存储方式之ContentProvider

开始学习之前先回忆一下android的几种存储方式：

SharedPreference

ContentProvider

SQLite数据库

文件存储

sdCard存储

这几种是我记忆中的5中存储方式。最喜欢的也是用的最多的是SharedPreference简单方便。然后就是数据库，因为用的多，不得不喜欢呀。一直让我很纠结的就是今天学习的ContentProvider。原因？因为用的少呀（其实是没用过）。因为项目里不需要用，也就只是了解一下，没有去研究过，今天又时间，学习了一下，赶紧记录下来，好记性不如烂笔头呀！

　　ContentProvider的几个要点：

定义基本字段

在manifest里添加（provider和在需要用的activity里添加两个新的minetype）

继承ContentProvider

下面是代码：

　　1.定义基本字段

public class NotePad {
public static final String AUTHORITY = "com.google.provider.NotePad";    //ContentProvider的uri

public NotePad(){}

//定义基本字段
public static final class Notes implements BaseColumns{
public Notes(){}
//这里notes跟数据库里表名相同（我是这么认为的，不知道可不可以不一样，回头改改试试看）
public static final Uri CONTENT_URI    = Uri.parse("content://" + AUTHORITY + "/notes");

//新的MIME类型-多个
public static final String CONTENT_TYPE = "vnd.android.cursor.dir/vnd.google.note";

// 新的MIME类型-单个
public static final String CONTENT_ITEM_TYPE = "vnd.android.cursor.item/vnd.google.note";

public static final String    DEFAULT_SORT_ORDER    = "modified DESC";

//字段
public static final String    TITLE                = "title";
public static final String    NOTE                = "note";
public static final String    CREATEDDATE            = "created";
public static final String    MODIFIEDDATE        = "modified";
}
}

　　2.在manifest里添加（provider和在需要用的activity里添加两个新的minetype）

<activity
android:label="@string/app_name"
android:name="contentPro.DataProviderActivity" >
<intent-filter >
<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
<intent-filter>
<data android:mimeType="vnd.android.cursor.dir/vnd.google.note"/>
</intent-filter>
<intent-filter>
<data android:mimeType="vnd.android.cursor.item/vnd.google.note"/>
</intent-filter>
</activity>

<provider android:name="contentPro.NotePadProvider" android:authorities="com.google.provider.NotePad"/>

　

　3.继承ContentProvider

public class NotePadProvider extends ContentProvider {
private static final String TAG = "NotePadProvider";
// 数据库名
private static final String DATABASE_NAME = "note_pad.db";
private static final int DATABASE_VERSION = 2;
// 表名
private static final String NOTES_TABLE_NAME = "notes";
private static HashMap<String, String> sNotesProjectionMap;
private static final int NOTES = 1;
private static final int NOTE_ID = 2;
private static final UriMatcher sUriMatcher;
private DatabaseHelper mOpenHelper;
// 创建表SQL语句
private static final String CREATE_TABLE = "CREATE TABLE "
+ NOTES_TABLE_NAME + " (" + Notes._ID + " INTEGER PRIMARY KEY,"
+ Notes.TITLE + " TEXT," + Notes.NOTE + " TEXT,"
+ Notes.CREATEDDATE + " INTEGER," + Notes.MODIFIEDDATE + " INTEGER"
+ ");";

static {
sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
sUriMatcher.addURI(NotePad.AUTHORITY, "notes", NOTES);
sUriMatcher.addURI(NotePad.AUTHORITY, "notes/#", NOTE_ID);

sNotesProjectionMap = new HashMap<String, String>();
sNotesProjectionMap.put(Notes._ID, Notes._ID);
sNotesProjectionMap.put(Notes.TITLE, Notes.TITLE);
sNotesProjectionMap.put(Notes.NOTE, Notes.NOTE);
sNotesProjectionMap.put(Notes.CREATEDDATE, Notes.CREATEDDATE);
sNotesProjectionMap.put(Notes.MODIFIEDDATE, Notes.MODIFIEDDATE);
}

private static class DatabaseHelper extends SQLiteOpenHelper {
// 构造函数-创建数据库
DatabaseHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

// 创建表
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_TABLE);
}

// 更新数据库
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS notes");
onCreate(db);
}
}

@Override
public boolean onCreate() {
mOpenHelper = new DatabaseHelper(getContext());
return true;
}

@Override
// 查询操作
public Cursor query(Uri uri, String[] projection, String selection,
String[] selectionArgs, String sortOrder) {
SQLiteQueryBuilder qb = new SQLiteQueryBuilder();
switch (sUriMatcher.match(uri)) {
case NOTES:
qb.setTables(NOTES_TABLE_NAME);
qb.setProjectionMap(sNotesProjectionMap);
break;

case NOTE_ID:
qb.setTables(NOTES_TABLE_NAME);
qb.setProjectionMap(sNotesProjectionMap);
qb.appendWhere(Notes._ID + "=" + uri.getPathSegments().get(1));
break;

default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
String orderBy;
if (TextUtils.isEmpty(sortOrder)) {
orderBy = NotePad.Notes.DEFAULT_SORT_ORDER;
} else {
orderBy = sortOrder;
}
SQLiteDatabase db = mOpenHelper.getReadableDatabase();
Cursor c = qb.query(db, projection, selection, selectionArgs, null,
null, orderBy);
c.setNotificationUri(getContext().getContentResolver(), uri);
return c;
}

