问题

我正在使用Android Studio，使用Java编写代码。我试图编写一个软件，根据事件从摄像头拍摄照片。首先，我需要弄清楚API。Camera已经被弃用，所以有Camera2，但最新的是CameraX。我尝试过使用CameraX和Camera2，但出现了一个问题，我无法保存任何图像。我认为拍摄是成功的，但问题出在保存文件上。我不知道出了什么问题。

首先，让我们从权限开始。是的，我已经设置了相机和外部存储的权限。

<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

接下来，让我们看看代码本身。

我以前从未保存过照片，但我已经处理过文本文件，如.txt和.csv文件，我已经成功地使它们工作。

现在，我只需点击按钮来捕获图像，这不过是一个点击监听器。一旦我按下按钮，以下操作发生：

SimpleDateFormat mDateFormat = new SimpleDateFormat("yyyyMMddHHmmss", Locale.US);
File file = new File(Environment.getDataDirectory(), mDateFormat.format(new Date())+ ".jpg");

if(!file.exists())
    file.mkdirs();

ImageCapture.OutputFileOptions outputFileOptions = new ImageCapture.OutputFileOptions.Builder(file).build();
imageCapture.takePicture(outputFileOptions, executor, new ImageCapture.OnImageSavedCallback () {
    @Override
    public void onImageSaved(@NonNull ImageCapture.OutputFileResults outputFileResults) {
        Toast.makeText(MainActivity.this, "测试", Toast.LENGTH_SHORT).show();

        new Handler().post(new Runnable() {
            @Override
            public void run() {
                Toast.makeText(MainActivity.this, "图像保存成功", Toast.LENGTH_SHORT).show();
            }
        });
    }
    @Override
    public void onError(@NonNull ImageCaptureException error) {
        error.printStackTrace();
        //Toast.makeText(MainActivity.this, "图像保存失败！！！", Toast.LENGTH_SHORT).show();
    }
});

当应用程序首次启动时，它会请求权限，我授予权限。但是，当我按下捕获按钮时，查看Android Studio ID的运行选项卡，我会得到以下输出：

D/ImageCapture: 发送图像捕获请求 [current, pending] = [0, 1]
D/CaptureSession: 发出捕获请求。
W/example.camera: 线程[14,tid=10076,Runnable,Thread*=0xdc743000,peer=0x13184cf8,"Binder:10045_2"]上持有JNI关键锁21.148ms
W/ExifInterface: 由于错误的偏移可能导致无限循环，因此停止读取文件：0
    跳过标签条目，因为数据格式（ULONG）对于标签GPSAltitudeRef是意外的
W/ExifInterface: 由于错误的偏移可能导致无限循环，因此停止读取文件：0
    由于错误的偏移可能导致无限循环，因此停止读取文件：0
W/System.err: androidx.camera.core.ImageCaptureException: 无法写入或关闭文件
W/System.err:     at androidx.camera.core.ImageCapture$3.onError(ImageCapture.java:669)
        at androidx.camera.core.ImageSaver.lambda$postError$1$ImageSaver(ImageSaver.java:263)
        at androidx.camera.core.-$$Lambda$ImageSaver$eAp-cZyzsEk-LVLazzLE-ezQzwo.run(Unknown Source:8)
W/System.err:     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
        at java.lang.Thread.run(Thread.java:919)
    引起于：java.io.FileNotFoundException: /data/20200728142756.jpg: 打开失败：EACCES（权限被拒绝）
        at libcore.io.IoBridge.open(IoBridge.java:496)
        at java.io.FileOutputStream.<init>(FileOutputStream.java:235)
        at java.io.FileOutputStream.<init>(FileOutputStream.java:186)
        at androidx.camera.core.ImageSaver.run(ImageSaver.java:97)
    ... 3 more
W/System.err: 引起于：android.system.ErrnoException: 打开失败：EACCES（权限被拒绝）
        at libcore.io.Linux.open(Native Method)
        at libcore.io.ForwardingOs.open(ForwardingOs.java:167)
        at libcore.io.BlockGuardOs.open(BlockGuardOs.java:252)
        at libcore.io.ForwardingOs.open(ForwardingOs.java:167)
        at android.app.ActivityThread$AndroidOs.open(ActivityThread.java:7255)
        at libcore.io.IoBridge.open(IoBridge.java:482)
    ... 6 more
W/example.camera: 线程[16,tid=10083,Runnable,Thread*=0xdc74bc00,peer=0x13184de8,"Binder:10045_4"]上持有JNI关键锁17.651ms

