【移动应用开发技术】还没弄懂四大组件？带你全面解析ContentProvider篇

【移动应用开发技术】还没弄懂四大组件？带你全面解析ContentProvider篇

喜欢的小伙伴欢迎关注，我会定期分享Android知识点及解析，还会不断更新的BATJ面试专题，欢迎大家前来探讨交流，如有好的文章也欢迎投稿。1.什么是ContentProviderContentProvider，是自身APP开放给第三方APP的，用于访问自身数据库数据的接口。第三方APP可以通过该接口，对指定的数据进行增删改查。那么如何定义自身的ContentProvider接口呢？在回答问题之前，先来关注一下Uri。2.什么是Uri原因在于，uri是ContentProvider解析外部请求（或者说是，第三方访问自身数据库）的关键参数。Uri的字符串格式如下content://package/table/idcontent://package/table/id例如content://com.breakloop.sqlitehelperdemo/hero/1content://com.breakloop.sqlitehelperdemo/hero/1从上方Uri示例中，可以获取到以下信息。第三方APP想要访问com.breakloop.sqlitehelperdemo的数据库。至于哪个，由contentProvider内部映射指定。访问表hero。至于表名是不是真为hero，也由contentProvider说了算。访问id为1的数据。至于是不是id代表的具体含义，解释权也归contentProvider。那么，第三方APP将Uri传入后，ContentProvider如何将其map为具体的数据库操作呢？这便有了UriMatcher工具类的引入。3.UriMatcher该工具类，可以将Uri映射为int类型的行为代码。行为代码，可以看做是ContentProvider自定义的枚举类型。而不同的行为代码，绑定不同的数据库操作。我们先来看一下，Uri与行为代码的映射关系

public

final

static

String

AUTHORITY="com.breakloop.contentproviderdemo1";

public

final

static

int

BY_NAME=1;

public

final

static

int

BY_AGE=2;

public

final

static

int

BY_SEX=3;

public

final

static

int

BY_NONE=0;

public

final

static

String

PATH_BY_NAME=DBConst.TABLE_PERSON+"/ByName/*";

public

final

static

String

PATH_BY_AGE=DBConst.TABLE_PERSON+"/ByAge/#";

public

final

static

String

PATH_BY_SEX=DBConst.TABLE_PERSON+"/BySex/*";

}static

{

matcher=new

UriMatcher(UriMatcher.NO_MATCH);

matcher.addURI(MatcherConst.AUTHORITY,MatcherConst.PATH_BY_NAME,MatcherConst.BY_NAME);

matcher.addURI(MatcherConst.AUTHORITY,MatcherConst.PATH_BY_AGE,MatcherConst.BY_AGE);

matcher.addURI(MatcherConst.AUTHORITY,MatcherConst.PATH_BY_SEX,MatcherConst.BY_SEX);

matcher.addURI(MatcherConst.AUTHORITY,DBConst.TABLE_PERSON,MatcherConst.BY_NONE);

}在上面的示例中，UriMatch绑定了四个Uri，并将各个Uri映射为四个行为代码。其中，用到了转义符。#代表任意数字，*代表任意字母。那么如何将行为代码映射为具体的数据库操作呢？，换句话说，在哪儿使用UriMatcher呢？当然是ContentProvider中！！！在ContentProvider中的增删改查方法中，完成操作映射。我们来看一下，ContentProvider的创建。4.ContentProvider的创建先用AndroidStudio创建一个ContentProvider.创建过程中，需要提供AUTHORITY,ContentProvider生成后，AndroidStudio将自动帮助ContentProvider在Manifest中进行注册。接下来，我们看看ContentProvider的结构。5.ContentProvider的结构import

android.content.ContentProvider;import

android.content.ContentValues;import

android.content.UriMatcher;import

android.database.Cursor;import

.Uri;public

class

MyContentProvider

extends

ContentProvider

{

public

MyContentProvider()

{

}

@Override

public

int

delete(Uri

uri,

String

selection,

String[]

selectionArgs)

{

//

Implement

this

to

handle

requests

to

delete

one

or

more

rows.

throw

new

UnsupportedOperationException("Not

yet

implemented");

}

@Override

public

String

getType(Uri

uri)

{

//

TODO:

Implement

this

to

handle

requests

for

the

MIME

type

of

the

data

//

at

the

given

URI.

throw

new

UnsupportedOperationException("Not

yet

implemented");

}

@Override

public

Uri

insert(Uri

uri,

ContentValues

values)

{

//

TODO:

Implement

this

to

handle

requests

to

insert

a

new

row.

throw

new

UnsupportedOperationException("Not

yet

implemented");

}

@Override

public

boolean

onCreate()

{

//

TODO:

