Mobile VisionbarcodeScanner：SurfaceView为啥不更新CameraSource？
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【中文标题】Mobile VisionbarcodeScanner：SurfaceView为啥不更新CameraSource？【英文标题】：Mobile Vision barcodeScanner: Why does SurfaceView not update CameraSource?Mobile VisionbarcodeScanner：SurfaceView为什么不更新CameraSource？ 【发布时间】：2017-05-08 20:02:58 【问题描述】：我一直在关注以下tutorial，它使用移动视觉 api 创建条形码/二维码扫描仪。虽然我已经输入了它所说的确切代码（至少我认为），但摄像头来自cameraSource。
我在这个过程中添加了一些额外的代码，看看它是否会有所作为，但它仍然没有。问题是当我启动应用程序时，SurfaceView 应该显示CAMERA_FACING_BACK 提要，但它是纯黑色的。如果您能告诉我为什么提要没有显示，如果有任何需要更改的代码，将不胜感激。
MainActivity.java：
package com.example.neekondev.barcodeshortened;
import android.Manifest;
import android.content.pm.PackageManager;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.util.SparseArray;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.widget.TextView;
import com.google.android.gms.vision.CameraSource;
import com.google.android.gms.vision.Detector;
import com.google.android.gms.vision.barcode.Barcode;
import com.google.android.gms.vision.barcode.BarcodeDetector;
import java.io.IOException;
import static com.google.android.gms.vision.CameraSource.CAMERA_FACING_BACK;
import static com.google.android.gms.vision.CameraSource.CAMERA_FACING_FRONT;
public class MainActivity extends AppCompatActivity
SurfaceView cameraView;
TextView barcodeInfo;
BarcodeDetector barcodeDetector;
CameraSource cameraSource;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
cameraView = (SurfaceView) findViewById(R.id.camera_view);
barcodeInfo = (TextView) findViewById(R.id.code_info);
barcodeDetector =
new BarcodeDetector.Builder(this)
.setBarcodeFormats(Barcode.CODE_39 | Barcode.CODE_93 | Barcode.CODE_128)
.build();
cameraSource = new CameraSource
.Builder(this, barcodeDetector)
.setRequestedPreviewSize(640, 480)
.setRequestedFps(20.0f)
.setFacing(CAMERA_FACING_BACK)
.build();
cameraView.getHolder().addCallback(new SurfaceHolder.Callback()
@Override
public void surfaceCreated(SurfaceHolder holder)
try
if (ActivityCompat.checkSelfPermission(getApplicationContext(),
Manifest.permission.CAMERA) !=
PackageManager.PERMISSION_GRANTED)
// TODO: Consider calling
// ActivityCompat#requestPermissions
// here to request the missing permissions, and then overriding
// public void onRequestPermissionsResult(int requestCode, String[] permissions,
// int[] grantResults)
// to handle the case where the user grants the permission. See the documentation
// for ActivityCompat#requestPermissions for more details.
return;
cameraSource.start(cameraView.getHolder());
catch (IOException ie)
Log.e("CAMERA SOURCE", ie.getMessage());
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height)
@Override
public void surfaceDestroyed(SurfaceHolder holder)
cameraSource.stop();
);
barcodeDetector.setProcessor(new Detector.Processor<Barcode>()
@Override
public void release()
@Override
public void receiveDetections(Detector.Detections<Barcode> detections)
final SparseArray<Barcode> barcodes = detections.getDetectedItems();
if (barcodes.size() != 0)
barcodeInfo.post(new Runnable() // Use the post method of the TextView
public void run()
barcodeInfo.setText( // Update the TextView
barcodes.valueAt(0).displayValue
);
);
);
activity_main.xml：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/activity_main"
android:layout_
android:layout_
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.neekondev.barcodeshortened.MainActivity">
<SurfaceView
android:layout_
android:layout_
android:layout_centerVertical="true"
android:layout_alignParentLeft="true"
android:id="@+id/camera_view"
/>
<TextView
android:layout_
android:layout_
android:id="@+id/code_info"
android:layout_toRightOf="@+id/camera_view"
android:textSize="20sp"
android:layout_marginLeft="16dp"
android:text="Nothing yet..."
