Android Gldie复用只取之前decode过的缓存resource，Kotlin

import android.graphics.Bitmap
import android.os.Bundle
import android.util.Log
import android.widget.ImageView
import androidx.appcompat.app.AppCompatActivity
import androidx.lifecycle.lifecycleScope
import com.bumptech.glide.load.DataSource
import com.bumptech.glide.load.engine.GlideException
import com.bumptech.glide.load.resource.bitmap.CenterCrop
import com.bumptech.glide.request.RequestListener
import com.bumptech.glide.request.target.Target
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.channels.Channel
import kotlinx.coroutines.flow.receiveAsFlow
import kotlinx.coroutines.launchclass MainActivity : AppCompatActivity() {private val TAG = "Glide/${this::class.simpleName}"companion object {const val FAIL = -1const val SUCCESS = 1const val SIZE = 400}private val mCrop = CenterCrop()private val resId = R.mipmap.pic2private var mImageView: ImageView? = nullprivate val mChannel = Channel<Int>()override fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)setContentView(R.layout.activity_main)val imageView = findViewById<ImageView>(R.id.image)mImageView = findViewById(R.id.image2)GlideApp.with(this).asBitmap().load(resId).transform(mCrop).override(SIZE, SIZE).addListener(object : RequestListener<Bitmap> {override fun onl oadFailed(e: GlideException?,model: Any?,target: Target<Bitmap>,isFirstResource: Boolean): Boolean {Log.d(TAG, "onLoadFailed")signal(FAIL)return false}override fun onResourceReady(resource: Bitmap,model: Any,target: Target<Bitmap>?,dataSource: DataSource,isFirstResource: Boolean): Boolean {Log.d(TAG, "onResourceReady")signal(SUCCESS)return false}}).into(imageView)waitReceive()}fun signal(s: Int) {lifecycleScope.launch(Dispatchers.IO) {mChannel.send(s)}}private fun waitReceive() {lifecycleScope.launch(Dispatchers.IO) {mChannel.receiveAsFlow().collect {Log.d(TAG, "collect $it")if (it == SUCCESS) {fetchCacheBitmap()}}}}private fun fetchCacheBitmap() {val bitmap = runCatching {GlideApp.with(this@MainActivity).asBitmap().load(resId).transform(mCrop).onlyRetrieveFromCache(true) //从内存或者glide decode好的resource里面取，不去原始decode.override(SIZE, SIZE).addListener(object : RequestListener<Bitmap> {override fun onl oadFailed(e: GlideException?,model: Any?,target: Target<Bitmap>,isFirstResource: Boolean): Boolean {Log.d(TAG, "cache onl oadFailed")return false}override fun onResourceReady(resource: Bitmap,model: Any,target: Target<Bitmap>?,dataSource: DataSource,isFirstResource: Boolean): Boolean {Log.d(TAG, "cache onResourceReady")return false}}).submit().get() //不要在这里加timeout值}.onFailure {Log.d(TAG, "取Glide缓存失败:${it.message}")}.onSuccess {Log.d(TAG, "取Glide缓存成功:${it.byteCount}")}.getOrNull()Log.d(TAG, "getOrNull=${bitmap?.byteCount}")if (bitmap != null) {lifecycleScope.launch(Dispatchers.Main) {//之前的缓存资源取到了。//使用之前的缓存，设置到新的ImageView里面。mImageView?.setImageBitmap(bitmap)}}}
}

可以看到，第一次因为是全新的加载，没有缓存，glide只能干脏活，把原始的图片文件decode成resource，花费200+毫秒，而之后，只从缓存（包括磁盘的resource半成品）中取，仅仅花费20+毫秒，时间开销是原先的约1/10，加载速度相当于快了约10倍。

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