Implement

this

to

initialize

your

content

provider

on

startup.

return

false;

}

@Override

public

Cursor

query(Uri

uri,

String[]

projection,

String

selection,

String[]

selectionArgs,

String

sortOrder)

{

//

TODO:

Implement

this

to

handle

query

requests

from

clients.

throw

new

UnsupportedOperationException("Not

yet

implemented");

}

@Override

public

int

update(Uri

uri,

ContentValues

values,

String

selection,

String[]

selectionArgs)

{

//

TODO:

Implement

this

to

handle

requests

to

update

one

or

more

rows.

throw

new

UnsupportedOperationException("Not

yet

implemented");

}

}一共七个方法。包括一个构造方法，四个数据库方法（增删改查），一个初始化方法（onCreate）,还有一个getType。关于getType，我们之后解释。关于构造方法，没什么可解释的。关于初始化方法，当返回true时，表明初始化成功，否则，失败。由于我们要对数据库进行操作，因此，需要获取sqlite数据库对象。public

boolean

onCreate()

{

helper=new

mySqliteHelper(getContext(),DBConst.DB_NAME,null,1);

return

true;

}关于数据库方法，我们看到传参中存在Uri，因此，这里需要用到UirMatcher了。我们将刚才的UriMatcher代码段，加入MyContentProvider.这样，我们就可以在各个数据库方法中，解析Uri了。同时，由于sqlite数据库对象的存在，进而可以对数据库进行相应操作。6.行为代码Mapping数据库操作我们先看一下最简单的插入操作。

public

Uri

insert(Uri

uri,

ContentValues

values)

{

Uri

returnUri=null;

SQLiteDatabase

db=helper.getWritableDatabase();

switch

(matcher.match(uri)){

case

MatcherConst.BY_NONE:

long

recordID=db.insert(DBConst.TABLE_PERSON,null,values);

returnUri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/"+recordID);

break;

default:

break;

}

return

returnUri;

}再来看一下稍微复杂的查询。

public

Cursor

query(Uri

uri,

String[]

projection,

String

selection,

String[]

selectionArgs,

String

sortOrder)

{

Cursor

cursor=null;

SQLiteDatabase

db=helper.getReadableDatabase();

switch

(matcher.match(uri)){

case

MatcherConst.BY_NONE:

cursor=db.query(DBConst.TABLE_PERSON,projection,selection,selectionArgs,null,null,sortOrder);

break;

case

MatcherConst.BY_AGE:

cursor=db.query(DBConst.TABLE_PERSON,projection,DBConst.COLUMN_AGE+"=?",new

String[]{uri.getPathSegments().get(2)},null,null,sortOrder);

break;

case

MatcherConst.BY_SEX:

cursor=db.query(DBConst.TABLE_PERSON,projection,DBConst.COLUMN_SEX+"=?",new

String[]{uri.getPathSegments().get(2)},null,null,sortOrder);

break;

case

MatcherConst.BY_NAME:

cursor=db.query(DBConst.TABLE_PERSON,projection,DBConst.COLUMN_NAME+"=?",new

String[]{uri.getPathSegments().get(2)},null,null,sortOrder);

break;

default:

break;

}

return

cursor;

}这里需要注意的是，如何取Uri中的传入数据。使用的获取方法是uri.getPathSegments().get(index)。该方法获取的是AUTHORITY后面的String部分。然后，以”/”为分隔符，生成String[]。接着是更新操作。

@Override

public

int

update(Uri

uri,

ContentValues

values,

String

selection,

String[]

selectionArgs)

{

int

recordID=0;

SQLiteDatabase

db=helper.getWritableDatabase();

switch

(matcher.match(uri)){

case

MatcherConst.BY_NONE:

recordID=db.update(DBConst.TABLE_PERSON,values,null,null);

break;

case

MatcherConst.BY_AGE:

recordID=db.update(DBConst.TABLE_PERSON,values,DBConst.COLUMN_AGE+"=?",new

String[]{uri.getPathSegments().get(2)});

break;

case

MatcherConst.BY_SEX:

recordID=db.update(DBConst.TABLE_PERSON,values,DBConst.COLUMN_SEX+"=?",new

String[]{uri.getPathSegments().get(2)});

break;

case

MatcherConst.BY_NAME:

recordID=db.update(DBConst.TABLE_PERSON,values,DBConst.COLUMN_NAME+"=?",new

String[]{uri.getPathSegments().get(2)});

break;

default:

break;

}

return

recordID;

}还有删除。

public

int

delete(Uri

uri,

String

selection,

String[]

selectionArgs)

{

int

recordID=0;

