Android開發教程：View Tag 的使用

發現Tag在View中還是很有作用的屬性，API中這樣描述的：

Tags

Unlike IDs, tags are not used to identify views. Tags are essentially an extra piece of information that can be associated with a view. They are most often used as a convenience to store data related to views in the views themselves rather than by putting them in a separate structure.

Tag不像ID是用標示view的。Tag從本質上來講是就是相關聯的view的額外的信息。它們經常用來存儲一些view的數據，這樣做非常方便而不用存入另外的單獨結構。

下面這個例子是從eoe中看到的，給我很大啟發：

1. public class FileListAdapter extends BaseAdapter {  
2.   
3.   
4.   
5.         private LayoutInflater mInflater;  
6.   
7.         private Bitmap mIcon_folder;  
8.   
9.         private Bitmap mIcon_file;  
10.   
11.         private Bitmap mIcon_image;  
12.   
13.         private Bitmap mIcon_audio;  
14.   
15.         private Bitmap mIcon_video;  
16.   
17.         private Bitmap mIcon_apk;  
18.   
19.         private List<String> items;  
20.   
21.         private List<String> paths;  
22.   
23.         private List<String> sizes;  
24.   
25.         private int isZoom = 0;  
26.   
27.   
28.   
29.         // MyAdapter的構造器   
30.   
31.         public FileListAdapter(Context context, List<String> it, List<String> pa,  
32.   
33.                         List<String> si, int zm) {  
34.   
35.                 mInflater = LayoutInflater.from(context);  
36.   
37.                 items = it;  
38.   
39.                 paths = pa;  
40.   
41.                 sizes = si;  
42.   
43.                 isZoom = zm;  
44.   
45.                 mIcon_folder = BitmapFactory.decodeResource(context.getResources(),  
46.   
47.                                 R.drawable.folder); // 文件夾的圖標   
48.   
49.                 mIcon_file = BitmapFactory.decodeResource(context.getResources(),  
50.   
51.                                 R.drawable.file); // 文件的圖文件   
52.   
53.                 mIcon_image = BitmapFactory.decodeResource(context.getResources(),  
54.   
55.                                 R.drawable.image); // 圖片的圖文件   
56.   
57.                 mIcon_audio = BitmapFactory.decodeResource(context.getResources(),  
58.   
59.                                 R.drawable.audio); // 音頻的圖文件   
60.   
61.                 mIcon_video = BitmapFactory.decodeResource(context.getResources(),  
62.   
63.                                 R.drawable.video); // 視頻的圖文件   
64.   
65.                 mIcon_apk = BitmapFactory.decodeResource(context.getResources(),  
66.   
67.                                 R.drawable.apk); // apk文件   
68.   
69.         }  
70.   
71.   
72.   
73.         @Override  
74.   
75.         public int getCount() {  
76.   
77.                 return items.size();  
78.   
79.         }  
80.   
81.   
82.   
83.         @Override  
84.   
85.         public Object getItem(int position) {  
86.   
87.                 return items.get(position);  
88.   
89.         }  
90.   
91.   
92.   
93.         @Override  
94.   
95.         public long getItemId(int position) {  
96.   
97.                 return position;  
98.   
99.         }  
100.   
101.   
102.   
103.         @Override  
104.   
105.         public View getView(int position, View convertView, ViewGroup par) {  
106.   
107.                 Bitmap bitMap = null;  
108.   
109.                 ViewHolder holder = null;  
110.   
111.                 if (convertView == null) {  
112.   
113.                         // 使用自定義的list_items作為Layout   
114.   
115.                         convertView = mInflater.inflate(R.layout.file_list_items, null);  
116.   
117.                         // 初始化holder的text與icon   
118.   
119.                         holder = new ViewHolder();  
120.   
121.                         holder.f_title = ((TextView) convertView.findViewById(R.id.f_title));  
122.   
123.                         holder.f_text = ((TextView) convertView.findViewById(R.id.f_text));  
124.   
125.                         holder.f_icon = ((ImageView) convertView.findViewById(R.id.f_icon));  
126.   
127.                         convertView.setTag(holder);  
128.   
129.                 } else {  
130.   
131.                         holder = (ViewHolder) convertView.getTag();  
132.   
133.                 }  
134.   
135.                 File f = new File(paths.get(position).toString());  
136.   
137.                 // 設置文件或文件夾的文字與icon   
138.   
139.                 holder.f_title.setText(f.getName());  
140.   
141.                 String f_type = MyUtil.getMIMEType(f, false);  
142.   
143.                 if (f.isDirectory()) {  
144.   
145.                         holder.f_icon.setImageBitmap(mIcon_folder);  
146.   
147.                         holder.f_text.setText("");  
148.   
149.                 } else {  
150.   
151.                         holder.f_text.setText(sizes.get(position));  
152.   
153.                         if ("image".equals(f_type)) {  
154.   
155.                                 if (isZoom == 1) {  
156.   
157.                                         bitMap = MyUtil.fitSizePic(f);  
158.   
159.                                         if (bitMap != null) {  
160.   
161.                                                 holder.f_icon.setImageBitmap(bitMap);  
162.   
163.                                         } else {  
164.   
165.                                                 holder.f_icon.setImageBitmap(mIcon_image);  
166.   
167.                                         }  
168.   
169.                                 } else {  
170.   
171.                                         holder.f_icon.setImageBitmap(mIcon_image);  
172.   
173.                                 }  
174.   
175.                                 bitMap = null;  
176.   
177.                         } else if ("audio".equals(f_type)) {  
178.   
179.                                 holder.f_icon.setImageBitmap(mIcon_audio);  
180.   
181.                         } else if ("video".equals(f_type)) {  
182.   
183.                                 holder.f_icon.setImageBitmap(mIcon_video);  
184.   
185.                         } else if ("apk".equals(f_type)) {  
186.   
187.                                 holder.f_icon.setImageBitmap(mIcon_apk);  
188.   
189.                         } else {  
190.   
191.                                 holder.f_icon.setImageBitmap(mIcon_file);  
192.   
193.                         }  
194.   
195.                 }  
196.   
197.                 return convertView;  
198.   
199.         }  
200.   
201.   
202.   
203.         /** 
204.  
205.          * 不單獨寫get set可以提高效率 class ViewHolder 
206.  
207.          * */  
208.   
209.         private class ViewHolder {  
210.   
211.                 TextView f_title;  
212.   
213.                 TextView f_text;  
214.   
215.                 ImageView f_icon;  
216.   
217.         }  
218.   
219. }