@Override
// 如果有自定义类型，必须实现该方法
public String getType(Uri uri) {
switch (sUriMatcher.match(uri)) {
case NOTES:
return Notes.CONTENT_TYPE;

case NOTE_ID:
return Notes.CONTENT_ITEM_TYPE;

default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
}

@Override
// 插入数据库
public Uri insert(Uri uri, ContentValues initialValues) {
if (sUriMatcher.match(uri) != NOTES) {
throw new IllegalArgumentException("Unknown URI " + uri);
}
ContentValues values;
if (initialValues != null) {
values = new ContentValues(initialValues);
} else {
values = new ContentValues();
}
Long now = Long.valueOf(System.currentTimeMillis());

if (values.containsKey(NotePad.Notes.CREATEDDATE) == false) {
values.put(NotePad.Notes.CREATEDDATE, now);
}
if (values.containsKey(NotePad.Notes.MODIFIEDDATE) == false) {
values.put(NotePad.Notes.MODIFIEDDATE, now);
}
if (values.containsKey(NotePad.Notes.TITLE) == false) {
Resources r = Resources.getSystem();
values.put(NotePad.Notes.TITLE,
r.getString(android.R.string.untitled));
}
if (values.containsKey(NotePad.Notes.NOTE) == false) {
values.put(NotePad.Notes.NOTE, "");
}
SQLiteDatabase db = mOpenHelper.getWritableDatabase();
long rowId = db.insert(NOTES_TABLE_NAME, Notes.NOTE, values);
if (rowId > 0) {
Uri noteUri = ContentUris.withAppendedId(NotePad.Notes.CONTENT_URI,
rowId);
getContext().getContentResolver().notifyChange(noteUri, null);
return noteUri;
}
throw new SQLException("Failed to insert row into " + uri);
}

@Override
// 删除数据
public int delete(Uri uri, String where, String[] whereArgs) {
SQLiteDatabase db = mOpenHelper.getWritableDatabase();
int count;
switch (sUriMatcher.match(uri)) {
case NOTES:
count = db.delete(NOTES_TABLE_NAME, where, whereArgs);
break;

case NOTE_ID:
String noteId = uri.getPathSegments().get(1);
count = db.delete(NOTES_TABLE_NAME,
Notes._ID
+ "="
+ noteId
+ (!TextUtils.isEmpty(where) ? " AND (" + where
+ ')' : ""), whereArgs);
break;

default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
getContext().getContentResolver().notifyChange(uri, null);
return count;
}

@Override
// 更新数据
public int update(Uri uri, ContentValues values, String where,
String[] whereArgs) {
SQLiteDatabase db = mOpenHelper.getWritableDatabase();
int count;
switch (sUriMatcher.match(uri)) {
case NOTES:
count = db.update(NOTES_TABLE_NAME, values, where, whereArgs);
break;

case NOTE_ID:
String noteId = uri.getPathSegments().get(1);
count = db.update(NOTES_TABLE_NAME, values,
Notes._ID
+ "="
+ noteId
+ (!TextUtils.isEmpty(where) ? " AND (" + where
+ ')' : ""), whereArgs);
break;

default:
throw new IllegalArgumentException("Unknown URI " + uri);
}
getContext().getContentResolver().notifyChange(uri, null);
return count;
}
}

4.应用

public class DataProviderActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

//插入数据
ContentValues values = new ContentValues();
values.put(NotePad.Notes.TITLE, "title1");
values.put(NotePad.Notes.NOTE, "NoteNote1");
getContentResolver().insert(NotePad.Notes.CONTENT_URI, values);

values.clear();
values.put(NotePad.Notes.TITLE, "title2");
values.put(NotePad.Notes.NOTE, "NoteNote2");
getContentResolver().insert(NotePad.Notes.CONTENT_URI, values);

/* 显示 */
displayNote();
}

private void displayNote() {
// TODO Auto-generated method stub
String columns[] = new String[]{
NotePad.Notes._ID,
NotePad.Notes.TITLE,
NotePad.Notes.NOTE,
NotePad.Notes.CREATEDDATE,
NotePad.Notes.MODIFIEDDATE
};
Uri myUri = NotePad.Notes.CONTENT_URI;
Cursor cursor = this.managedQuery(myUri, columns, null, null, null);
if (cursor.moveToFirst()) {
String id = null;
String title = null;

do{
id = cursor.getString(cursor.getColumnIndex(NotePad.Notes._ID));
title = cursor.getString(cursor.getColumnIndex(NotePad.Notes.TITLE));
Toast toast=Toast.makeText(this, "TITLE："+id + "NOTE：" + title, Toast.LENGTH_LONG);
toast.setGravity(Gravity.TOP|Gravity.CENTER, 0, 40);
toast.show();
}while(cursor.moveToNext());
}
}
}

以上代码来源：/article/1393376.html

感谢yinyuan1987 代码很易懂！