android:layout_alignParentTop="true"
/>
</RelativeLayout>
manifest.xml：
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.neekondev.barcodeshortened">
<meta-data android:name="com.google.android.gms.vision.DEPENDENCIES" android:value="barcode"/>
<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.Camera"/>
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:supportsRtl="true"
android:theme="@style/AppTheme">
<activity android:name=".MainActivity">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
【问题讨论】：
【参考方案1】：没关系，我自己解决了这个问题，虽然我认为其他人在教程结束后可能会问同样的问题，所以我会告诉你哪里出了问题。您看，虽然我在 Manifest 中声明了权限，但 android.permissions.CAMERA 是“高风险权限”，这意味着用户需要手动同意才能实施。因为我从来没有直接向用户请求权限对话框，所以无法执行所有使用相机权限的代码，从而给我们提供了空白屏幕与相机的提要。一个简单的解决方法是进入设置并允许那里的权限，但可以使用以下代码代替，方便地通过对话框请求相机权限；
import android.Manifest;
import android.content.Intent;
import android.content.pm.ActivityInfo;
import android.content.pm.PackageManager;
import android.hardware.Camera;
import android.media.Image;
import android.os.Bundle;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.util.SparseArray;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.widget.RelativeLayout;
import android.widget.TextView;
import com.google.android.gms.vision.CameraSource;
import com.google.android.gms.vision.Detector;
import com.google.android.gms.vision.barcode.Barcode;
import com.google.android.gms.vision.barcode.BarcodeDetector;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import java.io.IOException;
import java.text.DateFormat;
import java.util.ArrayList;
import java.util.Date;
import static junit.framework.Assert.assertNotNull;
public class MainActivity
extends AppCompatActivity
FirebaseDatabase database;
DatabaseReference myRef;
SurfaceView cameraView;
TextView barcodeInfo;
BarcodeDetector barcodeDetector;
CameraSource cameraSource;
private static final int CAMERA_PERMISSION_CAMERA = 0x000000;
public static boolean position = false;
//Camera cam;
//Camera.Parameters p;
@Override
protected void onCreate(Bundle savedInstanceState)
setRequestedOrientation(ActivityInfo
.SCREEN_ORIENTATION_PORTRAIT);
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (ContextCompat.checkSelfPermission(MainActivity
.this,
Manifest
.permission
.CAMERA)
!= PackageManager
.PERMISSION_GRANTED)
// Should we show an explanation?
if (ActivityCompat.shouldShowRequestPermissionRationale(MainActivity
.this,
Manifest
.permission
.CAMERA))
// Show an explanation to the user *asynchronously* -- don't block
// this thread waiting for the user's response! After the user
// sees the explanation, try again to request the permission.
else
// No explanation needed, we can request the permission.
ActivityCompat.requestPermissions(MainActivity
.this,
new String[]Manifest.permission
.CAMERA,
CAMERA_PERMISSION_CAMERA);
// CAMERA_PERMISSION_CAMERA is an
// app-defined int constant. The callback method gets the
// result of the request.
cameraView = (SurfaceView) findViewById(R
.id
.camera_view);
barcodeInfo = (TextView) findViewById(R
.id
.code_info);
MainActivity
.this
.getPackageManager()
.hasSystemFeature
(PackageManager
.FEATURE_CAMERA_FLASH);
barcodeDetector =
new BarcodeDetector.Builder(getApplicationContext())
.setBarcodeFormats(Barcode.ALL_FORMATS)
.build();
cameraSource = new CameraSource
.Builder(getApplicationContext(), barcodeDetector)
.setFacing(CameraSource.CAMERA_FACING_BACK)
.setRequestedFps(35.0f)
.setRequestedPreviewSize(960, 960)
.setAutoFocusEnabled(true)
.build();
//setupButtons();
cameraView.getHolder().addCallback(new SurfaceHolder
.Callback()
@Override
public void surfaceCreated(SurfaceHolder holder)
try
if (ActivityCompat.checkSelfPermission(MainActivity.this,
Manifest.permission.CAMERA)
!= PackageManager.PERMISSION_GRANTED)
// TODO: CONSIDER CALLING
//ActivityCompat#requestPermissions
// here to request the missing permissions, and then overriding
// public void onRequestPermissionsResult(int requestCode, String[] permissions,
// int[] grantResults)
// to handle the case where the user grants the permission. See the documentation
// for ActivityCompat#requestPermissions for more details.
