更新：

我们还可以使用renderscript API来模糊API级别〉= 17的背景，并使用fastblur来模糊API级别〈17的背景。下面是Github项目。
- Github Project
- Blog

使用FastBlur的步骤

1)使用下面的代码拍摄您的背景快照

private static Bitmap takeScreenShot(Activity activity)
    {
        View view = activity.getWindow().getDecorView();
        view.setDrawingCacheEnabled(true);
        view.buildDrawingCache();
        Bitmap b1 = view.getDrawingCache();
        Rect frame = new Rect();
        activity.getWindow().getDecorView().getWindowVisibleDisplayFrame(frame);
        int statusBarHeight = frame.top;
        int width = activity.getWindowManager().getDefaultDisplay().getWidth();
        int height = activity.getWindowManager().getDefaultDisplay().getHeight();

        Bitmap b = Bitmap.createBitmap(b1, 0, statusBarHeight, width, height  - statusBarHeight);
        view.destroyDrawingCache();
        return b;
    }

这样使用Bitmap map=takeScreenShot(BlurImageView.this);//您的活动名称
2)调用方法Bitmap fast=fastblur(map, 10);从Here获取

public Bitmap fastblur(Bitmap sentBitmap, int radius) {
        Bitmap bitmap = sentBitmap.copy(sentBitmap.getConfig(), true);

        if (radius < 1) {
            return (null);
        }

        int w = bitmap.getWidth();
        int h = bitmap.getHeight();

        int[] pix = new int[w * h];
        Log.e("pix", w + " " + h + " " + pix.length);
        bitmap.getPixels(pix, 0, w, 0, 0, w, h);

        int wm = w - 1;
        int hm = h - 1;
        int wh = w * h;
        int div = radius + radius + 1;

        int r[] = new int[wh];
        int g[] = new int[wh];
        int b[] = new int[wh];
        int rsum, gsum, bsum, x, y, i, p, yp, yi, yw;
        int vmin[] = new int[Math.max(w, h)];

        int divsum = (div + 1) >> 1;
        divsum *= divsum;
        int dv[] = new int[256 * divsum];
        for (i = 0; i < 256 * divsum; i++) {
            dv[i] = (i / divsum);
        }

        yw = yi = 0;

        int[][] stack = new int[div][3];
        int stackpointer;
        int stackstart;
        int[] sir;
        int rbs;
        int r1 = radius + 1;
        int routsum, goutsum, boutsum;
        int rinsum, ginsum, binsum;

        for (y = 0; y < h; y++) {
            rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;
            for (i = -radius; i <= radius; i++) {
                p = pix[yi + Math.min(wm, Math.max(i, 0))];
                sir = stack[i + radius];
                sir[0] = (p & 0xff0000) >> 16;
            sir[1] = (p & 0x00ff00) >> 8;
        sir[2] = (p & 0x0000ff);
        rbs = r1 - Math.abs(i);
        rsum += sir[0] * rbs;
        gsum += sir[1] * rbs;
        bsum += sir[2] * rbs;
        if (i > 0) {
            rinsum += sir[0];
            ginsum += sir[1];
            binsum += sir[2];
        } else {
            routsum += sir[0];
            goutsum += sir[1];
            boutsum += sir[2];
        }
            }
            stackpointer = radius;

            for (x = 0; x < w; x++) {

                r[yi] = dv[rsum];
                g[yi] = dv[gsum];
                b[yi] = dv[bsum];

                rsum -= routsum;
                gsum -= goutsum;
                bsum -= boutsum;

                stackstart = stackpointer - radius + div;
                sir = stack[stackstart % div];

                routsum -= sir[0];
                goutsum -= sir[1];
                boutsum -= sir[2];

                if (y == 0) {
                    vmin[x] = Math.min(x + radius + 1, wm);
                }
                p = pix[yw + vmin[x]];

                sir[0] = (p & 0xff0000) >> 16;
            sir[1] = (p & 0x00ff00) >> 8;
            sir[2] = (p & 0x0000ff);

            rinsum += sir[0];
            ginsum += sir[1];
            binsum += sir[2];

            rsum += rinsum;
            gsum += ginsum;
            bsum += binsum;

            stackpointer = (stackpointer + 1) % div;
            sir = stack[(stackpointer) % div];

            routsum += sir[0];
            goutsum += sir[1];
            boutsum += sir[2];

            rinsum -= sir[0];
            ginsum -= sir[1];
            binsum -= sir[2];

            yi++;
            }
            yw += w;
        }
        for (x = 0; x < w; x++) {
            rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;
            yp = -radius * w;
            for (i = -radius; i <= radius; i++) {
                yi = Math.max(0, yp) + x;

