Android CameraX 打开摄像头预览功能
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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
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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