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Android GridView LruCache
小編覺(jué)得挺不錯(cuò)的,現(xiàn)在分享給大家,幫大家做個(gè)參考.
照片墻這種功能現(xiàn)在應(yīng)該算是挺常見(jiàn)了，在很多應(yīng)用中你都可以經(jīng)常看到照片墻的身影。它的設(shè)計(jì)思路其實(shí)也非常簡(jiǎn)單，用一個(gè)GridView控件當(dāng)作“墻”，然后隨著GridView的滾動(dòng)將一張張照片貼在“墻”上，這些照片可以是手機(jī)本地中存儲(chǔ)的，也可以是從網(wǎng)上下載的。制作類似于這種的功能的應(yīng)用，有一個(gè)非常重要的問(wèn)題需要考慮，就是圖片資源何時(shí)應(yīng)該釋放。因?yàn)殡S著GridView的滾動(dòng)，加載的圖片可能會(huì)越來(lái)越多，如果沒(méi)有一種合理的機(jī)制對(duì)圖片進(jìn)行釋放，那么當(dāng)圖片達(dá)到一定上限時(shí)，程序就必然會(huì)崩潰。
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今天我們照片墻應(yīng)用的實(shí)現(xiàn)，重點(diǎn)也是放在了如何防止由于圖片過(guò)多導(dǎo)致程序崩潰上面。主要的核心算法使用了Android中提供的LruCache類，這個(gè)類是3.1版本中提供的，如果你是在更早的Android版本中開(kāi)發(fā)，則需要導(dǎo)入android-support-v4的jar包。
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關(guān)于LruCache用法的詳細(xì)講解，可以參考Android高效加載大圖、多圖方案，有效避免程序OOM。
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那我們開(kāi)始動(dòng)手吧，新建一個(gè)Android項(xiàng)目，起名叫PhotoWallDemo，這里我使用的是Android 4.0的API。
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第一個(gè)要考慮的問(wèn)題就是，我們從哪兒去收集這么多的圖片呢？這里我從谷歌官方提供的Demo里將圖片源取了出來(lái)，我們就從這些網(wǎng)址中下載圖片，代碼如下所示：
[java]?view plaincopy
public?class?Images?{????????public?final?static?String[]?imageThumbUrls?=?new?String[]?{?? ????????????"https://lh6.googleusercontent.com/-55osAWw3x0Q/URquUtcFr5I/AAAAAAAAAbs/rWlj1RUKrYI/s160-c/A%252520Photographer.jpg",?? ????????????"https://lh4.googleusercontent.com/--dq8niRp7W4/URquVgmXvgI/AAAAAAAAAbs/-gnuLQfNnBA/s160-c/A%252520Song%252520of%252520Ice%252520and%252520Fire.jpg",?? ????????????"https://lh5.googleusercontent.com/-7qZeDtRKFKc/URquWZT1gOI/AAAAAAAAAbs/hqWgteyNXsg/s160-c/Another%252520Rockaway%252520Sunset.jpg",?? ????????????"https://lh3.googleusercontent.com/--L0Km39l5J8/URquXHGcdNI/AAAAAAAAAbs/3ZrSJNrSomQ/s160-c/Antelope%252520Butte.jpg",?? ????????????"https://lh6.googleusercontent.com/-8HO-4vIFnlw/URquZnsFgtI/AAAAAAAAAbs/WT8jViTF7vw/s160-c/Antelope%252520Hallway.jpg",?? ????????????"https://lh4.googleusercontent.com/-WIuWgVcU3Qw/URqubRVcj4I/AAAAAAAAAbs/YvbwgGjwdIQ/s160-c/Antelope%252520Walls.jpg",?? ????????????"https://lh6.googleusercontent.com/-UBmLbPELvoQ/URqucCdv0kI/AAAAAAAAAbs/IdNhr2VQoQs/s160-c/Apre%2525CC%252580s%252520la%252520Pluie.jpg",?? ????????????"https://lh3.googleusercontent.com/-s-AFpvgSeew/URquc6dF-JI/AAAAAAAAAbs/Mt3xNGRUd68/s160-c/Backlit%252520Cloud.jpg",?? ????????????"https://lh5.googleusercontent.com/-bvmif9a9YOQ/URquea3heHI/AAAAAAAAAbs/rcr6wyeQtAo/s160-c/Bee%252520and%252520Flower.jpg",?? ????????????"https://lh5.googleusercontent.com/-n7mdm7I7FGs/URqueT_BT-I/AAAAAAAAAbs/9MYmXlmpSAo/s160-c/Bonzai%252520Rock%252520Sunset.jpg",?? ????????????"https://lh6.googleusercontent.com/-4CN4X4t0M1k/URqufPozWzI/AAAAAAAAAbs/8wK41lg1KPs/s160-c/Caterpillar.jpg",?? ????????????"https://lh3.googleusercontent.com/-rrFnVC8xQEg/URqufdrLBaI/AAAAAAAAAbs/s69WYy_fl1E/s160-c/Chess.jpg",?? ????????????"https://lh5.googleusercontent.com/-WVpRptWH8Yw/URqugh-QmDI/AAAAAAAAAbs/E-MgBgtlUWU/s160-c/Chihuly.jpg",?? ????????????"https://lh5.googleusercontent.com/-0BDXkYmckbo/URquhKFW84I/AAAAAAAAAbs/ogQtHCTk2JQ/s160-c/Closed%252520Door.jpg",?? ????????????"https://lh3.googleusercontent.com/-PyggXXZRykM/URquh-kVvoI/AAAAAAAAAbs/hFtDwhtrHHQ/s160-c/Colorado%252520River%252520Sunset.jpg",?? ????????????"https://lh3.googleusercontent.com/-ZAs4dNZtALc/URquikvOCWI/AAAAAAAAAbs/DXz4h3dll1Y/s160-c/Colors%252520of%252520Autumn.jpg",?? ????????????"https://lh4.googleusercontent.com/-GztnWEIiMz8/URqukVCU7bI/AAAAAAAAAbs/jo2Hjv6MZ6M/s160-c/Countryside.jpg",?? ????????????"https://lh4.googleusercontent.com/-bEg9EZ9QoiM/URquklz3FGI/AAAAAAAAAbs/UUuv8Ac2BaE/s160-c/Death%252520Valley%252520-%252520Dunes.jpg",?? ????????????"https://lh6.googleusercontent.com/-ijQJ8W68tEE/URqulGkvFEI/AAAAAAAAAbs/zPXvIwi_rFw/s160-c/Delicate%252520Arch.jpg",?? ????????????"https://lh5.googleusercontent.com/-Oh8mMy2ieng/URqullDwehI/AAAAAAAAAbs/TbdeEfsaIZY/s160-c/Despair.jpg",?? ????????????"https://lh5.googleusercontent.com/-gl0y4UiAOlk/URqumC_KjBI/AAAAAAAAAbs/PM1eT7dn4oo/s160-c/Eagle%252520Fall%252520Sunrise.jpg",?? ????????????"https://lh3.googleusercontent.com/-hYYHd2_vXPQ/URqumtJa9eI/AAAAAAAAAbs/wAalXVkbSh0/s160-c/Electric%252520Storm.jpg",?? ????????????"https://lh5.googleusercontent.com/-PyY_yiyjPTo/URqunUOhHFI/AAAAAAAAAbs/azZoULNuJXc/s160-c/False%252520Kiva.jpg",?? ????????????"https://lh6.googleusercontent.com/-PYvLVdvXywk/URqunwd8hfI/AAAAAAAAAbs/qiMwgkFvf6I/s160-c/Fitzgerald%252520Streaks.jpg",?? ????????????"https://lh4.googleusercontent.com/-KIR_UobIIqY/URquoCZ9SlI/AAAAAAAAAbs/Y4d4q8sXu4c/s160-c/Foggy%252520Sunset.jpg",?? ????????????"https://lh6.googleusercontent.com/-9lzOk_OWZH0/URquoo4xYoI/AAAAAAAAAbs/AwgzHtNVCwU/s160-c/Frantic.jpg",?? ????????????"https://lh3.googleusercontent.com/-0X3JNaKaz48/URqupH78wpI/AAAAAAAAAbs/lHXxu_zbH8s/s160-c/Golden%252520Gate%252520Afternoon.jpg",?? ????????????"https://lh6.googleusercontent.com/-95sb5ag7ABc/URqupl95RDI/AAAAAAAAAbs/g73R20iVTRA/s160-c/Golden%252520Gate%252520Fog.jpg",?? ????????????"https://lh3.googleusercontent.com/-JB9v6rtgHhk/URqup21F-zI/AAAAAAAAAbs/64Fb8qMZWXk/s160-c/Golden%252520Grass.jpg",?? ????????????"https://lh4.googleusercontent.com/-EIBGfnuLtII/URquqVHwaRI/AAAAAAAAAbs/FA4McV2u8VE/s160-c/Grand%252520Teton.jpg",?? ????????????"https://lh4.googleusercontent.com/-WoMxZvmN9nY/URquq1v2AoI/AAAAAAAAAbs/grj5uMhL6NA/s160-c/Grass%252520Closeup.jpg",?? ????????????"https://lh3.googleusercontent.com/-6hZiEHXx64Q/URqurxvNdqI/AAAAAAAAAbs/kWMXM3o5OVI/s160-c/Green%252520Grass.jpg",?? ????????????"https://lh5.googleusercontent.com/-6LVb9OXtQ60/URquteBFuKI/AAAAAAAAAbs/4F4kRgecwFs/s160-c/Hanging%252520Leaf.jpg",?? ????????????"https://lh4.googleusercontent.com/-zAvf__52ONk/URqutT_IuxI/AAAAAAAAAbs/D_bcuc0thoU/s160-c/Highway%2525201.jpg",?? ????????????"https://lh6.googleusercontent.com/-H4SrUg615rA/URquuL27fXI/AAAAAAAAAbs/4aEqJfiMsOU/s160-c/Horseshoe%252520Bend%252520Sunset.jpg",?? ????????????"https://lh4.googleusercontent.com/-JhFi4fb_Pqw/URquuX-QXbI/AAAAAAAAAbs/IXpYUxuweYM/s160-c/Horseshoe%252520Bend.jpg",?? ????????????"https://lh5.googleusercontent.com/-UGgssvFRJ7g/URquueyJzGI/AAAAAAAAAbs/yYIBlLT0toM/s160-c/Into%252520the%252520Blue.jpg",?? ????????????"https://lh3.googleusercontent.com/-CH7KoupI7uI/URquu0FF__I/AAAAAAAAAbs/R7GDmI7v_G0/s160-c/Jelly%252520Fish%2525202.jpg",?? ????????????"https://lh4.googleusercontent.com/-pwuuw6yhg8U/URquvPxR3FI/AAAAAAAAAbs/VNGk6f-tsGE/s160-c/Jelly%252520Fish%2525203.jpg",?? ????????????"https://lh5.googleusercontent.com/-GoUQVw1fnFw/URquv6xbC0I/AAAAAAAAAbs/zEUVTQQ43Zc/s160-c/Kauai.jpg",?? ????????????"https://lh6.googleusercontent.com/-8QdYYQEpYjw/URquwvdh88I/AAAAAAAAAbs/cktDy-ysfHo/s160-c/Kyoto%252520Sunset.jpg",?? ????????????"https://lh4.googleusercontent.com/-vPeekyDjOE0/URquwzJ28qI/AAAAAAAAAbs/qxcyXULsZrg/s160-c/Lake%252520Tahoe%252520Colors.jpg",?? ????????????"https://lh4.googleusercontent.com/-xBPxWpD4yxU/URquxWHk8AI/AAAAAAAAAbs/ARDPeDYPiMY/s160-c/Lava%252520from%252520the%252520Sky.jpg",?? ????????????"https://lh3.googleusercontent.com/-897VXrJB6RE/URquxxxd-5I/AAAAAAAAAbs/j-Cz4T4YvIw/s160-c/Leica%25252050mm%252520Summilux.jpg",?? ????????????"https://lh5.googleusercontent.com/-qSJ4D4iXzGo/URquyDWiJ1I/AAAAAAAAAbs/k2pBXeWehOA/s160-c/Leica%25252050mm%252520Summilux.jpg",?? ????????????"https://lh6.googleusercontent.com/-dwlPg83vzLg/URquylTVuFI/AAAAAAAAAbs/G6SyQ8b4YsI/s160-c/Leica%252520M8%252520%252528Front%252529.jpg",?? ????????????"https://lh3.googleusercontent.com/-R3_EYAyJvfk/URquzQBv8eI/AAAAAAAAAbs/b9xhpUM3pEI/s160-c/Light%252520to%252520Sand.jpg",?? ????????????"https://lh3.googleusercontent.com/-fHY5h67QPi0/URqu0Cp4J1I/AAAAAAAAAbs/0lG6m94Z6vM/s160-c/Little%252520Bit%252520of%252520Paradise.jpg",?? ????????????"https://lh5.googleusercontent.com/-TzF_LwrCnRM/URqu0RddPOI/AAAAAAAAAbs/gaj2dLiuX0s/s160-c/Lone%252520Pine%252520Sunset.jpg",?? ????????????"https://lh3.googleusercontent.com/-4HdpJ4_DXU4/URqu046dJ9I/AAAAAAAAAbs/eBOodtk2_uk/s160-c/Lonely%252520Rock.jpg",?? ????????????"https://lh6.googleusercontent.com/-erbF--z-W4s/URqu1ajSLkI/AAAAAAAAAbs/xjDCDO1INzM/s160-c/Longue%252520Vue.jpg",?? ????????????"https://lh6.googleusercontent.com/-0CXJRdJaqvc/URqu1opNZNI/AAAAAAAAAbs/PFB2oPUU7Lk/s160-c/Look%252520Me%252520in%252520the%252520Eye.jpg",?? ????????????"https://lh3.googleusercontent.com/-D_5lNxnDN6g/URqu2Tk7HVI/AAAAAAAAAbs/p0ddca9W__Y/s160-c/Lost%252520in%252520a%252520Field.jpg",?? ????????????"https://lh6.googleusercontent.com/-flsqwMrIk2Q/URqu24PcmjI/AAAAAAAAAbs/5ocIH85XofM/s160-c/Marshall%252520Beach%252520Sunset.jpg",?? ????????????"https://lh4.googleusercontent.com/-Y4lgryEVTmU/URqu28kG3gI/AAAAAAAAAbs/OjXpekqtbJ4/s160-c/Mono%252520Lake%252520Blue.jpg",?? ????????????"https://lh4.googleusercontent.com/-AaHAJPmcGYA/URqu3PIldHI/AAAAAAAAAbs/lcTqk1SIcRs/s160-c/Monument%252520Valley%252520Overlook.jpg",?? ????????????"https://lh4.googleusercontent.com/-vKxfdQ83dQA/URqu31Yq_BI/AAAAAAAAAbs/OUoGk_2AyfM/s160-c/Moving%252520Rock.jpg",?? ????????????"https://lh5.googleusercontent.com/-CG62QiPpWXg/URqu4ia4vRI/AAAAAAAAAbs/0YOdqLAlcAc/s160-c/Napali%252520Coast.jpg",?? ????????????"https://lh6.googleusercontent.com/-wdGrP5PMmJQ/URqu5PZvn7I/AAAAAAAAAbs/m0abEcdPXe4/s160-c/One%252520Wheel.jpg",?? ????????????"https://lh6.googleusercontent.com/-6WS5DoCGuOA/URqu5qx1UgI/AAAAAAAAAbs/giMw2ixPvrY/s160-c/Open%252520Sky.jpg",?? ????????????"https://lh6.googleusercontent.com/-u8EHKj8G8GQ/URqu55sM6yI/AAAAAAAAAbs/lIXX_GlTdmI/s160-c/Orange%252520Sunset.jpg",?? ????????????"https://lh6.googleusercontent.com/-74Z5qj4bTDE/URqu6LSrJrI/AAAAAAAAAbs/XzmVkw90szQ/s160-c/Orchid.jpg",?? ????????????"https://lh6.googleusercontent.com/-lEQE4h6TePE/URqu6t_lSkI/AAAAAAAAAbs/zvGYKOea_qY/s160-c/Over%252520there.jpg",?? ????????????"https://lh5.googleusercontent.com/-cauH-53JH2M/URqu66v_USI/AAAAAAAAAbs/EucwwqclfKQ/s160-c/Plumes.jpg",?? ????????????"https://lh3.googleusercontent.com/-eDLT2jHDoy4/URqu7axzkAI/AAAAAAAAAbs/iVZE-xJ7lZs/s160-c/Rainbokeh.jpg",?? ????????????"https://lh5.googleusercontent.com/-j1NLqEFIyco/URqu8L1CGcI/AAAAAAAAAbs/aqZkgX66zlI/s160-c/Rainbow.jpg",?? ????????????"https://lh5.googleusercontent.com/-DRnqmK0t4VU/URqu8XYN9yI/AAAAAAAAAbs/LgvF_592WLU/s160-c/Rice%252520Fields.jpg",?? ????????????"https://lh3.googleusercontent.com/-hwh1v3EOGcQ/URqu8qOaKwI/AAAAAAAAAbs/IljRJRnbJGw/s160-c/Rockaway%252520Fire%252520Sky.jpg",?? ????????????"https://lh5.googleusercontent.com/-wjV6FQk7tlk/URqu9jCQ8sI/AAAAAAAAAbs/RyYUpdo-c9o/s160-c/Rockaway%252520Flow.jpg",?? ????????????"https://lh6.googleusercontent.com/-6cAXNfo7D20/URqu-BdzgPI/AAAAAAAAAbs/OmsYllzJqwo/s160-c/Rockaway%252520Sunset%252520Sky.jpg",?? ????????????"https://lh3.googleusercontent.com/-sl8fpGPS-RE/URqu_BOkfgI/AAAAAAAAAbs/Dg2Fv-JxOeg/s160-c/Russian%252520Ridge%252520Sunset.jpg",?? ????????????"https://lh6.googleusercontent.com/-gVtY36mMBIg/URqu_q91lkI/AAAAAAAAAbs/3CiFMBcy5MA/s160-c/Rust%252520Knot.jpg",?? ????????????"https://lh6.googleusercontent.com/-GHeImuHqJBE/URqu_FKfVLI/AAAAAAAAAbs/axuEJeqam7Q/s160-c/Sailing%252520Stones.jpg",?? ????????????"https://lh3.googleusercontent.com/-hBbYZjTOwGc/URqu_ycpIrI/AAAAAAAAAbs/nAdJUXnGJYE/s160-c/Seahorse.jpg",?? ????????????"https://lh3.googleusercontent.com/-Iwi6-i6IexY/URqvAYZHsVI/AAAAAAAAAbs/5ETWl4qXsFE/s160-c/Shinjuku%252520Street.jpg",?? ????????????"https://lh6.googleusercontent.com/-amhnySTM_MY/URqvAlb5KoI/AAAAAAAAAbs/pFCFgzlKsn0/s160-c/Sierra%252520Heavens.jpg",?? ????????????"https://lh5.googleusercontent.com/-dJgjepFrYSo/URqvBVJZrAI/AAAAAAAAAbs/v-F5QWpYO6s/s160-c/Sierra%252520Sunset.jpg",?? ????????????"https://lh4.googleusercontent.com/-Z4zGiC5nWdc/URqvBdEwivI/AAAAAAAAAbs/ZRZR1VJ84QA/s160-c/Sin%252520Lights.jpg",?? ????????????"https://lh4.googleusercontent.com/-_0cYiWW8ccY/URqvBz3iM4I/AAAAAAAAAbs/9N_Wq8MhLTY/s160-c/Starry%252520Lake.jpg",?? ????????????"https://lh3.googleusercontent.com/-A9LMoRyuQUA/URqvCYx_JoI/AAAAAAAAAbs/s7sde1Bz9cI/s160-c/Starry%252520Night.jpg",?? ????????????"https://lh3.googleusercontent.com/-KtLJ3k858eY/URqvC_2h_bI/AAAAAAAAAbs/zzEBImwDA_g/s160-c/Stream.jpg",?? ????????????"https://lh5.googleusercontent.com/-dFB7Lad6RcA/URqvDUftwWI/AAAAAAAAAbs/BrhoUtXTN7o/s160-c/Strip%252520Sunset.jpg",?? ????????????"https://lh5.googleusercontent.com/-at6apgFiN20/URqvDyffUZI/AAAAAAAAAbs/clABCx171bE/s160-c/Sunset%252520Hills.jpg",?? ????????????"https://lh4.googleusercontent.com/-7-EHhtQthII/URqvEYTk4vI/AAAAAAAAAbs/QSJZoB3YjVg/s160-c/Tenaya%252