Android 6 camera.open()异常解决方法_cannot open camera "0" without camera permission

最近需要在Android平台写一个处理视频帧的Demo，于是在网上下了很多的Demo代码，奇怪的是下载的很多通过Camera提取视频帧的程序在Android Studio中都能通过编译，但是每次一放到真机上一测试程序就闪退崩掉了。 
我的开发环境为Android Studio 2.1，编译时的SDK选的是API 23，测试机为华为P9。

网上搜了很多资料说要在AndroidManifest文件中添加访问Camera的权限，然而我添加之后依然没有解决。这个问题折腾了我快一周，后面我才发现是权限的问题。我的测试机华为P9是Android 6的系统，而Android系统从6.0版本开始增加了一种运行时权限，Camera正好属于运行时权限，这种权限的授权不像6.0以前的Android系统可以安装APP的时候就一次性授权。综上，最后找到了程序在华为P9上一测试就崩掉的原因：程序在运行中请求camera.open()时实际上程序并未获得操作Camera的权限，所以camera.open()会一直打开失败。

问题找到了，怎么解决呐？下面介绍方法有两种。

方法一：修改编译的SDK，在src下的build.gradle中把编译的SDK改为低于23版本的SDK（因为Android 6系统对应的最低SDK版本号为API level 23）。下面是一个示例。

<code class="hljs rust has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">apply plugin: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'com.android.application'</span>

android {
    compileSdkVersion <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22</span>
    buildToolsVersion <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"22.0.1"</span>

    defaultConfig {
        applicationId <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"org.mogujie.guigu.camerademo"</span>
        minSdkVersion <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">16</span>
        targetSdkVersion <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22</span>
        versionCode <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>
        versionName <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"1.0"</span>
    }
    buildTypes {
        release {
            minifyEnabled <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">false</span>
            proguardFiles getDefaultProguardFile(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'proguard-android.txt'</span>), <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'proguard-rules.pro'</span>
        }
    }
}

dependencies {
    compile fileTree(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">dir</span>: <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'libs'</span>, include: [<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'*.jar'</span>])
    testCompile <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'junit:junit:4.12'</span>
    compile <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">'com.android.support:appcompat-v7:22.0.0'</span>
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li></ul>

方法二：在Java代码中添加运行时权限授权。方法：在需要用Camera的地方添加授权代码，如在Mainactivity的onCreate函数中添加如下代码。

<code class="hljs javascript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">  <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// check Android 6 permission</span>
        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (ContextCompat.checkSelfPermission(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>, Manifest.permission.CAMERA)
                == PackageManager.PERMISSION_GRANTED) {
            Log.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"TEST"</span>,<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Granted"</span>);
            <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//init(barcodeScannerView, getIntent(), null);</span>
        } <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> {
            ActivityCompat.requestPermissions(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">this</span>,
                    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">String</span>[]{Manifest.permission.CAMERA}, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//1 can be another integer</span>
        }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

除此，由于以上代码来自其它包，因此还需要import下面的这些包

<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">import android<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Manifest</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
import android<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.app</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Activity</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
import android<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.content</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Intent</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
import android<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.content</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.pm</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.PackageManager</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
import android<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.os</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Bundle</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
import android<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.support</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.annotation</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.NonNull</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
import android<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.support</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.v</span>4<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.app</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ActivityCompat</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
import android<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.support</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.v</span>4<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.app</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.FragmentActivity</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
import android<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.support</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.v</span>4<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.content</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.ContextCompat</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
import android<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.view</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.KeyEvent</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

Reference： 
http://www.open-open.com/lib/view/open1450578678148.html 
https://github.com/open-keychain/open-keychain/blob/master/OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/QrCodeCaptureActivity.java