                sir = stack[i + radius];

                sir[0] = r[yi];
                sir[1] = g[yi];
                sir[2] = b[yi];

                rbs = r1 - Math.abs(i);

                rsum += r[yi] * rbs;
                gsum += g[yi] * rbs;
                bsum += b[yi] * rbs;

                if (i > 0) {
                    rinsum += sir[0];
                    ginsum += sir[1];
                    binsum += sir[2];
                } else {
                    routsum += sir[0];
                    goutsum += sir[1];
                    boutsum += sir[2];
                }

                if (i < hm) {
                    yp += w;
                }
            }
            yi = x;
            stackpointer = radius;
            for (y = 0; y < h; y++) {
                // Preserve alpha channel: ( 0xff000000 & pix[yi] )
                pix[yi] = ( 0xff000000 & pix[yi] ) | ( dv[rsum] << 16 ) | ( dv[gsum] << 8 ) | dv[bsum];

                rsum -= routsum;
                gsum -= goutsum;
                bsum -= boutsum;

                stackstart = stackpointer - radius + div;
                sir = stack[stackstart % div];

                routsum -= sir[0];
                goutsum -= sir[1];
                boutsum -= sir[2];

                if (x == 0) {
                    vmin[y] = Math.min(y + r1, hm) * w;
                }
                p = x + vmin[y];

                sir[0] = r[p];
                sir[1] = g[p];
                sir[2] = b[p];

                rinsum += sir[0];
                ginsum += sir[1];
                binsum += sir[2];

                rsum += rinsum;
                gsum += ginsum;
                bsum += binsum;

                stackpointer = (stackpointer + 1) % div;
                sir = stack[stackpointer];

                routsum += sir[0];
                goutsum += sir[1];
                boutsum += sir[2];

                rinsum -= sir[0];
                ginsum -= sir[1];
                binsum -= sir[2];

                yi += w;
            }
        }

        Log.e("pix", w + " " + h + " " + pix.length);
        bitmap.setPixels(pix, 0, w, 0, 0, w, h);

        return (bitmap);
    }

3)最后在Button上单击

btnblur.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View view) {

                AlertDialog.Builder builder=new AlertDialog.Builder(BlurImageView.this,R.style.Theme_D1NoTitleDim);
                builder.setTitle("Content");
                builder.setMessage("CLICK OK to Exit");
                builder.setPositiveButton("ON", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        back_dim_layout.setVisibility(View.GONE);
                        dialog.cancel();
                    }
                });
                alert=builder.create();
                Bitmap map=takeScreenShot(BlurImageView.this);

                Bitmap fast=fastblur(map, 10);
                final Drawable draw=new BitmapDrawable(getResources(),fast);
                alert.getWindow().setBackgroundDrawable(draw);
                alert.show();
            }
        });

That's It Now You can see the Blur Image Behind You活动
希望这能对任何人都有帮助…

这个来自nitesh的解决方案的工作方式如下

但如果你不能让你的警报到中心（像我一样），也检查我的答案，这是Here
我所做的是
使用了两个alertDialogs一个是模糊效果（使用getWindow()），现在没有显示（我删除了它的setContentView/可以使用透明背景）
另一个是真实的的alertDialog在模糊效果后得到的显示

输出

对于快速模糊和解决对话框出现在屏幕顶部的问题，我认为有一个更简单的解决方案：

// Custom Dialog to be called in the Activity choosed.
public class CustomDialog {
    private Dialog dialog;

    public CustomDialog(AppCompatActivity activity) {
        dialog = new Dialog(activity);
        dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
        View viewCustomDialog = LayoutInflater.from(activity).inflate(R.layout.custom_dialog, null);
        dialog.setContentView(viewCustomDialog);

        RelativeLayout rootView = viewCustomDialog.findViewById(R.id.rootView);

        WindowManager.LayoutParams layoutParams = new WindowManager.LayoutParams();
        layoutParams.width = WindowManager.LayoutParams.MATCH_PARENT;
        layoutParams.height = WindowManager.LayoutParams.WRAP_CONTENT;
        layoutParams.gravity = Gravity.CENTER;
        dialog.getWindow().setAttributes(layoutParams);

        // First get bitmap with blur filter applied, using the function blur presented here,  
        // or another function.
        // Activity parameter is the Activity for which you call dialog.show();
        Bitmap bitmap = Utils.blur(activity);

        // Get bitmap height.
        int bitmapHeight = bitmap.getHeight();

        dialog.setOnShowListener(dialogInterface -> {
            // When dialog is shown, before set new blurred image for background drawable, 
            // the root view height and dialog margin are saved.
            int rootViewHeight = rootView.getHeight();
            int marginLeftAndRight = dialog.getWindow().getDecorView().getPaddingLeft();

