在我的案例中，解决方案是这样的:

final Drawable drawable = new ColorDrawable(android.graphics.Color.TRANSPARENT);
dialogAssignTag.getWindow().setBackgroundDrawable(drawable);

另外，在自定义对话框的xml文件中:

android:alpha="0.8"

添加以下代码

 dialog.getWindow().setBackgroundDrawable(new ColorDrawable(android.graphics.Color.TRANSPARENT));

或者换成这个:

dialog.getWindow().setBackgroundDrawableResource(android.R.color.transparent);

ColorDrawable drawable = new ColorDrawable(ContextCompat.getColor(ctx, android.R.color.transparent));
dialog.getWindow().setBackgroundDrawable(drawable);

对话框弹出填充默认的黑色背景颜色或主题颜色，所以你需要设置透明的背景到对话框。试试下面的代码:-

final Dialog dialog = new Dialog(this);
dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
dialog.getWindow().setBackgroundDrawable(new ColorDrawable(android.graphics.Color.TRANSPARENT));
dialog.setContentView(R.layout.splash);
dialog.show();

确保r.b ayout.themechanger没有背景色，因为默认情况下对话框有默认背景色。

你还需要添加dialog.getWindow().setBackgroundDrawable(newColorDrawable(Color.TRANSPARENT));

最后

<style name="TransparentDialog">
    <item name="android:windowIsFloating">true</item>
    <item name="android:windowNoTitle">true</item>
    <item name="android:windowBackground">@android:color/transparent</item>
    <item name="android:windowContentOverlay">@null</item>
    <item name="android:windowTitleStyle">@null</item>
</style>

你可以使用:

setBackgroundDrawable(null);

方法。下面是文档:

  /**
    * Set the background to a given Drawable, or remove the background. If the
    * background has padding, this View's padding is set to the background's
    * padding. However, when a background is removed, this View's padding isn't
    * touched. If setting the padding is desired, please use
    * {@link #setPadding(int, int, int, int)}.
    *
    * @param d The Drawable to use as the background, or null to remove the
    *        background
    */