基于Anko与Kotlin的自定义RatingBar设置评分不生效问题求助

Hey there! Let's tackle why your custom StarRatingView isn't showing the 3-star rating when you call setRating(3) in your Anko layout. This is a common gotcha with Anko's DSL and custom Views, so let's break down the likely issues and fixes.

Common Causes & Solutions #

1. Your Custom RatingBar Isn't Triggering UI Updates #

First, check if your StarRatingView properly handles rating changes. When you call setRating(), you need to ensure the View redraws itself to reflect the new value.

Here's a corrected version of your custom RatingBar:

class StarRatingView @JvmOverloads constructor(
    context: Context,
    attrs: AttributeSet? = null,
    defStyleAttr: Int = android.R.attr.ratingBarStyle
) : RatingBar(context, attrs, defStyleAttr) {

    init {
        // Add your custom styling here (e.g., custom star drawables)
        val starDrawable = ContextCompat.getDrawable(context, R.drawable.custom_star)
        starDrawable?.let {
            progressDrawable = it
            secondaryProgressDrawable = it
            ratingDrawable = it
        }
    }

    override fun setRating(rating: Float) {
        super.setRating(rating)
        // Force the View to redraw with the new rating
        invalidate()
        // If your custom View has size changes, add requestLayout() too
        // requestLayout()
    }
}

The key here is calling invalidate() after setting the rating—this tells Android to redraw the View immediately.

2. Timing Issue in Anko DSL #

Anko creates Views quickly during layout inflation, and sometimes setRating() is called before the View is fully attached to the screen. In this case, the rating change doesn't trigger a redraw because the View isn't ready yet.

Fix this by using post() to delay the rating setting until the View is attached:

verticalLayout {
    starRatingView {
        // Post the rating update to the main thread's message queue
        post {
            setRating(3f)
        }
    }
}

post() ensures your setRating() call runs after the View has finished measuring and attaching to the window, so the change will be visible.

3. Missing or Incorrect Anko DSL Extension #

Double-check that you have a proper Anko extension function for your custom View. Without this, Anko might not initialize the View correctly:

// Add this at the top level or in a dedicated Anko extensions file
inline fun ViewManager.starRatingView(init: StarRatingView.() -> Unit): StarRatingView {
    return ankoView({ StarRatingView(it) }, theme = 0, init = init)
}

This extension lets Anko properly create and initialize your StarRatingView in the DSL.

4. Hardcoded Default Rating in Custom View #

Make sure you aren't setting a default rating in your StarRatingView's init block that overrides the value you set later. For example, avoid lines like setRating(0f) in the init unless that's intentional—this would overwrite your 3-star setting.

Test It Out #

Putting it all together, your MainActivity should look something like this:

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        verticalLayout {
            starRatingView {
                post {
                    setRating(3f)
                }
            }
        }
    }
}

This should correctly display a 3-star rating once the View is ready.

内容的提问来源于stack exchange，提问作者Blender