Android截屏的原理：获取具体需要截屏的区域的Bitmap，然后绘制在画布上，保存为图片后进行分享或者其它用途
在截屏功能中，有时需要截取全屏的内容，有时需要截取超过一屏的内容（比如：Listview，Scrollview，RecyclerView）。下面介绍各种场景获取Bitmap的方法
普通截屏的实现
获取当前Window的DrawingCache的方式，即decorView的DrawingCache
public static Bitmap shotActivity(Activity ctx) {
View view = ctx.getWindow().getDecorView();
view.setDrawingCacheEnabled(true);
view.buildDrawingCache();
Bitmap bp = Bitmap.createBitmap(view.getDrawingCache(), 0, 0, view.getMeasuredWidth(),
view.getMeasuredHeight());
view.setDrawingCacheEnabled(false);
view.destroyDrawingCache();
return bp;
}
获取当前View的DrawingCache
public static Bitmap getViewBp(View v) {
if (null == v) {
return null;
}
v.setDrawingCacheEnabled(true);
v.buildDrawingCache();
if (Build.VERSION.SDK_INT >= 11) {
v.measure(MeasureSpec.makeMeasureSpec(v.getWidth(),
MeasureSpec.EXACTLY), MeasureSpec.makeMeasureSpec(
v.getHeight(), MeasureSpec.EXACTLY));
v.layout((int) v.getX(), (int) v.getY(),
(int) v.getX() + v.getMeasuredWidth(),
(int) v.getY() + v.getMeasuredHeight());
} else {
v.measure(MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED),
MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED));
v.layout(0, 0, v.getMeasuredWidth(), v.getMeasuredHeight());
}
Bitmap b = Bitmap.createBitmap(v.getDrawingCache(), 0, 0, v.getMeasuredWidth(), v.getMeasuredHeight());
v.setDrawingCacheEnabled(false);
v.destroyDrawingCache();
return b;
}
开源方案
在滚动视图中，如果当前View并没有在视图中全部绘制出来，我们可以利用View的ScrollTo()和ScrollBy()方法来移动画布，同时获取当前View的可视部分的DrawingCache，最后进行拼接得到其Bitmap，参考: PGSSoft/scrollscreenshot@[Github] 。
Scrollview截屏
三个截屏中，ScrollView最简单，因为ScrollView只有一个childView，虽然没有全部显示在界面上，但是已经全部渲染绘制，因此可以直接 调用 scrollView.draw(canvas) 来完成截图
public static Bitmap shotScrollView(ScrollView scrollView) {
int h = 0;
Bitmap bitmap = null;
for (int i = 0; i < scrollView.getChildCount(); i++) {
h += scrollView.getChildAt(i).getHeight();
scrollView.getChildAt(i).setBackgroundColor(Color.parseColor("#ffffff"));
}
bitmap = Bitmap.createBitmap(scrollView.getWidth(), h, Bitmap.Config.RGB_565);
final Canvas canvas = new Canvas(bitmap);
scrollView.draw(canvas);
return bitmap;
}
Scrollview截屏
而ListView就是会回收与重用Item，并且只会绘制在屏幕上显示的ItemView，根据stackoverflow上大神的建议，采用一个List来存储Item的视图，这种方案依然不够好，当Item足够多的时候，可能会发生oom。
public static Bitmap shotListView(ListView listview) {
ListAdapter adapter = listview.getAdapter();
int itemscount = adapter.getCount();
int allitemsheight = 0;
List bmps = new ArrayList();
for (int i = 0; i < itemscount; i++) {
View childView = adapter.getView(i, null, listview);
childView.measure(
View.MeasureSpec.makeMeasureSpec(listview.getWidth(), View.MeasureSpec.EXACTLY),
View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED));
childView.layout(0, 0, childView.getMeasuredWidth(), childView.getMeasuredHeight());
childView.setDrawingCacheEnabled(true);
childView.buildDrawingCache();
bmps.add(childView.getDrawingCache());
allitemsheight += childView.getMeasuredHeight();
}
Bitmap bigbitmap =
Bitmap.createBitmap(listview.getMeasuredWidth(), allitemsheight, Bitmap.Config.ARGB_8888);
Canvas bigcanvas = new Canvas(bigbitmap);
Paint paint = new Paint();
int iHeight = 0;
for (int i = 0; i < bmps.size(); i++) {
Bitmap bmp = bmps.get(i);
bigcanvas.drawBitmap(bmp, 0, iHeight, paint);
iHeight += bmp.getHeight();
bmp.recycle();
bmp = null;
}
return bigbitmap;
}
RecyclerView截屏
我们都知道，在新的Android版本中，已经可以用RecyclerView来代替使用ListView的场景，相比较ListView，RecyclerView对Item View的缓存支持的更好。可以采用和ListView相同的方案，这里也是在stackoverflow上看到的方案。
public static Bitmap shotRecyclerView(RecyclerView view) {
RecyclerView.Adapter adapter = view.getAdapter();
Bitmap bigBitmap = null;
if (adapter != null) {
int size = adapter.getItemCount();
int height = 0;
Paint paint = new Paint();
int iHeight = 0;
final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
// Use 1/8th of the available memory for this memory cache.
