public GenericRequestBuilder<ModelType, DataType, ResourceType, TranscodeType> placeholder(
            Drawable drawable) {
        this.placeholderDrawable = drawable;

        return this;
    }
Sets an {@link Drawable} to display while a resource is loading.

@param drawable The drawable to display as a placeholder.
@return This request builder.
core/src/main/java/com/bumptech/glide/GenericRequestBuilder.java