android - 某些安卓设备上的相机访问错误

Question

我写了一个利用手机相机的应用程序。 在我试过的大多数设备上它都运行良好，但有些应用程序在打开时崩溃。 稍微调试一下，发现访问摄像头时出现问题。

完整错误信息:

06-14 23:15:01.550 21872-21872/bguproject.vlc E/AndroidRuntime: FATAL EXCEPTION: main
Process: bguproject.vlc, PID: 21872
java.lang.RuntimeException: Unable to start activity ComponentInfo{bguproject.vlc/bguproject.vlc.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.hardware.Camera$Parameters android.hardware.Camera.getParameters()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2434)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2494)
at android.app.ActivityThread.access$900(ActivityThread.java:157)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1356)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5525)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.hardware.Camera$Parameters android.hardware.Camera.getParameters()' on a null object reference
at bguproject.vlc.MainActivity.onCreate(MainActivity.java:54)
at android.app.Activity.performCreate(Activity.java:6272)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2494) 
at android.app.ActivityThread.access$900(ActivityThread.java:157) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1356) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5525) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:730) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:620) 

如您所见，错误提示我尝试在空对象引用上调用虚拟方法，如果 mCamera 的写入正确完成，则不会发生这种情况

代码(写在末尾的try-catch语句上):

package bguproject.vlc;

import android.app.Activity;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.hardware.Camera;
import android.net.Uri;
import android.os.Bundle;
import android.os.SystemClock;
import android.view.View;
import android.widget.FrameLayout;
import android.widget.ScrollView;


public class MainActivity extends Activity implements View.OnClickListener{
    private Camera mCamera = null;
    private CameraView mCameraView = null;
    private int fpsRate[] = new int[2];
    private  boolean work = true,receiving = false;
    private boolean send = false;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Logger l = Logger.getInstance(this); //create the logger instance

        Logger.Log("Starting VLC app...");

        try{
            bguproject.vlc.Logger.Log("\tAccessing camera...");
            mCamera = Camera.open();//you can use open(int) to use different cameras
        } catch (Exception e){
            bguproject.vlc.Logger.LogError("\tFailed to get camera: " + e.getMessage());
        }

完整代码: http://pastebin.com/hxqJK3t2

所有被压碎的手机都有一个可用的摄像头并且相对较新(Samsung s6、samsung s7 和 LG g4)。

Answer 1

三星 S6 和 LG G4 都可以升级到 Android Marshmallow(v6 或 API 23)，而三星 S7 正在 stock ROM 上运行 Marshmallow，所以我假设所有 3 台设备都在运行 Marshmallow :)

From https://developer.android.com/training/permissions/requesting.html
Note: Beginning with Android 6.0 (API level 23), users can revoke permissions from any app at any time, even if the app targets a lower API level. You should test your app to verify that it behaves properly when it's missing a needed permission, regardless of what API level your app targets.

除了 list 中设置的权限外，您还需要在运行时请求/检查权限。您可以使用其中的示例代码，或者...

快速解决方案，

go to Settings-> Apps->(Your app name)->Permissions and enable the camera permission. Done, although not recommended for final product

然后再次尝试您的应用。现在应该可以工作了:D