final int cacheSize = maxMemory / 8;
LruCache bitmaCache = new LruCache<>(cacheSize);
for (int i = 0; i < size; i++) {
RecyclerView.ViewHolder holder = adapter.createViewHolder(view, adapter.getItemViewType(i));
adapter.onBindViewHolder(holder, i);
holder.itemView.measure(
View.MeasureSpec.makeMeasureSpec(view.getWidth(), View.MeasureSpec.EXACTLY),
View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED));
holder.itemView.layout(0, 0, holder.itemView.getMeasuredWidth(),
holder.itemView.getMeasuredHeight());
holder.itemView.setDrawingCacheEnabled(true);
holder.itemView.buildDrawingCache();
Bitmap drawingCache = holder.itemView.getDrawingCache();
if (drawingCache != null) {
bitmaCache.put(String.valueOf(i), drawingCache);
}
height += holder.itemView.getMeasuredHeight();
}
bigBitmap = Bitmap.createBitmap(view.getMeasuredWidth(), height, Bitmap.Config.ARGB_8888);
Canvas bigCanvas = new Canvas(bigBitmap);
Drawable lBackground = view.getBackground();
if (lBackground instanceof ColorDrawable) {
ColorDrawable lColorDrawable = (ColorDrawable) lBackground;
int lColor = lColorDrawable.getColor();
bigCanvas.drawColor(lColor);
}
for (int i = 0; i < size; i++) {
Bitmap bitmap = bitmaCache.get(String.valueOf(i));
bigCanvas.drawBitmap(bitmap, 0f, iHeight, paint);
iHeight += bitmap.getHeight();
bitmap.recycle();
}
}
return bigBitmap;
}
上面的方法在截取存在异步加载图片的RecyclerView时候会出现加载不出图片的情况,这里再补充一种滚动式截屏的方法
public static void screenShotRecycleView(final RecyclerView mRecyclerView, final
RecycleViewRecCallback callBack) {
if (mRecyclerView == null) {
return;
}
baseListFragment.MyAdapter adapter = (baseListFragment.MyAdapter) mRecyclerView.getAdapter();
final Paint paint = new Paint();
final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
// Use 1/8th of the available memory for this memory cache.
final int cacheSize = maxMemory / 8;
LruCache bitmaCache = new LruCache<>(cacheSize);
final int oneScreenHeight = mRecyclerView.getMeasuredHeight();
int shotHeight = 0;
if (adapter != null && adapter.getData().size() > 0) {
int headerSize = adapter.getHeaderLayoutCount();
int dataSize = adapter.getData().size();
for (int i = 0; i < headerSize + dataSize; i++) {
baseViewHolder holder = (baseViewHolder) adapter.createViewHolder(mRecyclerView, adapter.getItemViewType(i));
if (i >= headerSize)
adapter.startConvert(holder, adapter.getData().get(i - headerSize));
holder.itemView.measure(
View.MeasureSpec.makeMeasureSpec(mRecyclerView.getWidth(), View.MeasureSpec.EXACTLY),
View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED));
holder.itemView.layout(0, 0, holder.itemView.getMeasuredWidth(), holder.itemView.getMeasuredHeight());
holder.itemView.setDrawingCacheEnabled(true);
holder.itemView.buildDrawingCache();
Bitmap drawingCache = holder.itemView.getDrawingCache();
//holder.itemView.destroyDrawingCache();//释放缓存占用的资源
if (drawingCache != null) {
bitmaCache.put(String.valueOf(i), drawingCache);
}
shotHeight += holder.itemView.getHeight();
if (shotHeight > 12000) {
//设置截图最大值
if (callBack != null)
callBack.onRecFinished(null);
return;
}
}
//添加底部高度(加载更多或loading布局高度,此处为固定值:)
final int footHight = Util.dip2px(mRecyclerView.getContext(), 42);
shotHeight += footHight;
//返回到顶部
while (mRecyclerView.canScrollVertically(-1)) {
mRecyclerView.scrollBy(0, -oneScreenHeight);
}
//绘制截图的背景
final Bitmap bigBitmap = Bitmap.createBitmap(mRecyclerView.getMeasuredWidth(), shotHeight, Bitmap.Config.ARGB_8888);
final Canvas bigCanvas = new Canvas(bigBitmap);
Drawable lBackground = mRecyclerView.getBackground();
if (lBackground instanceof ColorDrawable) {