520Lake%2525202.jpg",?? ????????????"https://lh6.googleusercontent.com/-8MrjV_a-Pok/URqvFC5repI/AAAAAAAAAbs/9inKTg9fbCE/s160-c/Tenaya%252520Lake.jpg",?? ????????????"https://lh5.googleusercontent.com/-B1HW-z4zwao/URqvFWYRwUI/AAAAAAAAAbs/8Peli53Bs8I/s160-c/The%252520Cave%252520BW.jpg",?? ????????????"https://lh3.googleusercontent.com/-PO4E-xZKAnQ/URqvGRqjYkI/AAAAAAAAAbs/42nyADFsXag/s160-c/The%252520Fisherman.jpg",?? ????????????"https://lh4.googleusercontent.com/-iLyZlzfdy7s/URqvG0YScdI/AAAAAAAAAbs/1J9eDKmkXtk/s160-c/The%252520Night%252520is%252520Coming.jpg",?? ????????????"https://lh6.googleusercontent.com/-G-k7YkkUco0/URqvHhah6fI/AAAAAAAAAbs/_taQQG7t0vo/s160-c/The%252520Road.jpg",?? ????????????"https://lh6.googleusercontent.com/-h-ALJt7kSus/URqvIThqYfI/AAAAAAAAAbs/ejiv35olWS8/s160-c/Tokyo%252520Heights.jpg",?? ????????????"https://lh5.googleusercontent.com/-Hy9k-TbS7xg/URqvIjQMOxI/AAAAAAAAAbs/RSpmmOATSkg/s160-c/Tokyo%252520Highway.jpg",?? ????????????"https://lh6.googleusercontent.com/-83oOvMb4OZs/URqvJL0T7lI/AAAAAAAAAbs/c5TECZ6RONM/s160-c/Tokyo%252520Smog.jpg",?? ????????????"https://lh3.googleusercontent.com/-FB-jfgREEfI/URqvJI3EXAI/AAAAAAAAAbs/XfyweiRF4v8/s160-c/Tufa%252520at%252520Night.jpg",?? ????????????"https://lh4.googleusercontent.com/-vngKD5Z1U8w/URqvJUCEgPI/AAAAAAAAAbs/ulxCMVcU6EU/s160-c/Valley%252520Sunset.jpg",?? ????????????"https://lh6.googleusercontent.com/-DOz5I2E2oMQ/URqvKMND1kI/AAAAAAAAAbs/Iqf0IsInleo/s160-c/Windmill%252520Sunrise.jpg",?? ????????????"https://lh5.googleusercontent.com/-biyiyWcJ9MU/URqvKculiAI/AAAAAAAAAbs/jyPsCplJOpE/s160-c/Windmill.jpg",?? ????????????"https://lh4.googleusercontent.com/-PDT167_xRdA/URqvK36mLcI/AAAAAAAAAbs/oi2ik9QseMI/s160-c/Windmills.jpg",?? ????????????"https://lh5.googleusercontent.com/-kI_QdYx7VlU/URqvLXCB6gI/AAAAAAAAAbs/N31vlZ6u89o/s160-c/Yet%252520Another%252520Rockaway%252520Sunset.jpg",?? ????????????"https://lh4.googleusercontent.com/-e9NHZ5k5MSs/URqvMIBZjtI/AAAAAAAAAbs/1fV810rDNfQ/s160-c/Yosemite%252520Tree.jpg",?};?? }?? 圖片源已經(jīng)有了，現(xiàn)在我們就該考慮在哪里放置這些圖片了。新建或打開(kāi)activity_main.xml作為程序的主布局，加入如下代碼：
[html]?view plaincopy
<LinearLayout?xmlns:android="http://schemas.android.com/apk/res/android"??????xmlns:tools="http://schemas.android.com/tools"?? ????android:layout_width="wrap_content"?? ????android:layout_height="wrap_content"?>?? ??????????<GridView??? ????????android:id="@+id/photo_wall"?? ????????android:layout_width="match_parent"?? ????????android:layout_height="wrap_content"?? ????????android:columnWidth="90dip"?? ????????android:stretchMode="columnWidth"?? ????????android:numColumns="auto_fit"?? ????????android:verticalSpacing="10dip"?? ????????android:gravity="center"?? ????????></GridView>?? ??????</LinearLayout>?? 可以看到，我們?cè)谶@個(gè)布局文件中僅加入了一個(gè)GridView，這也就是我們程序中的“墻”，所有的圖片都將貼在這個(gè)“墻”上。
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接著我們定義GridView中每一個(gè)子View的布局，新建一個(gè)photo_layout.xml布局，加入如下代碼：
[html]?view plaincopy
