**Android常用適配器分析** Android中適配器是連接后端數據和前端顯示的適配器接口，是數據和UI之間重要的紐帶。系統中常見的View有ListView、GridView都要用到Adapter.列表控件是擴展了android.widget.AdapterView的類，包括ListView、GridView、Spinner和Gallery。而AdapterView本身實際上擴展了android.widget.ViewGroup，這意味著ListView、GridView等都是容器控件，換句話說列表控件包含一組視圖，適配器的用途是Adapter管理數據，并為其提供子視圖。 下圖是我在網上找到的比較全的Android適配器結構圖：  這里面最常用的幾個布局是ArrayAdapter、SimpleAdapter、CursorAdapter以及BaseAdapter。其中BaseAdapter是一個抽象類，需要子類繼承并實現其中的接口才能使用，常用于用戶自定義顯示比較復雜的數據。 **1）ArrayAdapter<T>** ArrayAdapter數組適配器是Android中最簡單的適配器，專門用于顯示列表控件。常用構造方法如下： ??? public ArrayAdapter(Context context, int textViewResourceId, List<T> objects); ??? public ArrayAdapter(Context context, int textViewResourceId, T[] objects); Demo1: ~~~ public class MainActivity extends Activity { private ListView listView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // setContentView(R.layout.activity_main); String[] strings = {"1", "2", "3", "4", "5"}; ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item1, strings); listView = new ListView(this); listView.setAdapter(adapter); setContentView(listView); } } ~~~ 注意：這里資源上針對子布局資源ID的前綴為android,意味著系統不在本地/res目錄中查找，會在系統自己的目錄中查找。位于SDK文件的platforms/android-version/data/res/layout目錄下，我們找到simple_list_item1.xml，其實際內容如下： ~~~ <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@android:id/text1" android:layout_width="match_parent" android:layout_height="wrap_content" android:textAppearance="?android:attr/textAppearanceListItemSmall" android:gravity="center_vertical" android:paddingStart="?android:attr/listPreferredItemPaddingStart" android:paddingEnd="?android:attr/listPreferredItemPaddingEnd" android:minHeight="?android:attr/listPreferredItemHeightSmall" /> ~~~ 這里strings可以是一個字符串數組，也可以是一個List集合。如： ~~~ private List<String> getData() { List<String> data = new ArratList<String>(); data.add("one"); data.add("two"); data.add("three"); data.add("four"); data.add("three"); return data; } ~~~ 在代碼中我們的Activity可以直接繼承于ListActivity，ListActivity類繼承與Activity類，默認綁定了一個ListView界面組件，并提供一些與列表視圖、處理相關的操作。 Demo2: ??? ~~~ public class MainActivity extends ListActivity { private ListView listView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item1, getData()); setListAdapter(adapter); } private List<String> getData() { List<String> data = new ArrayList<String>(); data.add("one"); data.add("two"); data.add("three"); return data; } } ~~~ **2)SimpleAdapter** ??? simpleAdapter的擴展性最好，可以定義各種各樣的布局，添加ImageView、Button、CheckBox等。 Demo: ??? simple_list.xml ~~~ <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="wrap_content" android:orientation="horizontal" > <TextView android:id="@+id/textView" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_margin="20dp" android:textIsSelectable="true" > </TextView> <ImageView android:id="@+id/img" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_margin="20sp" > </ImageView> </LinearLayout> ~~~ ??? MainActivity.java ~~~ public class MainActivity extends ListActivity { @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onCreate(savedInstanceState); String [] strings = new String[] {"title", "img"}; int[] ids = new int[] {R.id.textView, R.id.img}; SimpleAdapter adapter = new SimpleAdapter(this, getData(), R.layout.simple_list, strings, ids); setListAdapter(adapter); } private List<Map<String, Object>> getData() { List<Map<String, Object>> list = new ArrayList<Map<String,Object>>(); Map<String, Object> map = new HashMap<String, Object>(); map.put("title", "Hello"); map.put("img", R.drawable.iag); list.add(map); map = new HashMap<String, Object>(); map.put("title", "world"); map.put("img", R.drawable.ic_launcher); list.add(map); return list; } } ~~~ **3)CursorAdapter** ?? 一般要以數據庫為數據源的時候才會使用SimpleCursorAdapter.這個適配器也需要在ListView中使用，通過游標向列表提供數據。 