Getdrawingcache of view is empty. Solution: interview questions for Android audio and video development

final boolean use32BitCache = attachInfo != null && attachInfo.mUse32BitDrawingCache;

if (width <= 0 || height <= 0 ||

// Projected bitmap size in bytes

(width * height * (opaque && !use32BitCache ? 2 : 4) >

ViewConfiguration.get(mContext).getScaledMaximumDrawingCacheSize())) {

destroyDrawingCache();

mCachingFailed = true;

return;

}

boolean clear = true;

Bitmap bitmap = autoScale ? mDrawingCache : mUnscaledDrawingCache;

if (bitmap == null || bitmap.getWidth() != width || bitmap.getHeight() != height) {

Bitmap.Config quality;

if (!opaque) {

// Never pick ARGB_4444 because it looks awful

// Keep the DRAWING_CACHE_QUALITY_LOW flag just in case

switch (mViewFlags & DRAWING_CACHE_QUALITY_MASK) {

case DRAWING_CACHE_QUALITY_AUTO:

quality = Bitmap.Config.ARGB_8888;

break;

case DRAWING_CACHE_QUALITY_LOW:

quality = Bitmap.Config.ARGB_8888;

break;

case DRAWING_CACHE_QUALITY_HIGH:

quality = Bitmap.Config.ARGB_8888;

break;

default:

quality = Bitmap.Config.ARGB_8888;

break;

}

} else {

// Optimization for translucent windows

// If the window is translucent, use a 32 bits bitmap to benefit from memcpy()

quality = use32BitCache ? Bitmap.Config.ARGB_8888 : Bitmap.Config.RGB_565;

}

// Try to cleanup memory

if (bitmap != null) bitmap.recycle();

try {

bitmap = Bitmap.createBitmap(width, height, quality);

bitmap.setDensity(getResources().getDisplayMetrics().densityDpi);

if (autoScale) {

mDrawingCache = bitmap;

} else {

mUnscaledDrawingCache = bitmap;

}

if (opaque && use32BitCache) bitmap.setHasAlpha(false);

} catch (OutOfMemoryError e) {

// If there is not enough memory to create the bitmap cache, just

// ignore the issue as bitmap caches are not required to draw the

// view hierarchy

if (autoScale) {

mDrawingCache = null;

} else {

mUnscaledDrawingCache = null;

}

mCachingFailed = true;

return;

}

clear = drawingCacheBackgroundColor != 0;

}

Canvas canvas;

if (attachInfo != null) {

canvas = attachInfo.mCanvas;

if (canvas == null) {

canvas = new Canvas();

}

canvas.setBitmap(bitmap);

// Temporarily clobber the cached Canvas in case one of our children

// is also using a drawing cache. Without this, the children would

// steal the canvas by attaching their own bitmap to it and bad, bad

// thing would happen (invisible views, corrupted drawings, etc.)

attachInfo.mCanvas = null;

} else {

// This case should hopefully never or seldom happen

canvas = new Canvas(bitmap);

}

if (clear) {

bitmap.eraseColor(drawingCacheBackgroundColor);

}

computeScroll();

final int restoreCount = canvas.save();

if (autoScale && scalingRequired) {

final float scale = attachInfo.mApplicationScale;

canvas.scale(scale, scale);

}

canvas.translate(-mScrollX, -mScrollY);

mPrivateFlags |= DRAWN;

if (mAttachInfo == null || !mAttachInfo.mHardwareAccelerated ||

mLayerType != LAYER_TYPE_NONE) {

mPrivateFlags |= DRAWING_CACHE_VALID;

}

// Fast path for layouts with no backgrounds

if ((mPrivateFlags & SKIP_DRAW) == SKIP_DRAW) {

if (ViewDebug.TRACE_HIERARCHY) {

ViewDebug.trace(this, ViewDebug.HierarchyTraceType.DRAW);

}

mPrivateFlags &= ~DIRTY_MASK;

dispatchDraw(canvas);

} else {

draw(canvas);

}

canvas.restoreToCount(restoreCount);

canvas.setBitmap(null);

if (attachInfo != null) {

// Restore the cached Canvas for our siblings

attachInfo.mCanvas = canvas;

}

}

}

/**

• Create a snapshot of the view into a bitmap. We should probably make

• some form of this public, but should think about the API.

*/

Bitmap createSnapshot(Bitmap.Config quality, int backgroundColor, boolean skipChildren) {

int width = mRight - mLeft;

int height = mBottom - mTop;

final AttachInfo attachInfo = mAttachInfo;

final float scale = attachInfo != null ? attachInfo.mApplicationScale : 1.0f;

width = (int) ((width * scale) + 0.5f);

height = (int) ((height * scale) + 0.5f);

Bitmap bitmap = Bitmap.createBitmap(width > 0 ? width : 1, height > 0 ? height : 1, quality);

if (bitmap == null) {

throw new OutOfMemoryError();

}

Resources resources = getResources();

if (resources != null) {

bitmap.setDensity(resources.getDisplayMetrics().densityDpi);

}

Canvas canvas;

if (attachInfo != null) {

canvas = attachInfo.mCanvas;

if (canvas == null) {

canvas = new Canvas();

}

canvas.setBitmap(bitmap);

// Temporarily clobber the cached Canvas in case one of our children

// is also using a drawing cache. Without this, the children would

// steal the canvas by attaching their own bitmap to it and bad, bad

// things would happen (invisible views, corrupted drawings, etc.)

attachInfo.mCanvas = null;

} else {

// This case should hopefully never or seldom happen

canvas = new Canvas(bitmap);

}

if ((backgroundColor & 0xff000000) != 0) {

bitmap.eraseColor(backgroundColor);

}

computeScroll();

final int restoreCount = canvas.save();

canvas.scale(scale, scale);

canvas.translate(-mScrollX, -mScrollY);

// Temporarily remove the dirty mask

int flags = mPrivateFlags;

mPrivateFlags &= ~DIRTY_MASK;

// Fast path for layouts with no backgrounds

if ((mPrivateFlags & SKIP_DRAW) == SKIP_DRAW) {

dispatchDraw(canvas);

} else {

draw(canvas);

}

Learning sharing

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Many friends are not without information , Most of them are dozens or hundreds G, But it's messy , I don't know how to look, where to start , Even after reading, I forget

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First of all , Learning knowledge is fragmented , There is no reasonable learning route and advanced direction .
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2%E4%BD%95%E9%9D%A2%E8%AF%95%E6%8B%BF%E9%AB%98%E8%96%AA%EF%BC%81.md)

[ Outside the chain picture transfer in …(img-yLxbCVLN-1645006346132)]

Seven modules of learning materials ： Such as NDK Module development 、Android Framework architecture …

[ Outside the chain picture transfer in …(img-G3Su729S-1645006346133)]

Only the system , Learning with direction , In order to quickly improve their own technology in a period of time .

This system learning notes , Adapt to the crowd ：
First of all , Learning knowledge is fragmented , There is no reasonable learning route and advanced direction .
second , Several years of development , I don't know how to advance further , More confused .
Third , At the right age , The follow-up doesn't know how to develop , Transformation Management , Or strengthen technical research . If you need it , I have exactly why , Don't come to collect ！ Maybe it can change your current state ！
Because of the more content of the article , Space is not allowed , Some of the contents not shown are shown in the form of screenshots . If you need to get a complete document, please click my GitHub Free access .