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727 2023-04-03 03:53:53
Android CameraX 打开摄像头预览
目标很简单，用CameraX打开摄像头预览，实时显示在界面上。看看CameraX有没有Google说的那么好用。先按最简单的来，把预览显示出来。
引入依赖#
模块gradle的一些配置，使用的Android SDK版本为31，启用了databinding
apply plugin: 'com.android.application'apply plugin: 'kotlin-android'apply plugin: 'kotlin-android-extensions'apply plugin: 'kotlin-kapt'android { compileSdkVersion 31 buildToolsVersion "31.0.0" defaultConfig { minSdkVersion 21 targetSdkVersion 31 } dataBinding { enabled = true }}引入CameraX依赖（CameraX 核心库是用camera2实现的），目前主要用1.1.0-alpha11版本
dependencies { implementation "androidx.camera:camera-core:1.1.0-alpha11" implementation "androidx.camera:camera-camera2:1.1.0-alpha11" implementation "androidx.camera:camera-lifecycle:1.1.0-alpha11" implementation "androidx.camera:camera-view:1.0.0-alpha31" implementation "androidx.camera:camera-extensions:1.0.0-alpha31"}使用1.0.2版本的CameraX核心库会报错，找不到getOrCreateInstance方法。
??? bug "NoSuchMethodError getOrCreateInstance"
```logCrashHandler: In thread: Thread[main,5,main] UncaughtException detected: java.lang.NoSuchMethodError: No static method getOrCreateInstance(Landroid/content/Context;)Lcom/google/common/util/concurrent/ListenableFuture; in class Landroidx/camera/core/CameraX; or its super classes (declaration of 'androidx.camera.core.CameraX' appears in /data/app/com.rustfisher.tutorial2020-1/base.apk) at androidx.camera.lifecycle.ProcessCameraProvider.getInstance(ProcessCameraProvider.java:149) at com.rustfisher.tutorial2020.camera.SimplePreviewXAct.onCreate(SimplePreviewXAct.java:36) at android.app.Activity.performCreate(Activity.java:6161) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1112) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2507) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2640) at android.app.ActivityThread.access$800(ActivityThread.java:182) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1493) at android.os.Handler.dispatchMessage(Handler.java:111) at android.os.Looper.loop(Looper.java:194) at android.app.ActivityThread.main(ActivityThread.java:5682) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:963) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:758)```权限#
需要动态申请android.permission.CAMERA权限
<uses-permission android:name="android.permission.CAMERA" />本文略过动态申请权限的地方
界面#
CameraX为开发者贴心地准备了androidx.camera.view.PreviewView
把它放在一个FrameLayout里，如下的act_simple_preivew_x.layout
<?xml version="1.0" encoding="utf-8"?><layout> <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/container" android:layout_width="match_parent" android:layout_height="match_parent"> <androidx.camera.view.PreviewView android:id="@+id/previewView" android:layout_width="match_parent" android:layout_height="match_parent" /> </FrameLayout></layout>开启预览#
在activity中开启相机预览
// SimplePreviewXAct.javaimport android.os.Bundle;import androidx.annotation.NonNull;import androidx.annotation.Nullable;import androidx.appcompat.app.AppCompatActivity;import androidx.camera.core.Camera;import androidx.camera.core.CameraSelector;import androidx.camera.core.Preview;import androidx.camera.lifecycle.ProcessCameraProvider;import androidx.core.content.ContextCompat;import androidx.databinding.DataBindingUtil;import androidx.lifecycle.LifecycleOwner;import com.google.common.util.concurrent.ListenableFuture;// import com.rustfisher.tutorial2020.R;// import com.rustfisher.tutorial2020.databinding.ActSimplePreivewXBinding;import java.util.concurrent.ExecutionException;public class SimplePreviewXAct extends AppCompatActivity { private ActSimplePreivewXBinding mBinding; private ListenableFuture<ProcessCameraProvider> cameraProviderFuture; @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); mBinding = DataBindingUtil.setContentView(this, R.layout.act_simple_preivew_x); cameraProviderFuture = ProcessCameraProvider.getInstance(this); cameraProviderFuture.addListener(() -> { try { ProcessCameraProvider cameraProvider = cameraProviderFuture.get(); bindPreview(cameraProvider); } catch (ExecutionException | InterruptedException e) { // 这里不用处理 } }, ContextCompat.getMainExecutor(this)); } void bindPreview(@NonNull ProcessCameraProvider cameraProvider) { Preview preview = new Preview.Builder().build(); CameraSelector cameraSelector = new CameraSelector.Builder() .requireLensFacing(CameraSelector.LENS_FACING_BACK) .build(); preview.setSurfaceProvider(mBinding.previewView.getSurfaceProvider()); Camera camera = cameraProvider.bindToLifecycle(this, cameraSelector, preview); }}注意我们这里使用的是androidx.appcompat.app.AppCompatActivity
