【移動應用開發(fā)技術】Android中如何實現觀察者模式

【移動應用開發(fā)技術】Android中如何實現觀察者模式

概述模式中的角色/upload/information/20200623/125/123036.png觀察者模式示例public

class

MyPerson

extends

Observable

{

private

String

name;

private

int

age;

private

String

sex;

public

String

getName()

{

return

name;

}

public

void

setName(String

name)

{

=

name;

setChanged();

notifyObservers();

}

public

int

getAge()

{

return

age;

}

public

void

setAge(int

age)

{

this.age

=

age;

setChanged();

notifyObservers();

}

public

String

getSex()

{

return

sex;

}

public

void

setSex(String

sex)

{

this.sex

=

sex;

setChanged();

notifyObservers();

}

@Override

public

String

toString()

{

return

"MyPerson

[name="

+

name

+

",

age="

+

age

+

",

sex="

+

sex

+

"]";

}

}public

class

MyObserver

implements

Observer

{

private

int

id;

private

MyPerson

myPerson;

public

MyObserver(int

id)

{

System.out.println("我是觀察者>"

+

id);

this.id

=

id;

}

public

int

getId()

{

return

id;

}

public

void

setId(int

id)

{

this.id

=

id;

}

public

MyPerson

getMyPerson()

{

return

myPerson;

}

public

void

setMyPerson(MyPerson

myPerson)

{

this.myPerson

=

myPerson;

}

@Override

public

void

update(Observable

observable,

Object

data)

{

System.out.println("觀察者>"

+

id

+

"得到更新");

this.myPerson

=

(MyPerson)

observable;

System.out.println(((MyPerson)

observable).toString());

}

}public

class

MainActivity

extends

Activity

{

private

Button

btnAddObserver;

private

Button

btnChangeData;

private

MyPerson

observable;

private

MyObserver

myObserver;

private

List<MyObserver>

myObservers;

private

ListView

listview;

private

int

i;

private

Handler

handler

=

new

Handler()

{

public

void

handleMessage(android.os.Message

msg)

{

MyListAdapter

myListAdapter

=

new

MyListAdapter(MainActivity.this,

myObservers);

listview.setAdapter(myListAdapter);

};

};

@Override

protected

void

onCreate(Bundle

savedInstanceState)

{

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

btnAddObserver

=

(Button)

findViewById(R.id.btn_add_observer);

btnChangeData

=

(Button)

findViewById(R.id.btn_change_data);

listview

=

getListView();

observable

=

new

MyPerson();

myObservers

=

new

ArrayList<MyObserver>();

btnAddObserver.setOnClickListener(new

OnClickListener()

{

@Override

public

void

onClick(View

v)

{

myObserver

=

new

MyObserver(i);

i++;

observable.addObserver(myObserver);

myObservers.add(myObserver);

handler.sendEmptyMessage(0);

}

});

btnChangeData.setOnClickListener(new

OnClickListener()

{

@Override

public

void

onClick(View

v)

{

observable.setName("a"

+

i);

observable.setAge(10

+

i);

observable.setSex("男"

+

i);

handler.sendEmptyMessage(0);

}

});

}

@Override

protected

void

onDestroy()

{

//

TODO

Auto-generated

method

stub

super.onDestroy();

observable.deleteObserver(myObserver);

}

}Android源碼中的模式實現public

abstract

class

BaseAdapter

implements

ListAdapter,

SpinnerAdapter

{

//

數據集觀察者

private

final

DataSetObservable

mDataSetObservable

=

new

DataSetObservable();

//

代碼省略

public

void

registerDataSetObserver(DataSetObserver

observer)

{

mDataSetObservable.registerObserver(observer);

}

public

void

unregisterDataSetObserver(DataSetObserver

observer)

{

mDataSetObservable.unregisterObserver(observer);

}

/**

*

Notifies

the

attached

observers

that

the

underlying

data

has

been

changed

*

and

any

View

reflecting

the

data

set

should

refresh

itself.

*

當數據集用變化時通知所有觀察者

*/

public

void

notifyDataSetChanged()

{

mDataSetObservable.notifyChanged();

}

}public

class

DataSetObservable

extends

Observable<DataSetObserver>

{

/**

*

Invokes

onChanged

on

each

observer.

Called

when

the

data

set

being

observed

has

*

changed,

and

which

when

read

contains

the

new

state

of

the

data.

*/

public

void

notifyChanged()

{

synchronized(mObservers)

{

//

調用所有觀察者的onChanged方式

for

(int

i

=

mObservers.size()

-

1;

i

>=

0;

i--)

{

mObservers.get(i).onChanged();

}

}

}

}

@Override

public

void

setAdapter(ListAdapter

adapter)

{

//

如果已經有了一個adapter,那么先注銷該Adapter對應的觀察者

if

(mAdapter

!=

null

&&

mDataSetObserver

!=

null)

{

mAdapter.unregisterDataSetObserver(mDataSetObserver);

}

//

代碼省略

super.setAdapter(adapter);

if

(mAdapter

!=

null)

{

mAreAllItemsSelectable

=

mAdapter.areAllItemsEnabled();

mOldItemCount

=

mItemCount;

//

獲取數據的數量

mItemCount

=

mAdapter.getCount();

checkFocus();

//

注意這里

:

創(chuàng)建一個一個數據集觀察者

mDataSetObserver

=

new

AdapterDataSetObserver();

//

將這個觀察者注冊到Adapter中，實際上是注冊到DataSetObservable中

mAdapter.registerDataSetObserver(mDataSetObserver);

//

代碼省略

}

else

{

//

代碼省略

}

requestLayout();

}

class

AdapterDataSetObserver

extends

AdapterView<ListAdapter>.AdapterDataSetObserver

{

@Override

public

void

onChanged()

{

super.onChanged();

if

(mFastScroll

!=

null)

{

mFastScroll.onSectionsChanged();

}

}

@Override

public

void

onInvalidated()

{

super.onInvalidated();

if

(mFastScroll

!=

null)

{

mFastScroll.onSectionsChanged();

}

}

}class

AdapterDataSetObserver

extends

DataSetObserver

{

private

Parcelable

mInstanceState

=

null;

//

調用Adapter的notifyDataSetChanged的時候會調用所有觀察者的onChanged方法,核心實現就在這里

@Override

public

void

onChanged()

{

mDataChanged

=

true;

mOldItemCount

=

mItemCount;

//

獲取Adapter中數據的數量

mIt