使用ContentProvider访问非数据库数据

8270阅读　0评论2017-03-03　landuochong
分类：Android平台

一般情况我们使用ContentProvider主要访问数据库数据，但有时也可能需要访问非数据库数据，如XML或者本地数据，那就需要做一下特殊处理
最主要的是需要自定义Cursor，因为ContentProvider的query方法，只能返回Cursor引用。直接上代码，咱们边看边说

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  1. public class MyContentProvider extends ContentProvider {
  2.     
  3.     //操作URI的类
  4.     public static final UriMatcher uriMatcher;
  5.     //为UriMatcher添加自定义的URI
  6.     static{
  7.         uriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
  8.         uriMatcher.addURI(ProviderConstant.AUTHORITIES,"/user",
  9.                 ProviderConstant.INCOMING_USER_COLLECTION);
  10.         uriMatcher.addURI(ProviderConstant.AUTHORITIES,"/user/#",
  11.                 ProviderConstant.INCOMING_USER_SINGLE);
  12.     }

  14.     private HashMap<String,ArrayList<String>> allDatas= new HashMap<String,ArrayList<String>>();
  15.        
  16.     
  17.     private MyCursor cursor;
  18.     
  19.     public MyContentProvider(){
  20.         cursor = new MyCursor();
  21.         loadAllData();
  22.     }
  23.     
  24.     
  25.     /**
  26.      * 加载我们的数据信息
  27.      */
  28.     public void loadAllData(){
  29.         allDatas.clear();
  30.         for(int pos=0; pos < 5;pos++){//填充5个学生数据
  31.             ArrayList<String> dataList = new ArrayList<>();
  32.             dataList.add(pos+"");//id
  33.             dataList.add("name"+pos);//name
  34.             allDatas.put(pos+"",dataList);
  35.         }
  36.     }
  37.     
  38.     /**
  39.      * 删除数据
  40.      */
  41.     @Override
  42.     public int delete(Uri uri, String selection, String[] selectionArgs) {
  43.         System.out.println("delete");
  44.         int count = 0;
  45.         String id = getUserId(selection, selectionArgs);
  46.         if(allDatas.containsKey(id)){
  47.             allDatas.remove(id);
  48.             count = 1;
  49.         }
  50.         return count;
  51.     }

  53.     /**
  54.      * 数据库访问类型
  55.      */
  56.     @Override
  57.     public String getType(Uri uri) {
  58.         System.out.println("getType");
  59.         //根据用户请求，得到数据类型
  60.         switch (uriMatcher.match(uri)) {
  61.             case ProviderConstant.INCOMING_USER_COLLECTION:
  62.                 return ProviderConstant.CONTENT_TYPE;
  63.             case ProviderConstant.INCOMING_USER_SINGLE:
  64.                 return ProviderConstant.CONTENT_TYPE_ITEM;
  65.             default:
  66.                 throw new IllegalArgumentException("UnKnown URI"+uri);
  67.         }
  68.     }

  70.     /**
  71.      * 插入数据
  72.      */
  73.     @Override
  74.     public Uri insert(Uri uri, ContentValues values) {
  75.         ArrayList<String> data = new ArrayList<>();
  76.         int id =values.getAsInteger(ProviderConstant.ID);
  77.         String name = values.getAsString(ProviderConstant.NAME);
  78.         data.add(id+"");
  79.         data.add(name);
  80.         allDatas.put(id+"", data);
  81.         return uri;
  82.     }

  84.     /**
  85.      * 创建ContentProvider时调用的回调函数
  86.      */
  87.     @Override
  88.     public boolean onCreate() {
  89.         System.out.println("onCreate");
  90.         return true;
  91.     }

  93.     /**
  94.      * 查询数据库
  95.      */
  96.     @Override
  97.     public Cursor query(Uri uri, String[] projection, String selection,
  98.             String[] selectionArgs, String sortOrder) {
  99.         //判断用户请求，查询所有还是单个
  100.         switch(uriMatcher.match(uri)){
  101.             case ProviderConstant.INCOMING_USER_COLLECTION:
  102.                cursor.updateAllData(allDatas.values());
  103.                 break;
  104.             case ProviderConstant.INCOMING_USER_SINGLE:
  105.                 String id = uri.getLastPathSegment();
  106.                 cursor.updateUserData(allDatas.get(id));
  107.                 break;
  108.         }
  109.         return cursor;
  110.     }

  112.     /**
  113.      * 更新数据库
  114.      */
  115.     @Override
  116.     public int update(Uri uri, ContentValues values, String selection,
  117.             String[] selectionArgs) {
  118.         System.out.println("update");
  119.         String id = getUserId(selection, selectionArgs);
  120.         int count=0;
  121.         if(allDatas.containsKey(id)){
  122.             String name = values.getAsString(ProviderConstant.NAME);
  123.             //index取决于name所在的列
  124.             allDatas.get(id).set(cursor.getColumnIndex(ProviderConstant.NAME), name);
  125.             count = 1;
  126.         }
  127.         return count;
  128.     }
  129.     
  130.     /**
  131.      * 获取关键信息，用户ID
  132.      * @param selection
  133.      * @param selectionArgs
  134.      * @return
  135.      */
  136.     private String getUserId(String selection, String[] selectionArgs){
  137.         if(selectionArgs == null || selectionArgs.length == 0){
  138.             //id 包含在selection里
  139.             return selection.substring(selection.indexOf("=")+1).trim();
  140.         }else{
  141.             return selectionArgs[0];
  142.         }
  143.     }

