淺談Android截屏和指定View生成截圖

/**
 * 截取當前窗體的截圖，根據[isShowStatusBar]判斷是否包含當前窗體的狀態欄
 * 原理是獲取當前窗體decorView的緩存生成圖片
 */
fun captureWindow(activity: Activity, isShowStatusBar: Boolean): Bitmap? {
    // 獲取當前窗體的View對象
    val view = activity.window.decorView
    view.isDrawingCacheEnabled = true
    // 生成緩存
    view.buildDrawingCache()

    val bitmap = if (isShowStatusBar) {
        // 繪制整個窗體，包括狀態欄
        Bitmap.createBitmap(view.drawingCache, 0, 0, view.measuredWidth, view.measuredHeight)
    } else {
        // 獲取狀態欄高度
        val rect = Rect()
        view.getWindowVisibleDisplayFrame(rect)
        val display = activity.windowManager.defaultDisplay

        // 減去狀態欄高度
        Bitmap.createBitmap(view.drawingCache, 0,
                rect.top, display.width, display.height - rect.top)
    }

    view.isDrawingCacheEnabled = false
    view.destroyDrawingCache()

    return bitmap
}

/**
  * View已經在界面上展示瞭，可以直接獲取View的緩存
  * 對View進行量測，佈局後生成View的緩存
  * View為固定大小的View，包括TextView,ImageView,LinearLayout,FrameLayout,RelativeLayout等
  * @param view 截取的View,View必須有固定的大小，不然drawingCache返回null
  * @return 生成的Bitmap
  */
fun captureView(view: View): Bitmap? {
        view.isDrawingCacheEnabled = true
        view.buildDrawingCache()
        // 重新測量一遍View的寬高
        view.measure(View.MeasureSpec.makeMeasureSpec(view.width, View.MeasureSpec.EXACTLY),
                View.MeasureSpec.makeMeasureSpec(view.height, View.MeasureSpec.EXACTLY))
        // 確定View的位置
        view.layout(view.x.toInt(), view.y.toInt(), view.x.toInt() + view.measuredWidth,
                view.y.toInt() + view.measuredHeight)
        // 生成View寬高一樣的Bitmap
        val bitmap = Bitmap.createBitmap(view.drawingCache, 0, 0, view.measuredWidth,
                view.measuredHeight)
        view.isDrawingCacheEnabled = false
        view.destroyDrawingCache()
        return bitmap
}

/**
 * 截取ScrollerView
 * 原理是獲取scrollView的子View的高度，然後創建一個子View寬高的畫佈，將ScrollView繪制在畫佈上
 * @param scrollView 控件
 * @return 返回截圖後的Bitmap
 */
fun captureScrollView(scrollView: ScrollView): Bitmap? {
     var h = 0
     for (i in 0 until scrollView.childCount) {
         val childView = scrollView.getChildAt(i)
         // 獲取子View的高度
         h += childView.height
         // 設置背景顏色，避免佈局裡未設置背景顏色，截的圖背景黑色
         childView.setBackgroundColor(Color.parseColor("#FFFFFF"))
     }

     val bitmap = createBitmap(scrollView.width, h)
     val canvas = Canvas(bitmap)
     // 將ScrollView繪制在畫佈上
     scrollView.draw(canvas)
     return bitmap
}

/**
 * 截取ListView
 * 原理：獲取到每一個子View，將子View生成的bitmap存入集合，並且累積ListView高度
 * 遍歷完成後，創建一個ListView大小的畫佈，將集合的Bitmap繪制到畫佈上
 * @param listView 截圖控件對象
 * @return 生成的截圖對象
 */
fun captureListView(listView: ListView): Bitmap? {
        val adapter = listView.adapter
        val itemCount = adapter.count
        var allitemsheight = 0
        val bitmaps = ArrayList<Bitmap>()

        for (i in 0 until itemCount) {
            // 獲取每一個子View
            val childView = adapter.getView(i, null, listView)
            // 測量寬高
            childView.measure(
                    View.MeasureSpec.makeMeasureSpec(listView.width, View.MeasureSpec.EXACTLY),
                    View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED))

            // 佈局位置
            childView.layout(0, 0, childView.measuredWidth, childView.measuredHeight)
            // 設置背景顏色，避免是黑色的
            childView.setBackgroundColor(Color.parseColor("#FFFFFF"))
            childView.isDrawingCacheEnabled = true
            // 生成緩存
            childView.buildDrawingCache()
            // 將每一個View的截圖加入集合
            bitmaps.add(childView.drawingCache)
            // 疊加截圖高度
            allitemsheight += childView.measuredHeight
        }