<RelativeLayout?xmlns:android="http://schemas.android.com/apk/res/android"??????xmlns:tools="http://schemas.android.com/tools"?? ????android:layout_width="wrap_content"?? ????android:layout_height="wrap_content"?>?? ??????<ImageView??? ????????android:id="@+id/photo"?? ????????android:layout_width="90dip"?? ????????android:layout_height="90dip"?? ????????android:src="@drawable/empty_photo"?? ????????android:layout_centerInParent="true"?? ????????/>?? ??</RelativeLayout>?? 在每一個(gè)子View中我們就簡(jiǎn)單使用了一個(gè)ImageView來(lái)顯示一張圖片。這樣所有的布局就已經(jīng)定義好了。
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接下來(lái)新建PhotoWallAdapter做為GridView的適配器，代碼如下所示：
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public?class?PhotoWallAdapter?extends?ArrayAdapter<String>?implements?OnScrollListener?{???????? ????private?Set<BitmapWorkerTask>?taskCollection;?? ?????? ????private?LruCache<String,?Bitmap>?mMemoryCache;?? ?????? ????private?GridView?mPhotoWall;?? ?????? ????private?int?mFirstVisibleItem;?? ?????? ????private?int?mVisibleItemCount;?? ?????? ????private?boolean?isFirstEnter?=?true;?? ??????public?PhotoWallAdapter(Context?context,?int?textViewResourceId,?String[]?objects,?? ????????????GridView?photoWall)?{??????????super(context,?textViewResourceId,?objects);?? ????????mPhotoWall?=?photoWall;??????????taskCollection?=?new?HashSet<BitmapWorkerTask>();?? ???????? ????????int?maxMemory?=?(int)?Runtime.getRuntime().maxMemory();?? ????????int?cacheSize?=?maxMemory?/?8;?? ???????? ????????mMemoryCache?=?new?LruCache<String,?Bitmap>(cacheSize)?{?? ????????????@Override?? ????????????protected?int?sizeOf(String?key,?Bitmap?bitmap)?{?? ????????????????return?bitmap.getByteCount();?? ????????????}??????????};??????????mPhotoWall.setOnScrollListener(this);?? ????}????????@Override?? ????public?View?getView(int?position,?View?convertView,?ViewGroup?parent)?{?? ????????final?String?url?=?getItem(position);?? ????????View?view;??????????if?(convertView?==?null)?{?? ????????????view?=?LayoutInflater.from(getContext()).inflate(R.layout.photo_layout,?null);?? ????????}?else?{?? ????????????view?=?convertView;??????????}??????????final?ImageView?photo?=?(ImageView)?view.findViewById(R.id.photo);?? ???????? ????????photo.setTag(url);??????????setImageView(url,?photo);??????????return?view;?? ????}???????? ????private?void?setImageView(String?imageUrl,?ImageView?imageView)?{?? ????????Bitmap?bitmap?=?getBitmapFromMemoryCache(imageUrl);??????????if?(bitmap?!=?null)?{?? ????????????imageView.setImageBitmap(bitmap);??????????}?else?{?? ????????????imageView.setImageResource(R.drawable.empty_photo);??????????}??????}???????? ????public?void?addBitmapToMemoryCache(String?key,?Bitmap?bitmap)?{?? ????????if?(getBitmapFromMemoryCache(key)?==?null)?{?? ????????????mMemoryCache.put(key,?bitmap);??????????}??????}???????? ????public?Bitmap?getBitmapFromMemoryCache(String?key)?{?? ????????return?mMemoryCache.get(key);?? ????}????????@Override?? ????public?void?onScrollStateChanged(AbsListView?view,?int?scrollState)?{?? ???????? ????????if?(scrollState?==?SCROLL_STATE_IDLE)?{?? ????????????loadBitmaps(mFirstVisibleItem,?mVisibleItemCount);??????????}?else?{?? ????????????cancelAllTasks();??????????}??????}????????