            // Set new blurred image for background drawable.
            dialog.getWindow().setBackgroundDrawable(new BitmapDrawable(builder.context.getResources(), bitmap));

            // After get positions and heights, recover and rebuild original marginTop position, 
            // that is (bitmapHeight - rootViewHeight) / 2.
            // Also recover and rebuild Dialog original left and right margin.
            FrameLayout.LayoutParams rootViewLayoutParams = (FrameLayout.LayoutParams)rootView.getLayoutParams();
            rootViewLayoutParams.setMargins(marginLeftAndRight, (bitmapHeight - rootViewHeight) / 2, marginLeftRight, 0);
        });

        dialog.show();
    }
}

模糊方法：

public static Bitmap blur(AppCompatActivity activity) {
   Bitmap bitmap = Utils.takeScreenShot(activity);

   RenderScript renderScript = RenderScript.create(activity);

   // This will blur the bitmapOriginal with a radius of 16 and save it in bitmapOriginal
   final Allocation input = Allocation.createFromBitmap(renderScript, bitmap); // Use this constructor for best performance, because it uses USAGE_SHARED mode which reuses memory
   final Allocation output = Allocation.createTyped(renderScript, input.getType());
   final ScriptIntrinsicBlur script = ScriptIntrinsicBlur.create(renderScript, Element.U8_4(renderScript));
   script.setRadius(16f);
   script.setInput(input);
   script.forEach(output);
   output.copyTo(bitmap);

   return bitmap;
}

TakeScreenShot方法：

public static Bitmap takeScreenShot(AppCompatActivity activity) {
    View view = activity.getWindow().getDecorView();
    view.setDrawingCacheEnabled(true);
    view.buildDrawingCache();
    Bitmap bitmap = view.getDrawingCache();
    Rect frame = new Rect();
    activity.getWindow().getDecorView().getWindowVisibleDisplayFrame(frame);
    int statusBarHeight = frame.top;
    int[] widthHeight = getScreenSize(activity);
    Bitmap bitmapResult = Bitmap.createBitmap(bitmap, 0, statusBarHeight, widthHeight[0], widthHeight[1]  - statusBarHeight);
    view.destroyDrawingCache();
    return bitmapResult;
}

GetScreenSize方法：

public static int[] getScreenSize(Context context) {
    int[] widthHeight = new int[2];
    widthHeight[WIDTH_INDEX] = 0;
    widthHeight[HEIGHT_INDEX] = 0;

    WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
    Display display = windowManager.getDefaultDisplay();

    Point size = new Point();
    display.getSize(size);
    widthHeight[WIDTH_INDEX] = size.x;
    widthHeight[HEIGHT_INDEX] = size.y;

    if (!isScreenSizeRetrieved(widthHeight)) {
        DisplayMetrics metrics = new DisplayMetrics();
        display.getMetrics(metrics);
        widthHeight[0] = metrics.widthPixels;
        widthHeight[1] = metrics.heightPixels;
    }

    if (!isScreenSizeRetrieved(widthHeight)) {
        widthHeight[0] = display.getWidth(); // deprecated
        widthHeight[1] = display.getHeight(); // deprecated
    }

    return widthHeight;
}   

private static boolean isScreenSizeRetrieved(int[] widthHeight) {
    return widthHeight[WIDTH_INDEX] != 0 && widthHeight[HEIGHT_INDEX] != 0;
}

要使用RenderScript（To blur），必须在App的build.gradle中添加：

defaultConfig {
    ...     
    renderscriptTargetApi 19
    renderscriptSupportModeEnabled true
}

试试这个

dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
    dialog.setContentView(view);
    dialog.setCancelable(true);
    Window window = dialog.getWindow();
    WindowManager.LayoutParams wlp = window.getAttributes();

    wlp.gravity = Gravity.CENTER;
    wlp.flags &= WindowManager.LayoutParams.FLAG_DIM_BEHIND;
    window.setAttributes(wlp);
    dialog.getWindow().setLayout(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);
    dialog.show();
}

Dialog dialog = new Dialog(this); 
        alertDialogView = LayoutInflater.from(KycActivity.this).inflate(R.layout.indian_user_layout, null); 
dialog.setContentView(alertDialogView); 
    dialog.getWindow().setLayout(WindowManager.LayoutParams.MATCH_PARENT,WindowManager.LayoutParams.MATCH_PARENT); 
    dialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT)); 
    diaog.getWindow().addFlags(WindowManager.LayoutParams.FLAG_BLUR_BEHIND); 
    dialog.show();
        
        ------------------------------------------------------------------------