为了获得ProcessCameraProvider，用ProcessCameraProvider.getInstance方法拿到一个cameraProviderFuture。
在cameraProviderFuture完成后取出ProcessCameraProvider（cameraProvider）。
要开启预览，通过Preview.Builder构建一个Preview。用CameraSelector来选择后置摄像头。
Preview的SurfaceProvider由layout中的androidx.camera.view.PreviewView提供。
cameraProvider.bindToLifecycle绑定上后，启动摄像头预览
运行测试#
运行到手机上，打开这个Activity就可以看到摄像头预览。图像宽高比正常，没有拉伸现象。
- 荣耀 EMUI 3.1 Lite，Android 5.1 运行正常
- Redmi 9A，MIUI 12.5.1稳定版，Android 10 运行正常
- 一加5，H2OS 10.0.3，Android 10 运行正常
增加开关#
在layout里加2个按钮，控制相机开关
<?xml version="1.0" encoding="utf-8"?><layout> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical"> <LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:background="@color/colorPrimaryDark" android:gravity="center" android:orientation="horizontal" android:padding="4dp"> <Button android:id="@+id/start" style="@style/NormalBtn" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="打开" /> <Button android:id="@+id/end" style="@style/NormalBtn" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginStart="12dp" android:text="关闭" /> </LinearLayout> <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/container" android:layout_width="match_parent" android:layout_height="match_parent"> <androidx.camera.view.PreviewView android:id="@+id/previewView" android:layout_width="match_parent" android:layout_height="match_parent" /> </FrameLayout> </LinearLayout></layout>根layout换成LinearLayout
修改bindPreview方法，先检查传入的ProcessCameraProvider是否为空
private void bindPreview(ProcessCameraProvider cameraProvider) { if (cameraProvider == null) { Toast.makeText(getApplicationContext(), "没获取到相机", Toast.LENGTH_SHORT).show(); return; } Preview preview = new Preview.Builder().build(); CameraSelector cameraSelector = new CameraSelector.Builder() .requireLensFacing(CameraSelector.LENS_FACING_BACK) .build(); preview.setSurfaceProvider(mBinding.previewView.getSurfaceProvider()); Camera camera = cameraProvider.bindToLifecycle(this, cameraSelector, preview);}修改后的activity部分代码
import android.os.Bundle;import android.widget.Toast;import androidx.annotation.Nullable;import androidx.appcompat.app.AppCompatActivity;import androidx.camera.core.Camera;import androidx.camera.core.CameraSelector;import androidx.camera.core.Preview;import androidx.camera.lifecycle.ProcessCameraProvider;import androidx.core.content.ContextCompat;import androidx.databinding.DataBindingUtil;import com.google.common.util.concurrent.ListenableFuture;// import com.rustfisher.tutorial2020.R;// import com.rustfisher.tutorial2020.databinding.ActSimplePreivewXBinding;import java.util.concurrent.ExecutionException;public class SimplePreviewXAct extends AppCompatActivity { private ActSimplePreivewXBinding mBinding; private ListenableFuture<ProcessCameraProvider> mCameraProviderFuture; private ProcessCameraProvider mCameraProvider; private boolean mRunning = false; @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); mBinding = DataBindingUtil.setContentView(this, R.layout.act_simple_preivew_x); mCameraProviderFuture = ProcessCameraProvider.getInstance(this); mCameraProviderFuture.addListener(() -> { try { mCameraProvider = mCameraProviderFuture.get(); } catch (ExecutionException | InterruptedException e) { // 这里不用处理 } }, ContextCompat.getMainExecutor(this)); mBinding.start.setOnClickListener(v -> { if (mCameraProvider != null && !mRunning) { bindPreview(mCameraProvider); } }); mBinding.end.setOnClickListener(v -> { mCameraProvider.unbindAll(); mRunning = false; }); } private void bindPreview(ProcessCameraProvider cameraProvider) { if (cameraProvider == null) { Toast.makeText(getApplicationContext(), "没获取到相机", Toast.LENGTH_SHORT).show(); return; } Preview preview = new Preview.Builder().build(); CameraSelector cameraSelector = new CameraSelector.Builder() .requireLensFacing(CameraSelector.LENS_FACING_BACK) .build(); preview.setSurfaceProvider(mBinding.previewView.getSurfaceProvider()); Camera camera = cameraProvider.bindToLifecycle(this, cameraSelector, preview); mRunning = true; }}拿到mCameraProvider后不要立刻绑定生命周期。
如果要开启预览，则调用bindPreview(mCameraProvider)。记录一下现在相机已经开启预览mRunning = true。
如果要停止预览，则解绑生命周期mCameraProvider.unbindAll()。这个方法需要在主线程调用。
运行起来后，可以用按钮来控制相机预览的开关。相比之前，PreviewView的高度变小了一点（让了点位置给按钮）。
但视频宽高比例正常，没有被拉伸。默认的配置下，还有自动对焦的功能。
小结#
从简单的打开相机预览来看，CameraX简化了开发者的工作。提供了PreviewView，开发者不需要自定义SurfaceView或者TextureView。实时预览中，相机能够自动对焦。本文用的是1.1.0-alpha11，而CameraX还在发展之中。
参考#
- camerax实现预览 - developer.android.com
- https://developer.android.com/jetpack/androidx/releases/camera
- NoSuchMethodError - stackoverflow
原文链接CameraX 打开摄像头预览
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