Demo: ~~~ @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onCreate(savedInstanceState); Cursor cursor = getContentResolver().query(People.CONTENT_URI, null, null, null, null); startManagingCursor(cursor); ListAdapter adapter = new SimpleCursorAdapter(this, R.layout.simple_list, cursor, new String[] {People.NAME}, new int[] {R.id.textView}); setListAdapter(adapter); } ~~~ **4)BaseAdapter** 一般用于顯示復雜的列表布局，由于BaseAdapter是一個抽象類，使用該類需要自己寫一個適配器繼承于該類，并重新一些方法。 如下Demo我們通過ApplicationInfoAdapter繼承于BaseAdapter，實現一個簡單的Launcher，通過PackageManager查詢系統中Intent.ACTION_MAIN和Intent.CATEGORY_LAUNCHER的Activity并將其通過ListView的形式顯示出來，然后點擊某一項進入相應的Activity。 首先我們定義一個描述應用程序的類AppInfo: ~~~ public class AppInfo { private String appLabel; // 應用程序標簽 private Drawable appIcon; // 應用程序 的圖像 private Intent intent; private String pkgName; // 應用程序所對應包名 private Context context; public AppInfo(Context context) { this.context = context; } public String getAppLabel() { return appLabel; } public void setAppLabel(String appName) { this.appLabel = appName; } public Drawable getAppIcon() { return appIcon; } public void setAppIcon(Drawable appIcon) { this.appIcon = appIcon; } public Intent getIntent() { return intent; } public void setIntent(Intent intent) { this.intent = intent; } public String getPkgName() { return pkgName; } public void setPkgName(String pkgName) { this.pkgName = pkgName; } } ~~~ ???然后我們定義一個ApplicationInfoAdapter 繼承于BaseAdapter,并重寫其getCount()，getItem()，getItemId()，getView()等函數。 ~~~ public class ApplicationInfoAdapter extends BaseAdapter { private static final String TAG = "ApplicationInfoAdapter"; private List<AppInfo> mListAppInfo = null; LayoutInflater infater = null; public ApplicationInfoAdapter(Context context, List<AppInfo> apps) { // TODO Auto-generated constructor stub infater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); mListAppInfo = apps; } @Override public int getCount() { // TODO Auto-generated method stub Log.i(TAG, "size="+mListAppInfo.size()); return mListAppInfo.size(); } @Override public Object getItem(int arg0) { // TODO Auto-generated method stub return mListAppInfo.get(arg0); } @Override public long getItemId(int arg0) { // TODO Auto-generated method stub return 0; } @Override public View getView(int position, View convertView, ViewGroup viewGroup) { // TODO Auto-generated method stub Log.i(TAG, "getView at" + position); View view = null; ViewHolder holder = null; if(convertView == null || convertView.getTag()==null) { view = infater.inflate(R.layout.app_list, null); holder = new ViewHolder(view); view.setTag(holder); } else { view = convertView; holder = (ViewHolder)convertView.getTag(); } AppInfo appInfo = (AppInfo)getItem(position); holder.appIcon.setImageDrawable(appInfo.getAppIcon()); holder.tvAppLabel.setText(appInfo.getAppLabel()); holder.tvPktName.setText(appInfo.getPkgName()); return view; } class ViewHolder { ImageView appIcon; TextView tvAppLabel; TextView tvPktName; public ViewHolder(View view) { this.appIcon = (ImageView)view.findViewById(R.id.imgApp); this.tvAppLabel = (TextView)view.findViewById(R.id.tvAppLabel); this.tvPktName = (TextView)view.findViewById(R.id.tvPkgName); } } } ~~~ ?? 這里我們通過LAYOUT_INFLATER_SERVICE布局管理器服務動態加載app_list.xml用來顯示每一個應用程序的信息 ~~~ <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="50dp" android:orientation="horizontal" > <ImageView android:id="@+id/imgApp" android:layout_width="wrap_content" android:layout_height="fill_parent"> </ImageView> <RelativeLayout android:layout_width="fill_parent" android:layout_height="40dp" android:layout_marginLeft="10dp"> <TextView android:id="@+id/tvLabel" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="AppLabel:"> </TextView> <TextView android:id="@+id/tvAppLabel" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginLeft="3dp" android:text="Label" android:layout_toRightOf="@id/tvLabel" android:textColor="#ffD700"> </TextView> <TextView