怎样进行Android CameraX打开摄像头预览

怎样进行Android CameraX打开摄像头预览，相信很多没有经验的人对此束手无策，为此本文总结了问题出现的原因和解决方法，通过这篇文章希望你能解决这个问题。

前言

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

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

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 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

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 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。

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。

看完上述内容，你们掌握怎样进行Android CameraX打开摄像头预览的方法了吗？如果还想学到更多技能或想了解更多相关内容，欢迎关注行业资讯频道，感谢各位的阅读！