如何从里面引用lambda？

Question

我试图在onCreate方法中获取视图的高度,但我找不到任何方法来删除OnGlobalLayoutListener.

在Java(工作):

containerLayout.getViewTreeObserver.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {  
    @Override  
    public void onGlobalLayout() {  
        containerLayout.getViewTreeObserver().removeGlobalOnLayoutListener(this); 
        int width  = layout.getMeasuredWidth();
        int height = layout.getMeasuredHeight(); 

    }  
});

在Kotlin(不接受"这个"):

   containerLayout.viewTreeObserver.addOnGlobalLayoutListener {
            containerLayout.viewTreeObserver.removeOnGlobalLayoutListener(this)
            Toast.makeText(applicationContext, "size is "+ containerLayout.height,Toast.LENGTH_LONG).show()
        }

这个问题有没有参考或例子？谢谢.

Answer 1

不支持从内部引用lambda.

作为一种变通方法,您可以使用匿名对象而不是lambda SAM转换为Java功能接口OnGlobalLayoutListener:

containerLayout.viewTreeObserver.addOnGlobalLayoutListener(object: OnGlobalLayoutListener {
    override fun onGlobalLayout() {
        // your code here. `this` should work
    }
})

Answer 2

这样的扩展是怎么回事？

import android.annotation.SuppressLint
import android.os.Build
import android.view.View
import android.view.ViewTreeObserver

inline fun View.doOnGlobalLayout(crossinline action: (view: View) -> Unit) {
    val vto = viewTreeObserver
    vto.addOnGlobalLayoutListener(object : ViewTreeObserver.OnGlobalLayoutListener {
        @SuppressLint("ObsoleteSdkInt")
        @Suppress("DEPRECATION")
        override fun onGlobalLayout() {
            action(this@doOnGlobalLayout)
            when {
                vto.isAlive -> {
                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
                        vto.removeOnGlobalLayoutListener(this)
                    } else {
                        vto.removeGlobalOnLayoutListener(this)
                    }
                }
                else -> {
                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
                        viewTreeObserver.removeOnGlobalLayoutListener(this)
                    } else {
                        viewTreeObserver.removeGlobalOnLayoutListener(this)
                    }
                }
            }
        }
    })
}

最后，您可以直接从 View 调用 OnGlobalLayoutListener

val view: View = ...
view.doOnGlobalLayout {
  val width = view?.measuredWidth
  val height = view?.measuredHeight
}