ColorDrawable lColorDrawable = (ColorDrawable) lBackground;
int lColor = lColorDrawable.getColor();
bigCanvas.drawColor(lColor);
}
final int[] drawOffset = {0};
final Canvas canvas = new Canvas();
if (shotHeight <= oneScreenHeight) {
//仅有一页
Bitmap bitmap = Bitmap.createBitmap(mRecyclerView.getWidth(), mRecyclerView.getHeight(), Bitmap.Config.ARGB_8888);
canvas.setBitmap(bitmap);
mRecyclerView.draw(canvas);
if (callBack != null)
callBack.onRecFinished(bitmap);
} else {
//超过一页
final int finalShotHeight = shotHeight;
mRecyclerView.postDelayed(new Runnable() {
@Override
public void run() {
if ((drawOffset[0] + oneScreenHeight < finalShotHeight)) {
//超过一屏
Bitmap bitmap = Bitmap.createBitmap(mRecyclerView.getWidth(), mRecyclerView.getHeight(), Bitmap.Config.ARGB_8888);
canvas.setBitmap(bitmap);
mRecyclerView.draw(canvas);
bigCanvas.drawBitmap(bitmap, 0, drawOffset[0], paint);
drawOffset[0] += oneScreenHeight;
mRecyclerView.scrollBy(0, oneScreenHeight);
try {
bitmap.recycle();
} catch (Exception ex) {
ex.printStackTrace();
}
mRecyclerView.postDelayed(this, 10);
} else {
//不足一屏时的处理
int leftHeight = finalShotHeight - drawOffset[0] - footHight;
mRecyclerView.scrollBy(0, leftHeight);
int top = oneScreenHeight - (finalShotHeight - drawOffset[0]);
if (top > 0 && leftHeight > 0) {
Bitmap bitmap = Bitmap.createBitmap(mRecyclerView.getWidth(), mRecyclerView.getHeight(), Bitmap.Config.ARGB_8888);
canvas.setBitmap(bitmap);
mRecyclerView.draw(canvas);
//截图,只要补足的那块图
bitmap = Bitmap.createBitmap(bitmap, 0, top, bitmap.getWidth(), leftHeight, null, false);
bigCanvas.drawBitmap(bitmap, 0, drawOffset[0], paint);
try {
bitmap.recycle();
} catch (Exception ex) {
ex.printStackTrace();
}
}
if (callBack != null)
callBack.onRecFinished(bigBitmap);
}
}
}, 10);
}
}
}
public interface RecycleViewRecCallback {
void onRecFinished(Bitmap bitmap);
}
相信有不少小伙伴用BRVH第三方库来做recycleview的适配器的。使用这个库的话再用上面的方法会报角标越界的错误，看了BRVH的源码
public void onBindViewHolder(ViewHolder holder, int positions) {
int viewType = holder.getItemViewType();
switch(viewType) {
case 0:
this.convert((baseViewHolder)holder, this.mData.get(holder.getLayoutPosition() - this.getHeaderLayoutCount()));
case 273:
case 819:
case 1365:
break;
case 546:
this.addLoadMore(holder);
break;
default:
this.convert((baseViewHolder)holder, this.mData.get(holder.getLayoutPosition() - this.getHeaderLayoutCount()));
this.onBindDefViewHolder((baseViewHolder)holder, this.mData.get(holder.getLayoutPosition() - this.getHeaderLayoutCount()));
}
}
在调用 adapter.onBindViewHolder 时，因为里面的 position 参数未使用，里面用的计算 holder.getLayoutPosition() - this.getHeaderLayoutCount() 的值一直是-1导致角标越界报错。
本人理解，RecyclerView的截屏原理是，首先构造每个item的ViewHolder，然后调用具体设置数据到每个item的方法，此时cache中就存有item的内容，此时绘制就能获取到完整的内容。采用v7包中的 onBindViewHolder 方法即可，或者是BRVH的 convert 方法，可以看到BRVH中没有暴露出这个方法，而且唯一暴露出的 onBindViewHolder 还会报角标越界错误，此时我们就需要在BRVH的基础上暴露出 convert 即可，代码如下
public class MyAdapter extends baseQuickAdapter{ public MyAdapter() { super(getItemLayoutResId(), datas); } public void startConvert(baseViewHolder viewHolder, T t){ convert(viewHolder,t); } @Override protected void convert(baseViewHolder viewHolder, T t) { bindView(viewHolder, t); } }
然后将上面所述的获取Bitmap方法修改一下
public static Bitmap getRecyclerViewScreenshot(RecyclerView view) {
baseListFragment.MyAdapter adapter = (baseListFragment.MyAdapter) view.getAdapter();
Bitmap bigBitmap = null;
if (adapter != null) {
int size = adapter.getData().size();
int height = 0;
Paint paint = new Paint();
int iHeight = 0;
final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
// Use 1/8th of the available memory for this memory cache.
