The correct way to take screenshots of Android Views

Mar 4, 2022142

AI Translation

This post is translated from Chinese into English through AI.View Original

AI-generated summary

This article discusses different methods for taking screenshots of Android views. The methods include enabling drawing cache, creating a bitmap and drawing the view onto it, and using the view's drawing cache. It also mentions a potential issue where the screenshot may not reflect the updated view, and suggests refreshing the drawing cache or disabling the drawing cache after use.

Screenshots#

Method 1:


//Method 1
    fun takePic(view: View, width: Float, height: Float, scroll: Boolean, config: Bitmap.Config?): Bitmap? {
        var width = width
        var height = height
        if (!view.isDrawingCacheEnabled) {
            //isDrawingCacheEnabled is deprecated
            view.isDrawingCacheEnabled = true
        }
        if (width == 0f) {
            width = Consts.width
        }
        if (height == 0f) {
            height = Consts.height
        }
        val bitmap = Bitmap.createBitmap(width.toInt(), height.toInt(), config!!)
        bitmap.eraseColor(Color.WHITE)
        val canvas = Canvas(bitmap)
        var left = view.left
        var top = view.top
        if (scroll) {
            left = view.scrollX
            top = view.scrollY
        }
        val status: Int = canvas.save()
        canvas.translate(-left, -top)
        val scale = width / view.width
        canvas.scale(scale, scale, left, top)
        view.draw(canvas)
        canvas.restoreToCount(status)
        val alphaPaint = Paint()
        alphaPaint.setColor(Color.TRANSPARENT)
        canvas.drawRect(0f, 0f, 1f, height, alphaPaint)
        canvas.drawRect(width - 1f, 0f, width, height, alphaPaint)
        canvas.drawRect(0f, 0f, width, 1f, alphaPaint)
        canvas.drawRect(0f, height - 1f, width, height, alphaPaint)
        canvas.setBitmap(null)
        return bitmap
    }

//Method 2
    fun takePic(v: View, width: Int, height: Int, config: Bitmap.Config?): Bitmap? {
        val bmp = Bitmap.createBitmap(v.width, v.height, config!!)
        val c = Canvas(bmp)
        c.drawColor(Color.WHITE)
        v.draw(c)
        return bmp
    }

//Method 3: I think this is the simplest and most useful method, but there is a big pit here, which I will explain later
    fun takePic(view: View): Bitmap? {
        view.buildDrawingCache()
        return view.drawingCache
    }

//Method 4
    fun takePic(v: View): Bitmap? {
        val bmp = Bitmap.createBitmap(v.width, v.height, Bitmap.Config.ARGB_8888)
        val c = Canvas(bmp)
        c.drawColor(Color.WHITE)
        v.draw(c)
        return bmp
    }

Issue#

The above are all methods for capturing screenshots of views. However, sometimes there is a situation where the screenshot remains the same even after the view has changed. In this case, you need to refresh the view's drawing cache. For example, the big pit mentioned in Method 3 is that you need to call view.destroyDrawingCache() before the next call. Or if you have called the setDrawingCacheEnabled(true) method, you need to call setDrawingCacheEnabled(false) after you finish using it.

//Method 1 fun takePic(view: View, width: Float, height: Float, scroll: Boolean, config: Bitmap.Config?): Bitmap? { var width = width var height = height if (!view.isDrawingCacheEnabled) { //isDrawingCacheEnabled is deprecated view.isDrawingCacheEnabled = true } if (width == 0f) { width = Consts.width } if (height == 0f) { height = Consts.height } val bitmap = Bitmap.createBitmap(width.toInt(), height.toInt(), config!!) bitmap.eraseColor(Color.WHITE) val canvas = Canvas(bitmap) var left = view.left var top = view.top if (scroll) { left = view.scrollX top = view.scrollY } val status: Int = canvas.save() canvas.translate(-left, -top) val scale = width / view.width canvas.scale(scale, scale, left, top) view.draw(canvas) canvas.restoreToCount(status) val alphaPaint = Paint() alphaPaint.setColor(Color.TRANSPARENT) canvas.drawRect(0f, 0f, 1f, height, alphaPaint) canvas.drawRect(width - 1f, 0f, width, height, alphaPaint) canvas.drawRect(0f, 0f, width, 1f, alphaPaint) canvas.drawRect(0f, height - 1f, width, height, alphaPaint) canvas.setBitmap(null) return bitmap } //Method 2 fun takePic(v: View, width: Int, height: Int, config: Bitmap.Config?): Bitmap? { val bmp = Bitmap.createBitmap(v.width, v.height, config!!) val c = Canvas(bmp) c.drawColor(Color.WHITE) v.draw(c) return bmp } //Method 3: I think this is the simplest and most useful method, but there is a big pit here, which I will explain later fun takePic(view: View): Bitmap? { view.buildDrawingCache() return view.drawingCache } //Method 4 fun takePic(v: View): Bitmap? { val bmp = Bitmap.createBitmap(v.width, v.height, Bitmap.Config.ARGB_8888) val c = Canvas(bmp) c.drawColor(Color.WHITE) v.draw(c) return bmp }