Kotlin 如何使用 Android CameraX 自动对焦

使用当前的CameraX 1.0.0，您可以通过以下两种方式进行操作:

1. 每X秒自动对焦一次:

2. Focus on-tap:

    previewView.afterMeasured {
        previewView.setOnTouchListener { _, event ->
            return@setOnTouchListener when (event.action) {
                MotionEvent.ACTION_DOWN -> {
                    true
                }
                MotionEvent.ACTION_UP -> {
                    val factory: MeteringPointFactory = SurfaceOrientedMeteringPointFactory(
                        previewView.width.toFloat(), previewView.height.toFloat()
                    )
                    val autoFocusPoint = factory.createPoint(event.x, event.y)
                    try {
                        camera.cameraControl.startFocusAndMetering(
                            FocusMeteringAction.Builder(
                                autoFocusPoint,
                                FocusMeteringAction.FLAG_AF
                            ).apply {
                                //focus only when the user tap the preview
                                disableAutoCancel()
                            }.build()
                        )
                    } catch (e: CameraInfoUnavailableException) {
                        Log.d("ERROR", "cannot access camera", e)
                    }
                    true
                }
                else -> false // Unhandled event.
            }
        }
    }
   

afterMeasured扩展函数是一个简单的实用程序:(感谢ch271828n提供improving it)

inline fun View.afterMeasured(crossinline block: () -> Unit) {
    if (measuredWidth > 0 && measuredHeight > 0) {
        block()
    } else {
        viewTreeObserver.addOnGlobalLayoutListener(object : ViewTreeObserver.GlobalLayoutListener {
            override fun onGlobalLayout() {
                if (measuredWidth > 0 && measuredHeight > 0) {
                    viewTreeObserver.removeOnGlobalLayoutListener(this)
                    block()
                } 
            }
        })
    }
}

使用以下命令可以获得Camera个对象

val camera = cameraProvider.bindToLifecycle(
    this@Activity, cameraSelector, previewView //this is a PreviewView
)