最近在测试摄像头，所以需要产看摄像头获取的图像做预览

记录一下对应的代码，方便以后随时可以查看

布局代码

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <SurfaceView
        android:id="@+id/mdeia_camera__SurfaceView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:paddingBottom="50dp"
        ></SurfaceView>


    <Button
        android:id="@+id/mdeia_camera__btn_camera"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="5dp"
        android:layout_marginEnd="5dp"
        android:layout_weight="1"
        android:text="启动" />

</androidx.constraintlayout.widget.ConstraintLayout>

java代码

package com.example.aeke.Media;

import android.graphics.PixelFormat;
import android.hardware.Camera;
import android.os.Build;
import android.os.Bundle;
import android.view.Surface;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.widget.Button;

import com.example.aeke.R;

import java.io.IOException;

import androidx.annotation.Nullable;
import androidx.annotation.RequiresApi;
import androidx.appcompat.app.AppCompatActivity;

public class CameraText extends AppCompatActivity {

    private SurfaceView photoView;     // SurfaceView对象：(视图组件)视频显示
    private SurfaceHolder photoHolder; // SurfaceHolder对象：(抽象接口)SurfaceView支持类
    private Camera camera;         // Camera对象，相机预览

    private  Boolean isPreview =false;//是否预览状态

    Button btn;
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.media_camera);

        photoView = (SurfaceView)findViewById(R.id.mdeia_camera__SurfaceView);//用户显示摄像头预览的
        btn = (Button)findViewById(R.id.mdeia_camera__btn_camera);
        
        SurfaceHolder surfaceHolder = photoView.getHolder(); //用户显示
        surfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);//设置surfacView不维护缓冲
        
        btn.setOnClickListener(new View.OnClickListener() {
            @RequiresApi(api = Build.VERSION_CODES.FROYO)
            @Override
            public void onClick(View v) {

                if(!isPreview)
                {
                    camera =Camera.open();//打开摄像头
                    isPreview =true;
                }
                camera= Camera.open();
                try {
                    camera.setPreviewDisplay(surfaceHolder); //设置用户显示预览的SuffaceView
                    camera.setDisplayOrientation(270);
                    Camera.Parameters parameters =camera.getParameters();//获取摄像头参数
                    parameters.setPictureFormat(PixelFormat.JPEG);//设置图片为JPG图片
                    parameters.set("jpeg-quality",80);//设置图片质量

                    camera.setParameters(parameters);//设置摄像头参数
                    camera.startPreview();//开始预览
                    camera.autoFocus(null);//设置自动对焦

                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        });
    }
}

权限功能

    <!-- 相机功能 - 您的应用程序还必须声明使用相机功能-->
    <uses-permission android:name="android.permission.CAMERA" />

基本上加上去后，就可以了