【移動(dòng)應(yīng)用開發(fā)技術(shù)】還沒弄懂四大組件？帶你全面解析ContentProvider篇

【移動(dòng)應(yīng)用開發(fā)技術(shù)】還沒弄懂四大組件？帶你全面解析ContentProvider篇

喜歡的小伙伴歡迎關(guān)注，我會(huì)定期分享Android知識(shí)點(diǎn)及解析，還會(huì)不斷更新的BATJ面試專題，歡迎大家前來探討交流，如有好的文章也歡迎投稿。1.什么是ContentProviderContentProvider，是自身APP開放給第三方APP的，用于訪問自身數(shù)據(jù)庫(kù)數(shù)據(jù)的接口。第三方APP可以通過該接口，對(duì)指定的數(shù)據(jù)進(jìn)行增刪改查。那么如何定義自身的ContentProvider接口呢？在回答問題之前，先來關(guān)注一下Uri。2.什么是Uri原因在于，uri是ContentProvider解析外部請(qǐng)求（或者說是，第三方訪問自身數(shù)據(jù)庫(kù)）的關(guān)鍵參數(shù)。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從上方Uri示例中，可以獲取到以下信息。第三方APP想要訪問com.breakloop.sqlitehelperdemo的數(shù)據(jù)庫(kù)。至于哪個(gè)，由contentProvider內(nèi)部映射指定。訪問表hero。至于表名是不是真為hero，也由contentProvider說了算。訪問id為1的數(shù)據(jù)。至于是不是id代表的具體含義，解釋權(quán)也歸contentProvider。那么，第三方APP將Uri傳入后，ContentProvider如何將其map為具體的數(shù)據(jù)庫(kù)操作呢？這便有了UriMatcher工具類的引入。3.UriMatcher該工具類，可以將Uri映射為int類型的行為代碼。行為代碼，可以看做是ContentProvider自定義的枚舉類型。而不同的行為代碼，綁定不同的數(shù)據(jù)庫(kù)操作。我們先來看一下，Uri與行為代碼的映射關(guān)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綁定了四個(gè)Uri，并將各個(gè)Uri映射為四個(gè)行為代碼。其中，用到了轉(zhuǎn)義符。#代表任意數(shù)字，*代表任意字母。那么如何將行為代碼映射為具體的數(shù)據(jù)庫(kù)操作呢？，換句話說，在哪兒使用UriMatcher呢？當(dāng)然是ContentProvider中?。?！在ContentProvider中的增刪改查方法中，完成操作映射。我們來看一下，ContentProvider的創(chuàng)建。4.ContentProvider的創(chuàng)建先用AndroidStudio創(chuàng)建一個(gè)ContentProvider.創(chuàng)建過程中，需要提供AUTHORITY,ContentProvider生成后，AndroidStudio將自動(dòng)幫助ContentProvider在Manifest中進(jìn)行注冊(cè)。接下來，我們看看ContentProvider的結(jié)構(gòu)。5.ContentProvider的結(jié)構(gòu)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");

}

}一共七個(gè)方法。包括一個(gè)構(gòu)造方法，四個(gè)數(shù)據(jù)庫(kù)方法（增刪改查），一個(gè)初始化方法（onCreate）,還有一個(gè)getType。關(guān)于getType，我們之后解釋。關(guān)于構(gòu)造方法，沒什么可解釋的。關(guān)于初始化方法，當(dāng)返回true時(shí)，表明初始化成功，否則，失敗。由于我們要對(duì)數(shù)據(jù)庫(kù)進(jìn)行操作，因此，需要獲取sqlite數(shù)據(jù)庫(kù)對(duì)象。public

boolean

onCreate()

{

helper=new

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

return

true;

}關(guān)于數(shù)據(jù)庫(kù)方法，我們看到傳參中存在Uri，因此，這里需要用到UirMatcher了。我們將剛才的UriMatcher代碼段，加入MyContentProvider.這樣，我們就可以在各個(gè)數(shù)據(jù)庫(kù)方法中，解析Uri了。同時(shí)，由于sqlite數(shù)據(jù)庫(kù)對(duì)象的存在，進(jìn)而可以對(duì)數(shù)據(jù)庫(kù)進(jìn)行相應(yīng)操作。6.行為代碼Mapping數(shù)據(jù)庫(kù)操作我們先看一下最簡(jiǎn)單的插入操作。

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;

}再來看一下稍微復(fù)雜的查詢。

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;

}這里需要注意的是，如何取Uri中的傳入數(shù)據(jù)。使用的獲取方法是uri.getPathSegments().get(index)。該方法獲取的是AUTHORITY后面的String部分。然后，以”/”為分隔符，生成String[]。接著是更新操作。

@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;

}還有刪除。

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，第三方如何調(diào)用ContentProvider呢？7.ContentProvider的使用這里，我們新建一個(gè)工程contentproviderdemo2，在必要的位置使用方法publicContentResolvergetContentResolver()publicContentResolvergetContentResolver()獲取ContentProvider實(shí)例，之后便可傳入U(xiǎn)ri，調(diào)用數(shù)據(jù)庫(kù)相關(guān)方法了。例如，我們插入四條記錄。

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());我們看一下輸出結(jié)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，寫入成功，那我們查詢一下。

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));

}

}

}輸出結(jié)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我們?cè)賮砀乱幌隆?/p>

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");

}結(jié)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，刪除?。ㄟ@里是對(duì)更新前的數(shù)據(jù)庫(kù)進(jìn)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");

}結(jié)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.