        // 創建和ListView寬高一樣的畫佈
        val bitmap = createBitmap(listView.measuredWidth, allitemsheight)
        val canvas = Canvas(bitmap)

        val paint = Paint()
        var iHeight = 0f

        for (i in bitmaps.indices) {
            val bmp: Bitmap = bitmaps[i]
            // 將每一個生成的bitmap繪制在畫佈上
            canvas.drawBitmap(bmp, 0f, iHeight, paint)
            iHeight += bmp.height

            bmp.recycle()
        }
        return bitmap
}

/**
 * 截取RecyclerView
 * 原理和ListView集合是一樣的，獲取到每一個Holder的截圖放入集合，最後統一繪制到Bitmap上
 * @param recyclerView 要截圖的控件
 * @return 生成的截圖
 */
fun captureRecyclerView(recyclerView: RecyclerView): Bitmap? {
        val adapter = recyclerView.adapter
        var bigBitmap: Bitmap? = null
        if (adapter != null) {
            val size = adapter.itemCount
            var height = 0
            val paint = Paint()
            var iHeight = 0
            val maxMemory = (Runtime.getRuntime().maxMemory() / 1024).toInt()

            // Use 1/8th of the available memory for this memory cache.
            val cacheSize = maxMemory / 8
            val bitmapCache = LruCache<String, Bitmap>(cacheSize)
            for (i in 0 until size) {
                val holder = adapter.createViewHolder(recyclerView, adapter.getItemViewType(i))
                adapter.onBindViewHolder(holder, i)
                holder.itemView.measure(
                        View.MeasureSpec.makeMeasureSpec(recyclerView.width, View.MeasureSpec.EXACTLY),
                        View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED))
                holder.itemView.layout(0, 0, holder.itemView.measuredWidth,
                        holder.itemView.measuredHeight)
                holder.itemView.setBackgroundColor(Color.parseColor("#FFFFFF"))
                holder.itemView.isDrawingCacheEnabled = true
                holder.itemView.buildDrawingCache()
                val drawingCache = holder.itemView.drawingCache
                if (drawingCache != null) {
                    bitmapCache.put(i.toString(), drawingCache)
                }
                height += holder.itemView.measuredHeight
            }

            bigBitmap = createBitmap(recyclerView.measuredWidth, height)
            val bigCanvas = Canvas(bigBitmap!!)
            val lBackground = recyclerView.background
            if (lBackground is ColorDrawable) {
                val lColor = lBackground.color
                bigCanvas.drawColor(lColor)
            }

            for (i in 0 until size) {
                val bitmap = bitmapCache.get(i.toString())
                bigCanvas.drawBitmap(bitmap, 0f, iHeight.toFloat(), paint)
                iHeight += bitmap.height
                bitmap.recycle()
            }
        }
        return bigBitmap
}

/**
 * 截取WebView，包含WebView的整個長度
 * 在WebView渲染之前要加上以下代碼，開啟Html緩存，不然會截屏空白
 *  if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
 *      WebView.enableSlowWholeDocumentDraw()
 *  }
 *  WebView的截圖很容易遇到內存溢出的問題，因為WebView可以加載很多內容，導致生成的圖片特別長，創建Bitmap時容易OOM
 */
fun captureWebView(webView: WebView): Bitmap? {
        // 重新調用WebView的measure方法測量實際View的大小（將測量模式設置為UNSPECIFIED模式也就是需要多大就可以獲得多大的空間）
        webView.measure(View.MeasureSpec.makeMeasureSpec(View.MeasureSpec.UNSPECIFIED, View.MeasureSpec.UNSPECIFIED),
                View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED))
        // 調用layout方法設置佈局（使用新測量的大小）
        webView.layout(0, 0, webView.measuredWidth, webView.measuredHeight)
        // 開啟WebView的緩存(當開啟這個開關後下次調用getDrawingCache()方法的時候會把view繪制到一個bitmap上)
        webView.isDrawingCacheEnabled = true
        // 強制繪制緩存（必須在setDrawingCacheEnabled(true)之後才能調用，否者需要手動調用destroyDrawingCache()清楚緩存）
        webView.buildDrawingCache()

        val bitmap = createBitmap(webView.measuredWidth, webView.measuredHeight)

        // 已picture為背景創建一個畫佈
        val canvas = Canvas(bitmap)  // 畫佈的寬高和 WebView 的網頁保持一致
        val paint = Paint()
        // 設置畫筆的定點位置，也就是左上角
        canvas.drawBitmap(bitmap, 0f, webView.measuredHeight * 1f, paint)
        // 將WebView繪制在剛才創建的畫板上
        webView.draw(canvas)
        webView.isDrawingCacheEnabled = false
        webView.destroyDrawingCache()
        return bitmap
}