  145. }
以上是自定义contentProvider，网上有很多例子和说明，不在详述，我们主要看一下query，我返回自定义Cursor。
其中用到了一些常量如下：

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  1. public class ProviderConstant {
  2.   //URI的指定，此处的字符串必须和声明的authorities一致
  3.    public static final String AUTHORITIES = "com.zy.sports.app.MyContentProvider";

  5.    //访问该ContentProvider的URI
  6.    public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITIES + "/user");
  7.    
  8.    //该ContentProvider所返回的数据类型的定义
  9.    public static final String CONTENT_TYPE = "vnd.android.cursor.dir/vnd.myprovider.user";
  10.    public static final String CONTENT_TYPE_ITEM = "vnd.android.cursor.item/vnd.myprovider.user";
  11.    
  12.    
  13.    //访问表的所有列
  14.    public static final int INCOMING_USER_COLLECTION = 1;
  15.    //访问单独的列
  16.    public static final int INCOMING_USER_SINGLE = 2;
  17.    
  18.    
  19.    public static final String ID = "id";
  20.    public static final String NAME = "name";

  22. }



自定义Cursor的代码如下：

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  1. public class MyCursor extends AbstractCursor{
  2.     private static final String TAG = "MyCursor";
  3.     
  4.     private String[] columnNames= null;//构建cursor时必须先传入列明数组以规定列数

  6.     /**
  7.      * 数据区域
  8.      */
  9.     //所有的数据
  10.     private ArrayList<ArrayList<String>> allDatas= new ArrayList<ArrayList<String>>();//在构造的时候填充数据，里层数据的size=columnNames.leng
  11.     //当前一项的数据
  12.     private ArrayList<String> oneLineData= null;//onMove时填充

  14.     public MyCursor(){
  15.         //必须构建完整列信息
  16.         columnNames = new String[]{"id","name"};
  17.     }
  18.     
  19.     /**
  20.      * 加载我们的数据信息
  21.      */
  22.     public void updateAllData(Collection<ArrayList<String>> data){
  23.         mPos = -1;
  24.         allDatas.clear();
  25.         allDatas.addAll(data);
  26.     }
  27.     
  28.     /**
  29.      * 加载我们的数据信息
  30.      */
  31.     public void updateUserData(ArrayList<String> data){
  32.         mPos = -1;
  33.         allDatas.clear();
  34.         allDatas.add(data);
  35.     }

  37.     /**
  38.      * 获取当前行对象，为一个oneLineDatastring[]
  39.      */

  41.     @Override
  42.     public boolean onMove(int oldPosition, int newPosition) {
  43.         if(newPosition< 0 || newPosition >= getCount()){
  44.             oneLineData= null;
  45.             return false;
  46.         }

  48.         int index = newPosition ;
  49.         if(index< 0 || index >= allDatas.size()){
  50.             return false;
  51.         }
  52.         oneLineData= allDatas.get(index);
  53.         return super.onMove(oldPosition,newPosition);
  54.     }

  56.     /**
  57.      *获取游标行数
  58.      */
  59.     @Override
  60.     public int getCount() {
  61.         return allDatas.size();
  62.     }

  64.     /**
  65.      * 获取列名称
  66.      */
  67.     @Override
  68.     public String[] getColumnNames() {
  69.         return columnNames;
  70.     }


  73.     @Override
  74.     public String getString(int column) {
  75.         if(oneLineData== null){
  76.             return null;
  77.         }
  78.         return oneLineData.get(column);
  79.     }
  80.     
  81.     @Override
  82.     public int getInt(int column) {
  83.         Object value = getString(column);
  84.         try{
  85.             return value != null? ((Number) value).intValue() : null;
  86.         } catch(ClassCastException e) {
  87.             if(value instanceof CharSequence) {
  88.                 try{
  89.                     return Integer.valueOf(value.toString());
  90.                 } catch(NumberFormatException e2) {
  91.                     Log.e(TAG,"Cannotparse int value for "+ value + "at key "+ column);
  92.                     return 0;
  93.                 }
  94.             } else{
  95.                 Log.e(TAG,"Cannotcast value for "+ column + "to a int: "+ value, e);
  96.                 return 0;
  97.             }
  98.         }
  99.     }

  101.     /**
  102.      * 以下参考getInt(int column)
  103.      */
  104.     
  105.     @Override
  106.     public short getShort(int column) {
  107.         return 0;
  108.     }

  110.     @Override
  111.     public long getLong(int column) {
  112.         return 0;
  113.     }

  115.     @Override
  116.     public float getFloat(int column) {
  117.         return 0;
  118.     }

  120.     @Override
  121.     public double getDouble(int column) {
  122.         return 0;
  123.     }

  125.     @Override
  126.     public boolean isNull(int column) {
  127.         return false;
  128.     }
  129. }
 我们看到Cursor是一个接口，我们只需要继承AbstractCursor或者他的子类来重定义Cursor的方法。大家可以参考，欢迎多提意见





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