Android Bitmap内存管理与OOM治理从崩溃现场到可控降级策略

java.lang.OutOfMemoryError: Failed to allocate a 16777228 byte allocation with 4194304 free bytes and 3MB until OOM
    at android.graphics.BitmapFactory.nativeDecodeStream(Native Method)
    at android.graphics.BitmapFactory.decodeStream(BitmapFactory.java:700)

内存占用 = 宽度 × 高度 × 单像素字节数

1920 × 1080 × 4 = 8,294,400 字节 ≈ 8 MB

fun decodeSampledBitmap(filePath: String, reqWidth: Int, reqHeight: Int): Bitmap? {
    val options = BitmapFactory.Options().apply {
        inJustDecodeBounds = true  // 仅解析尺寸，不加载像素数据
    }
    BitmapFactory.decodeFile(filePath, options)

    // 计算采样率
    options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight)
    options.inJustDecodeBounds = false
    return BitmapFactory.decodeFile(filePath, options)
}

fun calculateInSampleSize(options: BitmapFactory.Options, reqWidth: Int, reqHeight: Int): Int {
    val (width, height) = options.outWidth to options.outHeight
    var inSampleSize = 1

    if (height > reqHeight || width > reqWidth) {
        val halfHeight = height / 2
        val halfWidth = width / 2

        // 计算最大的 inSampleSize 值（2 的幂次），保证宽高都大于目标尺寸
        while (halfHeight / inSampleSize >= reqHeight && halfWidth / inSampleSize >= reqWidth) {
            inSampleSize *= 2
        }
    }
    return inSampleSize
}

val options = BitmapFactory.Options().apply {
    inPreferredConfig = Bitmap.Config.RGB_565
}
val bitmap = BitmapFactory.decodeFile(filePath, options)

class BitmapPool {
    private val pool = mutableSetOf<Bitmap>()

    fun getBitmap(width: Int, height: Int, config: Bitmap.Config): Bitmap {
        synchronized(pool) {
            val reusable = pool.find { 
                it.width == width && it.height == height && it.config == config 
            }
            return if (reusable != null) {
                pool.remove(reusable)
                reusable
            } else {
                Bitmap.createBitmap(width, height, config)
            }
        }
    }

    fun put(bitmap: Bitmap) {
        synchronized(pool) {
            if (pool.size < MAX_POOL_SIZE) {
                pool.add(bitmap)
            } else {
                bitmap.recycle()  // Android 8.0 以下需要手动释放
            }
        }
    }

    companion object {
        private const val MAX_POOL_SIZE = 10
    }
}

val options = BitmapFactory.Options().apply {
    inMutable = true
    inBitmap = bitmapPool.getBitmap(targetWidth, targetHeight, Bitmap.Config.ARGB_8888)
}
val bitmap = BitmapFactory.decodeFile(filePath, options)

Glide.with(context)
    .load(imageUrl)
    .override(targetWidth, targetHeight)  // 自动计算采样率
    .format(DecodeFormat.PREFER_RGB_565)  // 降级为 RGB_565
    .diskCacheStrategy(DiskCacheStrategy.AUTOMATIC)
    .into(imageView)

class MyApplication : Application() {
    override fun onCreate() {
        super.onCreate()
        val activityManager = getSystemService(Context.ACTIVITY_SERVICE) as ActivityManager
        val memoryClass = activityManager.memoryClass  // 每个应用的最大堆内存（MB）

        if (memoryClass <= 128) {  // 低内存设备
            Glide.get(this).setMemoryCategory(MemoryCategory.LOW)
        }
    }

    override fun onTrimMemory(level: Int) {
        super.onTrimMemory(level)
        when (level) {
            ComponentCallbacks2.TRIM_MEMORY_UI_HIDDEN -> {
                // 应用进入后台，清理内存缓存
                Glide.get(this).clearMemory()
            }
            ComponentCallbacks2.TRIM_MEMORY_RUNNING_CRITICAL -> {
                // 系统内存极度紧张，清理全部缓存
                Glide.get(this).clearMemory()
            }
        }
    }
}

// 检测大 Bitmap 泄漏
dependencies {
    debugImplementation 'com.squareup.leakcanary:leakcanary-android:2.12'
}

fun loadImageSafely(context: Context, url: String, imageView: ImageView) {
    try {
        Glide.with(context)
            .load(url)
            .error(R.drawable.placeholder)  // 加载失败时显示占位图
            .into(imageView)
    } catch (e: OutOfMemoryError) {
        // OOM 发生时的兜底逻辑
        imageView.setImageResource(R.drawable.placeholder)
        logOOMEvent(e)
        System.gc()  // 尝试触发 GC（不保证立即执行）
    }
}

fun logOOMEvent(e: OutOfMemoryError) {
    val runtime = Runtime.getRuntime()
    val usedMemory = (runtime.totalMemory() - runtime.freeMemory()) / 1024 / 1024
    val maxMemory = runtime.maxMemory() / 1024 / 1024
    Log.e("OOM", "Used: ${usedMemory}MB, Max: ${maxMemory}MB", e)
    // 上报到崩溃平台（如 Firebase Crashlytics）
}

recyclerView.layoutManager = LinearLayoutManager(context).apply {
    // 禁用 RecyclerView 的预取（Prefetch）机制
    isItemPrefetchEnabled = false
}

// 或者使用 Glide 的预加载控制
val preloadSizeProvider = ViewPreloadSizeProvider<String>()
val preloader = RecyclerViewPreloader(
    Glide.with(this),
    modelProvider,
    preloadSizeProvider,
    3  // 限制预加载数量为 3 个
)
recyclerView.addOnScrollListener(preloader)