶珠 5支裝 30克",
     
129.        "利口樂潤喉糖 檸檬香草50克", "利口樂潤喉糖 接骨木花香草50克",
     
130.        "利口樂潤喉糖 黑加侖子香草50克", "得力素 檸檬糖10pc"
     
131.      };
     
132. }

複製代碼

在 list_item_icon_text.xml 加入以下內容:

1. <?xml version="1.0" encoding="utf-8"?>
   
2. <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   
3.     android:orientation="horizontal"
   
4.     android:layout_width="match_parent"
   
5.     android:layout_height="match_parent">
   
6. 
   
7.     <ImageView android:id="@+id/icon"
   
8.         android:layout_width="48dip"
   
9.         android:layout_height="48dip" />
   
10. 
    
11.     <TextView android:id="@+id/text"
    
12.         android:layout_gravity="center_vertical"
    
13.         android:layout_width="0dip"
    
14.         android:layout_weight="1.0"
    
15.         android:layout_height="wrap_content" />
    
16. 
    
17. </LinearLayout>

複製代碼

再在 res 建立新資料夾drawable , 把自己創迼的 icon48x48_1.png 及 icon48x48_1.png 加入