android:id="@+id/tvName" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_below="@id/tvLabel" android:text="包名"> </TextView> <TextView android:id="@+id/tvPkgName" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_below="@id/tvAppLabel" android:layout_alignLeft="@id/tvAppLabel" android:textColor="#ffD700"> </TextView> </RelativeLayout>" </LinearLayout> ~~~ 然后我們在MainActivity中通過PackageManager查詢系統中所有的ACTION_MAIN和 CATEGORY_LAUNCHER的屬性的Activity，通過ApplicationInfoAdapter適配器顯示到ListView上。 ~~~ public class MainActivity extends Activity implements OnItemClickListener { private static final String LOG_TAG = "MainActivity"; private static final int MSG_SUCCESS = 0; private ListView listView = null; private List<AppInfo> mListAppInfos = null; Handler mHandler = null; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); listView = (ListView) this.findViewById(R.id.listView); mListAppInfos = new ArrayList<AppInfo>(); mHandler = new Handler() { public void handleMessage(android.os.Message msg) { switch (msg.what) { case MSG_SUCCESS: ApplicationInfoAdapter applicationInfoAdapter = new ApplicationInfoAdapter( MainActivity.this, mListAppInfos); listView.setAdapter(applicationInfoAdapter); listView.setOnItemClickListener(MainActivity.this); break; default: break; } }; }; new Thread(new Runnable() { @Override public void run() { // TODO Auto-generated method stub queryAppInfo(); // 查詢所有應用程序信息 mHandler.obtainMessage(MSG_SUCCESS).sendToTarget(); } }).start(); } public void queryAppInfo() { PackageManager pm = this.getPackageManager(); /* List<ApplicationInfo> listApplications = pm.getInstalledApplications(PackageManager.GET_UNINSTALLED_PACKAGES); Collections.sort(listApplications, new ApplicationInfo.DisplayNameCoamparator(pm)); for(ApplicationInfo app : listApplications) { if((app.flags & ApplicationInfo.FLAG_SYSTEM) > 0) { // 系統程序 } else if( (app.flags & ApplicationInfo.FLAG_SYSTEM) <= 0) { // 第三方程序 } else if((app.flags & ApplicationInfo.FLAG_UPDATED_SYSTEM_APP) != 0) { // 系統程序被用戶更新了 } else if((app.flags & ApplicationInfo.FLAG_EXTERNAL_STORAGE) != 0) { // 安裝在SD卡程序 } }*/ Intent mainIntent = new Intent(Intent.ACTION_MAIN, null); mainIntent.addCategory(Intent.CATEGORY_LAUNCHER); // 查詢獲得所有ResolveInfo對象 List<ResolveInfo> resolveInfos = pm.queryIntentActivities(mainIntent, PackageManager.MATCH_DEFAULT_ONLY); for(ResolveInfo reInfo : resolveInfos) { Log.e(LOG_TAG, "name:"+reInfo.activityInfo.name + "pkg:"+reInfo.activityInfo.packageName); } // 根據name排序 Collections.sort(resolveInfos, new ResolveInfo.DisplayNameComparator(pm)); for(ResolveInfo reInfo : resolveInfos) { Log.e(LOG_TAG, "name:"+reInfo.activityInfo.name + "pkg:"+reInfo.activityInfo.packageName); } if(mListAppInfos != null) { mListAppInfos.clear(); for(ResolveInfo reInfo : resolveInfos) { String activityName = reInfo.activityInfo.name; // 獲得應用程序啟動Activity的name String pkgName = reInfo.activityInfo.packageName; // 獲得應用程序的包名 String appLabel = (String)reInfo.loadLabel(pm); // 獲得應用程序的Label Drawable icon = reInfo.loadIcon(pm); // 獲得應用程序的圖標 // 為應用程序的啟動Activity準備Intent Intent launchIntent = new Intent(); launchIntent.setComponent(new ComponentName(pkgName, activityName)); // 創建一個 AppInfo 對象 AppInfo appInfo = new AppInfo(this); appInfo.setAppLabel(appLabel); appInfo.setAppIcon(icon); appInfo.setPkgName(pkgName); appInfo.setIntent(launchIntent); mListAppInfos.add(appInfo); Log.i(LOG_TAG, "ActivityName:"+activityName+ "pkgName:"+pkgName); } } } @Override public void onItemClick(AdapterView<?> adapter, View view, int arg2, long arg3) { // TODO Auto-generated method stub Intent intent = mListAppInfos.get(arg2).getIntent(); Log.d(LOG_TAG, "intent:"+intent.toString()); startActivity(intent); } } ~~~