return;
cameraSource.start(cameraView
.getHolder());
catch (IOException ie)
Log.e("CAMERA SOURCE", ie
.getMessage());
@Override
public void surfaceChanged(SurfaceHolder holder,
int format,
int width,
int height)
@Override
public void surfaceDestroyed(SurfaceHolder holder)
cameraSource.stop();
);
barcodeDetector.setProcessor(new Detector.Processor<Barcode>()
@Override
public void release()
@Override
public void receiveDetections(Detector.Detections<Barcode> detections)
final SparseArray<Barcode> barcodes = detections.getDetectedItems();
database = FirebaseDatabase.getInstance();
myRef = database
.getReference(getTime());
if (barcodes
.size() != 0)
barcodeInfo
.post(new Runnable() // Use the post method of the TextView
public void run()
barcodeInfo.setText(barcodes
.valueAt(0)
.displayValue
);
myRef.setValue(barcodes
.valueAt(0)
.displayValue
);
);
);
/*
public void FLASH_ON()
cam = Camera.open();
p = cam.getParameters();
p.setFlashMode(Camera
.Parameters
.FLASH_MODE_TORCH);
cam.setParameters(p);
cam.startPreview();
public void FLASH_OFF()
cam.stopPreview();
cam.release();
public void setupButtons()
ImageButton flash = (ImageButton)findViewById(R.id.flash);
flash.setOnClickListener(new View.OnClickListener()
@Override
public void onClick(View v)
if (position == false)
FLASH_ON();
position = true;
if (position == true)
FLASH_OFF();
position = false;
);
*/
public String getTime()
String downToSeconds = DateFormat
.getDateTimeInstance()
.format(
new Date());
return downToSeconds;
@Override
public void onRequestPermissionsResult(int requestCode,
String permissions[],
int[] grantResults)
switch (requestCode)
case CAMERA_PERMISSION_CAMERA:
// If request is cancelled, the result arrays are empty.
if (grantResults.length > 0
&& grantResults[0]
== PackageManager
.PERMISSION_GRANTED)
Intent startMain = new Intent(MainActivity
.this, MainActivity
.class);
startActivity(startMain);
else
if (ContextCompat.checkSelfPermission(MainActivity
.this,
Manifest
.permission
.CAMERA)
!= PackageManager
.PERMISSION_GRANTED)
// Should we show an explanation?
if (ActivityCompat.shouldShowRequestPermissionRationale(MainActivity
.this,
Manifest
.permission
.CAMERA))
// Show an explanation to the user *asynchronously* -- don't block
// this thread waiting for the user's response! After the user
// sees the explanation, try again to request the permission.
else
// No explanation needed, we can request the permission.
ActivityCompat.requestPermissions(MainActivity
.this,
new String[]Manifest.permission
.CAMERA,
CAMERA_PERMISSION_CAMERA);
// CAMERA_PERMISSION_CAMERA is an
// app-defined int constant. The callback method gets the
// result of the request.
return;
请原谅我的一些服务器代码。我也在将结果上传到 firebase 数据库。其余的都是相同的。布局对缩放有一些小的调整，但其余部分是相同的。祝你好运！
【讨论】：
当用户允许权限时，您是否重新启动全部活动？ @androidnoobdev 是的，activity重启了。 需要重启activity才能触发surfaceCreated(SurfaceHolder holder)。以上是关于Mobile VisionbarcodeScanner：SurfaceView为啥不更新CameraSource？的主要内容，如果未能解决你的问题，请参考以下文章
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