SQLiteDatabase

db=helper.getWritableDatabase();

switch

(matcher.match(uri)){

case

MatcherConst.BY_NONE:

recordID=db.delete(DBConst.TABLE_PERSON,null,null);

break;

case

MatcherConst.BY_AGE:

recordID=db.delete(DBConst.TABLE_PERSON,DBConst.COLUMN_AGE+"=?",new

String[]{uri.getPathSegments().get(2)});

break;

case

MatcherConst.BY_SEX:

recordID=db.delete(DBConst.TABLE_PERSON,DBConst.COLUMN_SEX+"=?",new

String[]{uri.getPathSegments().get(2)});

break;

case

MatcherConst.BY_NAME:

recordID=db.delete(DBConst.TABLE_PERSON,DBConst.COLUMN_NAME+"=?",new

String[]{uri.getPathSegments().get(2)});

break;

default:

break;

}

return

recordID;

}那么，第三方如何调用ContentProvider呢？7.ContentProvider的使用这里，我们新建一个工程contentproviderdemo2，在必要的位置使用方法publicContentResolvergetContentResolver()publicContentResolvergetContentResolver()获取ContentProvider实例，之后便可传入Uri，调用数据库相关方法了。例如，我们插入四条记录。

Uri

returnUri=null;

ContentResolver

resolver=getContentResolver();

Uri

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);

ContentValues

values=new

ContentValues();

values.put(DBConst.COLUMN_NAME,"A");

values.put(DBConst.COLUMN_AGE,10);

values.put(DBConst.COLUMN_SEX,"Male");

returnUri=resolver.insert(uri,values);

if(returnUri!=null)

Log.i(TAG,

"return

Uri

=

"+returnUri.toString());

values.put(DBConst.COLUMN_NAME,"B");

values.put(DBConst.COLUMN_AGE,11);

values.put(DBConst.COLUMN_SEX,"Male");

returnUri=resolver.insert(uri,values);

if(returnUri!=null)

Log.i(TAG,

"return

Uri

=

"+returnUri.toString());

values.put(DBConst.COLUMN_NAME,"C");

values.put(DBConst.COLUMN_AGE,12);

values.put(DBConst.COLUMN_SEX,"Female");

returnUri=resolver.insert(uri,values);

if(returnUri!=null)

Log.i(TAG,

"return

Uri

=

"+returnUri.toString());

values.put(DBConst.COLUMN_NAME,"D");

values.put(DBConst.COLUMN_AGE,13);

values.put(DBConst.COLUMN_SEX,"Female");

returnUri=resolver.insert(uri,values);

if(returnUri!=null)

Log.i(TAG,

"return

Uri

=

"+returnUri.toString());我们看一下输出结果。I/com.breakloop.contentproviderdemo2.MainActivity:

return

Uri

=

content://com.breakloop.contentproviderdemo1/PERSON/1I/com.breakloop.contentproviderdemo2.MainActivity:

return

Uri

=

content://com.breakloop.contentproviderdemo1/PERSON/2I/com.breakloop.contentproviderdemo2.MainActivity:

return

Uri

=

content://com.breakloop.contentproviderdemo1/PERSON/3I/com.breakloop.contentproviderdemo2.MainActivity:

return

Uri

=

content://com.breakloop.contentproviderdemo1/PERSON/4既然，写入成功，那我们查询一下。

public

void

selectRecord(){

Uri

uri;

String

name="A";

int

age=11;

String

sex="Male";

Log.i(TAG,

"Select

by

Name");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/ByName/"+name);

selectRecord(uri);

Log.i(TAG,

"Select

by

Age");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/ByAge/"+age);

selectRecord(uri);

Log.i(TAG,

"Select

by

Sex");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/BySex/"+sex);

selectRecord(uri);

Log.i(TAG,

"Select

All");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);

selectRecord(uri);

}

private

void

selectRecord(Uri

uri){

Cursor

cursor;

cursor=resolver.query(uri,new

String[]{DBConst.COLUMN_AGE,

DBConst.COLUMN_NAME,

DBConst.COLUMN_SEX},null,null,null);

if(cursor!=null){

while(cursor.moveToNext()){

Log.i(TAG,

"name

=

"+cursor.getString(1)+

"

age

=

"+cursor.getInt(0)

+"

"+cursor.getString(2));

}

}

}输出结果如下I/com.breakloop.contentproviderdemo2.MainActivity:

Select

by

Name

I/com.breakloop.contentproviderdemo2.MainActivity:

name

=

A

age

=

10

Male

I/com.breakloop.contentproviderdemo2.MainActivity:

Select

by

Age

I/com.breakloop.contentproviderdemo2.MainActivity:

name

=

B

age

=

11

Male

I/com.breakloop.contentproviderdemo2.MainActivity:

Select

by

Sex

I/com.breakloop.contentproviderdemo2.MainActivity:

name

=

A

age

=

10

Male

I/com.breakloop.contentproviderdemo2.MainActivity:

name

=

B

age

=

11

Male

I/com.breakloop.contentproviderdemo2.MainActivity:

Select

All

I/com.breakloop.contentproviderdemo2.MainActivity:

name

=

A

age

=

10

Male

I/com.breakloop.contentproviderdemo2.MainActivity:

name

=

B

age

=

11

Male

I/com.breakloop.contentproviderdemo2.MainActivity:

name

=

C

age

=

12

Female

I/com.breakloop.contentproviderdemo2.MainActivity:

name

=

D

age

=

13

Female我们再来更新一下。

public

void

updateRecord(){

Uri

uri;

String

name="A";

int

age=11;

String

sex="Female";

ContentValues

values=new

ContentValues();

Log.i(TAG,

"Update

by

Name");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/ByName/"+name);

values.put(DBConst.COLUMN_NAME,name+name);

update(uri,values);

Log.i(TAG,

"Update

by

Age");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/ByAge/"+age);

values.clear();

values.put(DBConst.COLUMN_AGE,14);

update(uri,values);

Log.i(TAG,

"Update

by

Sex");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/BySex/"+sex);

values.clear();

values.put(DBConst.COLUMN_AGE,15);

update(uri,values);

Log.i(TAG,

"Update

All");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);

values.put(DBConst.COLUMN_SEX,"Male");

update(uri,values);

Log.i(TAG,

"Select

All");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);

selectRecord(uri);

}

private

void

update(Uri

uri,ContentValues

values){

int

count;

count=resolver.update(uri,values,null,null);

Log.i(TAG,

"update

"+count+"

record");

}结果如下I/com.breakloop.contentproviderdemo2.MainActivity:

Update

by

Name

I/com.breakloop.contentproviderdemo2.MainActivity:

update

1

record

I/com.breakloop.contentproviderdemo2.MainActivity:

Update

by

Age

I/com.breakloop.contentproviderdemo2.MainActivity:

update

1

record

I/com.breakloop.contentproviderdemo2.MainActivity:

Update

by

Sex

I/com.breakloop.contentproviderdemo2.MainActivity:

update

2

record

I/com.breakloop.contentproviderdemo2.MainActivity:

Update

All

I/com.breakloop.contentproviderdemo2.MainActivity:

update

4

record

I/com.breakloop.contentproviderdemo2.MainActivity:

Select

All

I/com.breakloop.contentproviderdemo2.MainActivity:

name

=

AA

age

=

15

Male

I/com.breakloop.contentproviderdemo2.MainActivity:

name

=

B

age

=

15

Male

I/com.breakloop.contentproviderdemo2.MainActivity:

name

=

C

age

=

15

Male

I/com.breakloop.contentproviderdemo2.MainActivity:

name

=

D

age

=

15

Male都不要了，删除！（这里是对更新前的数据库进行的操作）

public

void

deleteRecord(){

Uri

uri;

String

name="A";

int

age=11;

String

sex="Female";

Log.i(TAG,

"Delete

by

Name");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/ByName/"+name);

delete(uri);

Log.i(TAG,

"Select

All");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);

selectRecord(uri);

Log.i(TAG,

"Delete

by

Age");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/ByAge/"+age);

delete(uri);

Log.i(TAG,

"Select

All");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);

selectRecord(uri);

Log.i(TAG,

"Delete

by

Sex");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/BySex/"+sex);

delete(uri);

Log.i(TAG,

"Select

All");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);

selectRecord(uri);

Log.i(TAG,

"Delete

All");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);

delete(uri);

Log.i(TAG,

"Select

All");

uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);

selectRecord(uri);

}

private

void

delete(Uri

uri){

int

count;

count=resolver.delete(uri,null,null);

Log.i(TAG,

"delete

"+count+"

record");

}结果如下I/com.breakloop.contentproviderdemo2.MainActivity:

delete

1

record

I/com.breakloop.contentproviderdemo2.MainActivity:

Select

All

I/com.breakloop.contentproviderdemo2.MainActivity:

name

=

B

age

=

11

Male

I/com.breakloop.contentproviderdemo2.MainActivity:

name

=

C

age

=

12

Female

I/com.breakloop.contentproviderdemo2.MainActivity:

name

=

D

age

=

13

Female

I/com.breakloop.contentproviderdemo2.MainActivity:

Delete

by

Age

I/com.breakloop.contentproviderdemo2.MainActivity:

delete

1

record

I/com.breakloop.contentproviderdemo2.MainActivity:

Select

All

I/com.breakloop.contentproviderdemo2.MainActivity:

name

=

C

age

=

12

Female

I/com.breakloop.contentproviderdemo2.