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"

```log

CrashHandler: 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.java

import 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

原文链接CameraX 打开摄像头预览