final int cacheSize = maxMemory / 8;
LruCache bitmaCache = new LruCache<>(cacheSize);
for (int i = 0; i < size; i++) {
baseViewHolder holder = (baseViewHolder) adapter.createViewHolder(view, adapter.getItemViewType(i));
//此处需要调用convert方法，否则绘制出来的都是空的item
adapter.startConvert(holder, adapter.getData().get(i));
holder.itemView.measure(
View.MeasureSpec.makeMeasureSpec(view.getWidth(), View.MeasureSpec.EXACTLY),
View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED));
holder.itemView.layout(0, 0, holder.itemView.getMeasuredWidth(),
holder.itemView.getMeasuredHeight());
holder.itemView.setDrawingCacheEnabled(true);
holder.itemView.buildDrawingCache();
Bitmap drawingCache = holder.itemView.getDrawingCache();
if (drawingCache != null) {
bitmaCache.put(String.valueOf(i), drawingCache);
}
height += holder.itemView.getMeasuredHeight();
}
bigBitmap = Bitmap.createBitmap(view.getMeasuredWidth(), height, Bitmap.Config.ARGB_8888);
Canvas bigCanvas = new Canvas(bigBitmap);
Drawable lBackground = view.getBackground();
if (lBackground instanceof ColorDrawable) {
ColorDrawable lColorDrawable = (ColorDrawable) lBackground;
int lColor = lColorDrawable.getColor();
bigCanvas.drawColor(lColor);
}
for (int i = 0; i < size; i++) {
Bitmap bitmap = bitmaCache.get(String.valueOf(i));
bigCanvas.drawBitmap(bitmap, 0f, iHeight, paint);
iHeight += bitmap.getHeight();
bitmap.recycle();
}
}
return bigBitmap;
}
合成Bitmap
比如四张合成一张
public static Bitmap combineBitmapsIntoonlyOne(Bitmap pic1, Bitmap pic2, Bitmap pic3, Bitmap pic4, Activity context) {
int w_total = pic2.getWidth();
int h_total = pic1.getHeight() + pic2.getHeight() + pic3.getHeight() + pic4.getHeight();
int h_pic1 = pic1.getHeight();
int h_pic4 = pic4.getHeight();
int h_pic12 = pic1.getHeight() + pic2.getHeight();
//此处为防止OOM需要对高度做限制
if (h_total > HEIGHTLIMIT) {
return null;
}
Bitmap only_bitmap = Bitmap.createBitmap(w_total, h_total, Bitmap.Config.ARGB_4444);
Canvas canvas = new Canvas(only_bitmap);
canvas.drawColor(ContextCompat.getColor(context, R.color.color_content_bg));
canvas.drawBitmap(pic1, 0, 0, null);
canvas.drawBitmap(pic2, 0, h_pic1, null);
canvas.drawBitmap(pic3, 0, h_pic12, null);
canvas.drawBitmap(pic4, 0, h_total - h_pic4, null);
return only_bitmap;
}
图片后期处理
public static void savingBitmapIntoFile(final Bitmap pic1, final Bitmap pic2, final Activity context, final BitmapAndFileCallBack callBack) {
if (context == null || context.isFinishing()) {
return;
}
Thread thread = new Thread(new Runnable() {
@Override
public void run() {
String fileReturnPath = "";
int w = pic1.getWidth();
Bitmap bottom = BitmapFactory.decodeResource(context.getResources(), R.drawable.ic_picture_combine_bottom);
Bitmap top_banner = BitmapFactory.decodeResource(context.getResources(), R.drawable.ic_picture_combine_top);
Bitmap bitmap_bottom = anyRatioCompressing(bottom, (float) w / bottom.getWidth(), (float) w / bottom.getWidth());
Bitmap bitmap_top = anyRatioCompressing(top_banner, (float) w / bottom.getWidth(), (float) w / bottom.getWidth());
final Bitmap only_bitmap = combineBitmapsIntoonlyOne(bitmap_top, pic1, pic2, bitmap_bottom, context);
// 获取当前时间
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd-HH-mm-ss-ms", Locale.getDefault());
String data = sdf.format(new Date());
// 获取内存路径
// 设置图片路径+命名规范
// 声明输出文件
