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");

	@Override
	public int delete(Uri uri, String arg1, String[] arg2) {

		return 0;
	}

	@Override
	public 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;
		}
	}

	@Override
	public 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;
	}

	@Override
	public boolean onCreate() {
		return true;
	}

	@Override
	public Cursor query(Uri uri, String[] arg1, String arg2, String[] arg3,
			String arg4) {
		// TODO Auto-generated method stub
		return null;
	}

	@Override
	public int update(Uri uri, ContentValues arg1, String arg2, String[] arg3) {
		// TODO Auto-generated method stub
		return 0;
	}

}

//其他应用访问ContentProvider
public 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);
    }
}