android camerax怎样处理预览

Android CameraX 是一个用于简化 Android 相机功能开发的库。要处理预览，您需要遵循以下步骤：

1. 添加依赖项

在您的 build.gradle 文件中添加 CameraX 和 CameraX LiveData 依赖项：

dependencies {
    implementation 'androidx.camera:camera-core:1.0.0'
    implementation 'androidx.camera:camera-camera2:1.0.0'
    implementation 'androidx.camera:camera-lifecycle:1.0.0'
    implementation 'androidx.camera:camera-view:1.0.0'
    implementation 'androidx.lifecycle:lifecycle-livedata-ktx:2.3.1'
}

2. 配置 CameraX

在您的应用模块（通常是 MainActivity）中，配置 CameraX：

import android.Manifest
import android.content.pm.PackageManager
import androidx.appcompat.app.AppCompatActivity
import androidx.camera.core.CameraSelector
import androidx.camera.core.ImageAnalysis
import androidx.camera.core.ImageProxy
import androidx.camera.lifecycle.ProcessCameraProvider
import androidx.core.app.ActivityCompat
import androidx.core.content.ContextCompat
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.launch

class MainActivity : AppCompatActivity() {

    private lateinit var cameraProviderFuture: ProcessCameraProvider
    private lateinit var imageAnalyzer: ImageAnalyzer

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // 检查相机权限
        if (hasCameraPermission()) {
            // 获取 CameraProvider
            cameraProviderFuture = ProcessCameraProvider.getInstance(this)
            // 创建 ImageAnalyzer
            imageAnalyzer = ImageAnalyzer()
            // 设置预览
            setupPreview()
        } else {
            requestCameraPermission()
        }
    }

    private fun hasCameraPermission(): Boolean {
        return ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA) == PackageManager.PERMISSION_GRANTED
    }

    private fun requestCameraPermission() {
        ActivityCompat.requestPermissions(this, arrayOf(Manifest.permission.CAMERA), REQUEST_CAMERA_PERMISSION)
    }

    private fun setupPreview() {
        cameraProviderFuture.addListener({
            val cameraProvider = cameraProviderFuture.get()
            bindPreview(cameraProvider)
        }, ContextCompat.getMainExecutor(this))
    }

    private fun bindPreview(cameraProvider: ProcessCameraProvider) {
        val preview = androidx.camera.core.Preview.Builder().build()
        preview.setSurfaceProvider(findViewById<androidx.camera.core.PreviewView>(R.id.previewView).surfaceProvider)

        val cameraSelector = CameraSelector.Builder().requireLensFacing(CameraSelector.LENS_FACING_BACK).build()

        cameraProvider.unbindAll()
        cameraProvider.bindToLifecycle(this, cameraSelector, preview, imageAnalyzer)
    }

    override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<out String>, grantResults: IntArray) {
        when (requestCode) {
            REQUEST_CAMERA_PERMISSION -> {
                if (grantResults.isNotEmpty() && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    setupPreview()
                } else {
                    // 处理权限被拒绝的情况
                }
            }
        }
    }

    companion object {
        private const val REQUEST_CAMERA_PERMISSION = 1
    }
}

3. 创建预览视图

在您的布局文件（例如 activity_main.xml）中，添加一个 PreviewView：

<androidx.camera.core.PreviewView
    android:id="@+id/previewView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

4. 创建图像分析器

创建一个继承自 ImageAnalyzer 的类，并实现 ImageProxy.Listener 接口。在这个类中，您可以处理图像数据，例如使用机器学习模型进行物体识别。

import android.graphics.ImageFormat
import android.os.Build
import android.renderscript.Allocation
import android.renderscript.Element
import android.renderscript.RenderScript
import android.renderscript.ScriptIntrinsicBlur
import androidx.camera.core.ImageProxy
import java.nio.ByteBuffer

class ImageAnalyzer : ImageAnalyzer() {

    private val scriptIntrinsicBlur = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs))

    override fun analyze(imageProxy: ImageProxy) {
        if (imageProxy.image == null) {
            return
        }

        val mediaImage = imageProxy.image!!
        val buffer = mediaImage.planes[0].buffer
        val byteArray = ByteArray(buffer.capacity())
        buffer.get(byteArray)

        // 将字节数组转换为 Bitmap
        val bitmap = BitmapFactory.decodeByteArray(byteArray, 0, byteArray.size)

        // 使用 RenderScript 进行模糊处理
        val input = Allocation.createFromBitmap(rs, bitmap)
        val output = Allocation.createFromBitmap(rs, bitmap)
        scriptIntrinsicBlur.setRadius(15f)
        scriptIntrinsicBlur.setInput(input)
        scriptIntrinsicBlur.forEach(output)
        output.copyTo(bitmap)

        // 将处理后的 Bitmap 转换回字节数组
        val outputBuffer = output.getBuffer()
        outputBuffer.get(byteArray)

        // 处理图像数据（例如上传到服务器或显示在 UI 上）
    }
}

现在，当您运行应用时，CameraX 应该会处理预览并将图像传递给 ImageAnalyzer 类进行分析。