我已经搜索过并尝试了不同的保存文件方法，当我使用Camera2 API并使用OutputStream保存文件时，似乎可以成功保存，但我不知道它保存在哪里。我之所以指出这一点，是因为我看到的是当我打开设备文件资源管理器时，它不允许我查看/storage/emulated/，只显示以下内容：

ls: /storage/emulated/: 权限被拒绝。

所有我找到的示例都假定可以轻松访问emulated。有没有人能提供关于为什么我会出现权限被拒绝错误的见解？

更新

所以，我仍然没有解决与失败的mkdir()调用相关的问题。但是，我解决了一个可能导致问题的问题。我创建目录和文件本身的方式不正确。

SimpleDateFormat mDateFormat = new SimpleDateFormat("yyyyMMddHHmmss", Locale.US);
File file = new File(getBatchDirectoryName(), mDateFormat.format(new Date())+ ".jpg");

public String getBatchDirectoryName() {

        String app_folder_path = "";
        app_folder_path = Environment.getExternalStorageDirectory() + "/images";
        File dir = new File(app_folder_path);
        if (!dir.exists

<details>
<summary>英文:</summary>

I&#39;m working with Android Studio, writing in Java. I&#39;m trying to write a piece of software that will take pictures from a camera based on an event. So first steps first was to figure out the API. Camera is depreciated, so there&#39;s Camera2, but the latest is CameraX. I&#39;ve attempted to use both CameraX and Camera2, but for some reason I&#39;m not saving any images. I believe the capture works, but the issue is saving the files. I don&#39;t know what&#39;s going on. 

First lets start with permissions. Yes, I have set permissions for both the camera and external storage. 

   
        &lt;uses-permission android:name=&quot;android.permission.CAMERA&quot; /&gt;
        &lt;uses-permission android:name=&quot;android.permission.WRITE_EXTERNAL_STORAGE&quot;/&gt;
        &lt;uses-permission android:name=&quot;android.permission.READ_EXTERNAL_STORAGE&quot;/&gt;
   
      
So lets move on to the code itself. 

I&#39;ve never saved photos before, but I have worked with text files such as .txt and .csv files. Which I&#39;ve been able to make work. 

Right now I do a simple button click to capture the image. Which is nothing more than an onclicklistener. Once I press the button this is what actions occur. 

                    SimpleDateFormat mDateFormat = new SimpleDateFormat(&quot;yyyyMMddHHmmss&quot;, Locale.US);
                    File file = new File(Environment.getDataDirectory(), mDateFormat.format(new Date())+ &quot;.jpg&quot;);
    
                    if(!file.exists())
                        file.mkdirs();
    
                    ImageCapture.OutputFileOptions outputFileOptions = new ImageCapture.OutputFileOptions.Builder(file).build();
                    imageCapture.takePicture(outputFileOptions, executor, new ImageCapture.OnImageSavedCallback () {
                        @Override
                        public void onImageSaved(@NonNull ImageCapture.OutputFileResults outputFileResults) {
                            Toast.makeText(MainActivity.this, &quot;TEST&quot;, Toast.LENGTH_SHORT).show();
    
                            new Handler().post(new Runnable() {
                                @Override
                                public void run() {
                                    Toast.makeText(MainActivity.this, &quot;Image Saved successfully&quot;, Toast.LENGTH_SHORT).show();
                                }
                            });
                        }
                        @Override
                        public void onError(@NonNull ImageCaptureException error) {
                            error.printStackTrace();
    //                        Toast.makeText(MainActivity.this, &quot;Image save FAILED!!!!&quot;, Toast.LENGTH_SHORT).show();
                        }
                    });



when the app launches the first time, it asks for permission and I grant permission. but looking at the run tab as part of the Android Studio ID, I get the following readout, when I press the capture button