@Override?? ????public?void?onScroll(AbsListView?view,?int?firstVisibleItem,?int?visibleItemCount,?? ????????????int?totalItemCount)?{?? ????????mFirstVisibleItem?=?firstVisibleItem;??????????mVisibleItemCount?=?visibleItemCount;?????????? ???????? ????????if?(isFirstEnter?&&?visibleItemCount?>?0)?{?? ????????????loadBitmaps(firstVisibleItem,?visibleItemCount);??????????????isFirstEnter?=?false;?? ????????}??????}???????? ????private?void?loadBitmaps(int?firstVisibleItem,?int?visibleItemCount)?{?? ????????try?{?? ????????????for?(int?i?=?firstVisibleItem;?i?<?firstVisibleItem?+?visibleItemCount;?i++)?{?? ????????????????String?imageUrl?=?Images.imageThumbUrls[i];??????????????????Bitmap?bitmap?=?getBitmapFromMemoryCache(imageUrl);??????????????????if?(bitmap?==?null)?{?? ????????????????????BitmapWorkerTask?task?=?new?BitmapWorkerTask();?? ????????????????????taskCollection.add(task);??????????????????????task.execute(imageUrl);??????????????????}?else?{?? ????????????????????ImageView?imageView?=?(ImageView)?mPhotoWall.findViewWithTag(imageUrl);??????????????????????if?(imageView?!=?null?&&?bitmap?!=?null)?{?? ????????????????????????imageView.setImageBitmap(bitmap);??????????????????????}??????????????????}??????????????}??????????}?catch?(Exception?e)?{?? ????????????e.printStackTrace();??????????}??????}???????? ????public?void?cancelAllTasks()?{?? ????????if?(taskCollection?!=?null)?{?? ????????????for?(BitmapWorkerTask?task?:?taskCollection)?{?? ????????????????task.cancel(false);?? ????????????}??????????}??????}???????? ????class?BitmapWorkerTask?extends?AsyncTask<String,?Void,?Bitmap>?{?? ?????????? ????????private?String?imageUrl;?? ??????????@Override?? ????????protected?Bitmap?doInBackground(String...?params)?{?? ????????????imageUrl?=?params[0];?? ???????????? ????????????Bitmap?bitmap?=?downloadBitmap(params[0]);?? ????????????if?(bitmap?!=?null)?{?? ???????????????? ????????????????addBitmapToMemoryCache(params[0],?bitmap);?? ????????????}??????????????return?bitmap;?? ????????}????????????@Override?? ????????protected?void?onPostExecute(Bitmap?bitmap)?{?? ????????????super.onPostExecute(bitmap);?? ???????????? ????????????ImageView?imageView?=?(ImageView)?mPhotoWall.findViewWithTag(imageUrl);??????????????if?(imageView?!=?null?&&?bitmap?!=?null)?{?? ????????????????imageView.setImageBitmap(bitmap);??????????????}??????????????taskCollection.remove(this);?? ????????}???????????? ????????private?Bitmap?downloadBitmap(String?imageUrl)?{?? ????????????Bitmap?bitmap?=?null;?? ????????????HttpURLConnection?con?=?null;?? ????????????try?{?? ????????????????URL?url?=?new?URL(imageUrl);?? ????????????????con?=?(HttpURLConnection)?url.openConnection();??????????????????con.setConnectTimeout(5?*?1000);?? ????????????????con.setReadTimeout(10?*?1000);?? ????????????????bitmap?=?BitmapFactory.decodeStream(con.getInputStream());??????????????}?catch?(Exception?e)?{?? ????????????????e.printStackTrace();??????????????}?finally?{?? ????????????????if?(con?!=?null)?{?? ????????????????????con.disconnect();??????????????????}??????????????}??????????????return?bitmap;?? ????????}????????}????