为什么要引入ContentProvider

为什么要引入ContentProvider？
Android提供了文件存储数据，文件的存储格式不受限制，但是这样不方便数据的管理。为了方便管理，我们一般采用xml文件存储数据。对于这样的数据操作，我们必须对其进行xml文件解析。
所以Android的Sharepreferences(共享参数的方式)由此诞生。它是xml文件的方式存储数据，存储在包下shared_prefs目录中，它提供了API方便我们对xml文件操作。
但是文件和共享参数的方式虽然可以方便的存储数据，这样的文件要被其他应用访问，又要修该源代码，这样对我们造成了不便。
所以ContentProvider由此应运而生。ContentProvider只需向外提供域名，其他应用通过相应的API即可对其操作。

文件方式如下：

public class SharePreferencesActivity extends Activity {    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        final SharedPreferences sharedPreferences = getSharedPreferences("jefry", Context.MODE_APPEND);                Button save = (Button)findViewById(R.id.save);        save.setOnClickListener(new View.OnClickListener() {public void onClick(View arg0) {Log.i("SharePreferencesActivity", Thread.currentThread().getName());Editor editor = sharedPreferences.edit();EditText nameEd = (EditText) findViewById(R.id.filename);EditText content = (EditText) findViewById(R.id.content);    editor.putString("name",nameEd.getText().toString().trim());    editor.putInt("age", new Integer(content.getText().toString().trim()));    editor.commit();//提交修改       }  });    }}

Sharepreferences如下

public class SharePreferencesActivity extends Activity {    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        final SharedPreferences sharedPreferences =         getSharedPreferences("jefry", Context.MODE_APPEND);                Button save = (Button)findViewById(R.id.save);        save.setOnClickListener(new View.OnClickListener() {public void onClick(View arg0) {Log.i        ("SharePreferencesActivity", Thread.currentThread       ().getName());Editor editor =        sharedPreferences.edit();EditText nameEd = (EditText) findViewById(R.id.filename);EditText content = (EditText) findViewById(R.id.content);    editor.putString("name",nameEd.getText().toString().trim());    editor.putInt("age", new Integer(content.getText().toString().trim()));    editor.commit();//提交修改       }  });    }}

ContentProvider方式如下：

public class PersonContentProvider extends ContentProvider {private static final UriMatcher sMatcher = new UriMatcher(UriMatcher.NO_MATCH);static {sMatcher.addURI("com.contentprovider.personprovider", "person", 1);sMatcher.addURI("com.contentprovider.personprovider", "person/#", 2);}public static final Uri CONTENT_URI = Uri.parse("conten://com.contentprovider.personprovider/person");@Overridepublic int delete(Uri uri, String arg1, String[] arg2) {return 0;}@Overridepublic String getType(Uri uri) {switch (sMatcher.match(uri)) {case 1:return "vnd.android.cursor.dir/person"; // List of items.case 2:return "vnd.android.cursor.item/person"; // Specific item.default:return null;}}@Overridepublic Uri insert(Uri uri, ContentValues values) {try {Log.i("PersonContentProvider", "type" + getType(uri));Log.i("PersonContentProvider", "insert test...");} catch (Exception e) {e.printStackTrace();}return null;}@Overridepublic boolean onCreate() {return true;}@Overridepublic Cursor query(Uri uri, String[] arg1, String arg2, String[] arg3,String arg4) {// TODO Auto-generated method stubreturn null;}@Overridepublic int update(Uri uri, ContentValues arg1, String arg2, String[] arg3) {// TODO Auto-generated method stubreturn 0;}}//其他应用访问ContentProviderpublic class OutSideActivty extends Activity {    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        ContentValues values = new ContentValues();        values.put("name", "emily"); this.getContentResolver().insert(Uri.parse("content://com.contentprovider.personprovider/person"), values);        setContentView(R.layout.main);    }}

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