    D/ImageCapture: Send image capture request [current, pending] = [0, 1]
    D/CaptureSession: Issuing capture request.
    W/example.camera: JNI critical lock held for 21.148ms on Thread[14,tid=10076,Runnable,Thread*=0xdc743000,peer=0x13184cf8,&quot;Binder:10045_2&quot;]
    W/ExifInterface: Stop reading file since a wrong offset may cause an infinite loop: 0
        Skip the tag entry since data format (ULONG) is unexpected for tag: GPSAltitudeRef
    W/ExifInterface: Stop reading file since a wrong offset may cause an infinite loop: 0
        Stop reading file since a wrong offset may cause an infinite loop: 0
    W/System.err: androidx.camera.core.ImageCaptureException: Failed to write or close the file
    W/System.err:     at androidx.camera.core.ImageCapture$3.onError(ImageCapture.java:669)
            at androidx.camera.core.ImageSaver.lambda$postError$1$ImageSaver(ImageSaver.java:263)
            at androidx.camera.core.-$$Lambda$ImageSaver$eAp-cZyzsEk-LVLazzLE-ezQzwo.run(Unknown Source:8)
    W/System.err:     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
            at java.lang.Thread.run(Thread.java:919)
        Caused by: java.io.FileNotFoundException: /data/20200728142756.jpg: open failed: EACCES (Permission denied)
            at libcore.io.IoBridge.open(IoBridge.java:496)
            at java.io.FileOutputStream.&lt;init&gt;(FileOutputStream.java:235)
            at java.io.FileOutputStream.&lt;init&gt;(FileOutputStream.java:186)
            at androidx.camera.core.ImageSaver.run(ImageSaver.java:97)
        	... 3 more
    W/System.err: Caused by: android.system.ErrnoException: open failed: EACCES (Permission denied)
            at libcore.io.Linux.open(Native Method)
            at libcore.io.ForwardingOs.open(ForwardingOs.java:167)
            at libcore.io.BlockGuardOs.open(BlockGuardOs.java:252)
            at libcore.io.ForwardingOs.open(ForwardingOs.java:167)
            at android.app.ActivityThread$AndroidOs.open(ActivityThread.java:7255)
            at libcore.io.IoBridge.open(IoBridge.java:482)
        	... 6 more
    W/example.camera: JNI critical lock held for 17.651ms on Thread[16,tid=10083,Runnable,Thread*=0xdc74bc00,peer=0x13184de8,&quot;Binder:10045_4&quot;]


I&#39;ve searched around, and looked for different methods of saving the file, and I&#39;ve had success with saving the image, sort of, when I use the camera2 api and save the file using outputstream

When I use Camera2 it appears to save just fine, but I have no idea where it saves, I can&#39;t find it. I point this out, because it still appears to be a permission denied error as what I&#39;m seeing is when I open up Device File Explorer its not letting me view /storage/emulator/ it just shows me 

    ls: /storage/emulated/: Permission denied. 

[![enter image description here][1]][1]


  [1]: https://i.stack.imgur.com/6PCyU.png

all the examples I have found have assumed access with no issues to emulated. 

Does anyone have any insight as to why I&#39;m having permission denied errors?

__________**UPDATE**__________

So I still haven&#39;t solved the issue related to the failed mkdir() call. However, I did fix one issue, that could have been causing the issue. The means as to how I was creating the directory and the file itself wasn&#39;t correct. 



    SimpleDateFormat mDateFormat = new SimpleDateFormat(&quot;yyyyMMddHHmmss&quot;, Locale.US);
    File file = new File(getBatchDirectoryName(), mDateFormat.format(new Date())+ &quot;.jpg&quot;);
    
    public String getBatchDirectoryName() {
    
            String app_folder_path = &quot;&quot;;
            app_folder_path = Environment.getExternalStorageDirectory() + &quot;/images&quot;;
            File dir = new File(app_folder_path);
            if (!dir.exists() &amp;&amp; !dir.mkdirs()) {
                Toast.makeText(MainActivity.this, &quot;Trip&quot;, Toast.LENGTH_SHORT).show();
            }
    
            return app_folder_path;
        }

However, it still fails to create the directory. Which still makes me come back to a permission issue. 

Environment.getExternalStorageDirectory() appears to be deprecated. Documentation appears to recommend using getExternalFilesDir(string) or MediaStore. However, I&#39;m having issues finding sample use cases. And I can&#39;t imagine, that while deprecated, it would just stop working at all. Most devices on the market are not API 29 or higher.  

</details>


# 答案1
**得分**: 2

基于 @blackapps 的帮助，我成功修改了我的清单文件以允许访问外部存储。

更多信息可以在这里找到：

[请求传统外部存储][1]

通过 @blackapps 和 stackoverflow 上的这个帖子，我成功更新了我的权限以允许传统访问。

因为在 Android Q 中，他们禁用了直接文件访问，他们添加了一个解决方法来支持传统访问。正如其他人已经提到的，这只是解决问题的临时方法。您将需要按照 Android R 的新格式保存文件。在我的情况下，我只是在开发一个概念验证，不需要担心 Android 的未来版本。

要进行临时修复，请执行以下操作

在您的清单文件的 <application> 标签内添加以下行

android:requestLegacyExternalStorage="true">

应该类似于这样
```xml
<?xml version="1.0" encoding="utf-8"?>
...
package="com.example.camerax">
...
<application
...
android:requestLegacyExternalStorage="true">
<activity android:name=".MainActivity">
<intent-filter>
...
</intent-filter>
</activity>
</application>
</manifest>

请记住，这不是长期解决方案，当设备升级到 Android R 时将无效。

android:requestLegacyExternalStorage="true">

    <?xml version="1.0" encoding="utf-8"?>
...
package="com.example.camerax">
...
<application
...
android:requestLegacyExternalStorage="true">
<activity android:name=".MainActivity">
<intent-filter>
...
</intent-filter>
</activity>
</application>