String storagePath = Environment.getExternalStorageDirectory().getAbsolutePath();
String fileTitle = "Screenshot_" + data + "_com.bertadata.qxb.biz_info.jpg";
String filePath = storagePath + "/DCIM/";
final String fileAbsolutePath = filePath + fileTitle;
File file = new File(fileAbsolutePath);
if (only_bitmap != null) {
try {
// 首先，对原图进行一步质量压缩,形成初步文件
FileOutputStream fos = new FileOutputStream(file);
only_bitmap.compress(Bitmap.CompressFormat.JPEG, 50, fos);
// 另建一个文件other_file预备输出
String other_fileTitle = "Screenshot_" + data + "_com.bertadata.qxb.jpg";
String other_fileAbsolutePath = filePath + other_fileTitle;
File other_file = new File(other_fileAbsolutePath);
FileOutputStream other_fos = new FileOutputStream(other_file);
// 其次，要判断质压之后的文件大小，按文件大小分级进行处理
long file_size = file.length() / 1024; // size of file(KB)
if (file_size < 0 || !(file.exists())) {
// 零级： 文件判空
throw new NullPointerException();
} else if (file_size > 0 && file_size <= 256) {
// 一级： 直接输出
deleteFile(other_file);
// 通知刷新文件系统，显示最新截取的图文件
fileReturnPath = fileAbsolutePath;
context.sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, Uri.parse("file://" + fileAbsolutePath)));
} else if (file_size > 256 && file_size <= 768) {
// 二级： 简单压缩:压缩为原比例的3/4，质压为50%
anyRatioCompressing(only_bitmap, (float) 3 / 4, (float) 3 / 4).compress(Bitmap.CompressFormat.JPEG, 40, other_fos);
deleteFile(file);
// 通知刷新文件系统，显示最新截取的图文件
fileReturnPath = other_fileAbsolutePath;
context.sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, Uri.parse("file://" + other_fileAbsolutePath)));
} else if (file_size > 768 && file_size <= 1280) {
// 三级： 中度压缩：压缩为原比例的1/2，质压为40%
anyRatioCompressing(only_bitmap, (float) 1 / 2, (float) 1 / 2).compress(Bitmap.CompressFormat.JPEG, 40, other_fos);
deleteFile(file);
// 通知刷新文件系统，显示最新截取的图文件
fileReturnPath = other_fileAbsolutePath;
context.sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, Uri.parse("file://" + other_fileAbsolutePath)));
} else if (file_size > 1280 && file_size <= 2048) {
// 四级： 大幅压缩：压缩为原比例的1/3，质压为40%
anyRatioCompressing(only_bitmap, (float) 1 / 3, (float) 1 / 3).compress(Bitmap.CompressFormat.JPEG, 40, other_fos);
deleteFile(file);
// 通知刷新文件系统，显示最新截取的图文件
fileReturnPath = other_fileAbsolutePath;
context.sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, Uri.parse("file://" + other_fileAbsolutePath)));
} else if (file_size > 2048) {
// 五级： 中度压缩：压缩为原比例的1/2，质压为40%
anyRatioCompressing(only_bitmap, (float) 1 / 2, (float) 1 / 2).compress(Bitmap.CompressFormat.JPEG, 40, other_fos);
deleteFile(file);
// 通知刷新文件系统，显示最新截取的图文件
fileReturnPath = other_fileAbsolutePath;
context.sendBroadcast(new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, Uri.parse("file://" + other_fileAbsolutePath)));
}
// 注销fos;
fos.flush();
other_fos.flush();
other_fos.close();
fos.close();
//callback用于回传保存成功的路径以及Bitmap
callBack.onSuccess(only_bitmap, fileReturnPath);
} catch (Exception e) {
e.printStackTrace();
}
} else callBack.onSuccess(null, "");
}
});
thread.start();
}
public static Bitmap anyRatioCompressing(Bitmap bitmap, float width_ratio, float height_ratio) {
Matrix matrix = new Matrix();
matrix.postScale(width_ratio, height_ratio);
return Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, false);
}
总结
以上所述是小编给大家介绍的Android截屏方案实现原理解析，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的。在此也非常感谢大家对考高分网网站的支持！