}?? PhotoWallAdapter是整個(gè)照片墻程序中最關(guān)鍵的一個(gè)類了，這里我來(lái)重點(diǎn)給大家講解一下。首先在PhotoWallAdapter的構(gòu)造函數(shù)中，我們初始化了LruCache類，并設(shè)置了最大緩存容量為程序最大可用內(nèi)存的1/8，接下來(lái)又為GridView注冊(cè)了一個(gè)滾動(dòng)監(jiān)聽(tīng)器。然后在getView()方法中，我們?yōu)槊總€(gè)ImageView設(shè)置了一個(gè)唯一的Tag，這個(gè)Tag的作用是為了后面能夠準(zhǔn)確地找回這個(gè)ImageView，不然異步加載圖片會(huì)出現(xiàn)亂序的情況。之后調(diào)用了setImageView()方法為ImageView設(shè)置一張圖片，這個(gè)方法首先會(huì)從LruCache緩存中查找是否已經(jīng)緩存了這張圖片，如果成功找到則將緩存中的圖片顯示在ImageView上，否則就顯示一張默認(rèn)的空?qǐng)D片。
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看了半天，那到底是在哪里下載圖片的呢？這是在GridView的滾動(dòng)監(jiān)聽(tīng)器中進(jìn)行的，在onScrollStateChanged()方法中，我們對(duì)GridView的滾動(dòng)狀態(tài)進(jìn)行了判斷，如果當(dāng)前GridView是靜止的，則調(diào)用loadBitmaps()方法去下載圖片，如果GridView正在滾動(dòng)，則取消掉所有下載任務(wù)，這樣可以保證GridView滾動(dòng)的流暢性。在loadBitmaps()方法中，我們?yōu)槠聊簧纤锌梢?jiàn)的GridView子元素開(kāi)啟了一個(gè)線程去執(zhí)行下載任務(wù)，下載成功后將圖片存儲(chǔ)到LruCache當(dāng)中，然后通過(guò)Tag找到相應(yīng)的ImageView控件，把下載好的圖片顯示出來(lái)。
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由于我們使用了LruCache來(lái)緩存圖片，所以不需要擔(dān)心內(nèi)存溢出的情況，當(dāng)LruCache中存儲(chǔ)圖片的總大小達(dá)到容量上限的時(shí)候，會(huì)自動(dòng)把最近最少使用的圖片從緩存中移除。
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最后新建或打開(kāi)MainActivity作為程序的主Activity，代碼如下所示：
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public?class?MainActivity?extends?Activity?{???????? ????private?GridView?mPhotoWall;?? ?????? ????private?PhotoWallAdapter?adapter;?? ??????@Override?? ????protected?void?onCreate(Bundle?savedInstanceState)?{?? ????????super.onCreate(savedInstanceState);?? ????????setContentView(R.layout.activity_main);??????????mPhotoWall?=?(GridView)?findViewById(R.id.photo_wall);??????????adapter?=?new?PhotoWallAdapter(this,?0,?Images.imageThumbUrls,?mPhotoWall);?? ????????mPhotoWall.setAdapter(adapter);??????}????????@Override?? ????protected?void?onDestroy()?{?? ????????super.onDestroy();?? ???????? ????????adapter.cancelAllTasks();??????}????}?? MainActivity中的代碼非常簡(jiǎn)單，沒(méi)什么需要說(shuō)明的了，在Activity被銷毀時(shí)取消掉了所有的下載任務(wù)，避免程序在后臺(tái)耗費(fèi)流量。另外由于我們使用了網(wǎng)絡(luò)功能，別忘了在AndroidManifest.xml中加入網(wǎng)絡(luò)權(quán)限的聲明。
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現(xiàn)在可以運(yùn)行一下程序了，效果如下圖所示：
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可以看到，滾動(dòng)照片墻，會(huì)異步加載圖片到相應(yīng)的ImageView上。隨著加載圖片的增多，會(huì)釋放掉一些之前加載過(guò)的圖片，你多滾動(dòng)幾次就可以看得出了。另外為了能讓大家明顯看出圖片的釋放情況，我在這個(gè)程序中沒(méi)有使用本地緩存，所有被釋放掉的圖片再次顯示需要從網(wǎng)絡(luò)上再下載一遍。在實(shí)際的項(xiàng)目中配合適當(dāng)?shù)谋镜鼐彺嫘Ч麜?huì)更好。
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打開(kāi)DDMS，我們可以發(fā)現(xiàn)，由于有LruCache幫我們管理圖片緩存，不管如何滾動(dòng)照片墻，程序內(nèi)存始終會(huì)保持在一個(gè)合理的范圍內(nèi)。
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本篇文章的重點(diǎn)在于如何對(duì)圖片進(jìn)行更好的回收，因此照片墻只是簡(jiǎn)單地使用GridView進(jìn)行了展示，想要看更酷更炫的照片墻效果的朋友，可以參考我后面的一篇文章?Android瀑布流照片墻實(shí)現(xiàn)，體驗(yàn)不規(guī)則排列的美感?。
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好了，今天的講解到此結(jié)束，有疑問(wèn)的朋友請(qǐng)?jiān)谙旅媪粞浴?/p>
本文轉(zhuǎn)自農(nóng)夫山泉?jiǎng)e墅博客園博客，原文鏈接：http://www.cnblogs.com/yaowen/p/6347857.html，如需轉(zhuǎn)載請(qǐng)自行聯(lián)系原作者
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