我正在尝试编写使用相机的应用程序.在尝试获取我最终传递给启动摄像头的surfaceCreated()的surfaceHolder时,我得到一个NullPointerException. getHolder()返回NULL时有什么情况吗？
谢谢.
package com.tecmark; import java.io.IOException; import android.app.Activity; import android.graphics.PixelFormat; import android.hardware.Camera; import android.os.Bundle; import android.util.Log; import android.view.SurfaceHolder; import android.view.SurfaceView; import android.view.Window; import android.view.WindowManager; public class cameraview extends Activity implements SurfaceHolder.Callback{ SurfaceView mSurfaceView; SurfaceHolder mSurfaceHolder; Camera mCamera; boolean mPreviewRunning; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); getwindow().setFormat(PixelFormat.TRANSLUCENT); requestwindowFeature(Window.FEATURE_NO_TITLE); getwindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,WindowManager.LayoutParams.FLAG_FULLSCREEN); //setContentView(R.layout.camera_surface); mSurfaceView = (SurfaceView) findViewById(R.id.surface_camera); Log.i("surfaceholder = ","about to get surface holder"); try{ mSurfaceHolder = mSurfaceView.getHolder(); }catch(Exception e){ e.printstacktrace(); } Log.i("surfaceholder = ",""+mSurfaceHolder.toString()); mSurfaceHolder.addCallback(this); mSurfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS); setContentView(R.layout.camera_surface); surfaceCreated(mSurfaceHolder); } @Override public void surfaceChanged(SurfaceHolder holder,int format,int w,int h) { if (mPreviewRunning) { mCamera.stopPreview(); } Camera.Parameters p = mCamera.getParameters(); p.setPreviewSize(w,h); mCamera.setParameters(p); try { mCamera.setPreviewdisplay(holder); } catch (Exception e) { e.printstacktrace(); } mCamera.startPreview(); mPreviewRunning = true; } @Override public void surfaceCreated(SurfaceHolder holder) { try{ Log.i("camera ","about to open camera"); mCamera = Camera.open(); Log.i("camera "," camera opened"); mCamera.getParameters(); mCamera.setPreviewdisplay(holder); mCamera.startPreview(); } catch (IOException e) { e.printstacktrace(); } Log.i("camera ","ok"); } @Override public void surfaceDestroyed(SurfaceHolder holder) { mCamera.stopPreview(); mPreviewRunning = false; mCamera.release(); } }//end of activity 01-31 15:29:17.773: WARN/System.err(9144): java.lang.NullPointerException 01-31 15:29:17.778: WARN/System.err(9144): at com.tecmark.cameraview.onCreate(cameraview.java:42) 01-31 15:29:17.778: WARN/System.err(9144): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 01-31 15:29:17.778: WARN/System.err(9144): at android.app.ActivityThread.performlaunchActivity(ActivityThread.java:2459) 01-31 15:29:17.783: WARN/System.err(9144): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512) 01-31 15:29:17.783: WARN/System.err(9144): at android.app.ActivityThread.access$2200(ActivityThread.java:119) 01-31 15:29:17.783: WARN/System.err(9144): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863) 01-31 15:29:17.783: WARN/System.err(9144): at android.os.Handler.dispatchMessage(Handler.java:99) 01-31 15:29:17.783: WARN/System.err(9144): at android.os.Looper.loop(Looper.java:123) 01-31 15:29:17.783: WARN/System.err(9144): at android.app.ActivityThread.main(ActivityThread.java:4363) 01-31 15:29:17.783: WARN/System.err(9144): at java.lang.reflect.Method.invokeNative(Native Method) 01-31 15:29:17.788: WARN/System.err(9144): at java.lang.reflect.Method.invoke(Method.java:521) 01-31 15:29:17.788: WARN/System.err(9144): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) 01-31 15:29:17.788: WARN/System.err(9144): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 01-31 15:29:17.788: WARN/System.err(9144): at dalvik.system.NativeStart.main(Native Method) 01-31 15:29:17.793: DEBUG/AndroidRuntime(9144): Shutting down VM 01-31 15:29:17.793: WARN/dalvikvm(9144): threadid=3: thread exiting with uncaught exception (group=0x4001b180) 01-31 15:29:17.793: ERROR/AndroidRuntime(9144): Uncaught handler: thread main exiting due to uncaught exception 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.tecmark/com.tecmark.cameraview}: java.lang.NullPointerException 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): at android.app.ActivityThread.performlaunchActivity(ActivityThread.java:2496) 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512) 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): at android.app.ActivityThread.access$2200(ActivityThread.java:119) 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863) 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): at android.os.Handler.dispatchMessage(Handler.java:99) 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): at android.os.Looper.loop(Looper.java:123) 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): at android.app.ActivityThread.main(ActivityThread.java:4363) 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): at java.lang.reflect.Method.invokeNative(Native Method) 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): at java.lang.reflect.Method.invoke(Method.java:521) 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860) 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618) 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): at dalvik.system.NativeStart.main(Native Method) 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): Caused by: java.lang.NullPointerException 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): at com.tecmark.cameraview.onCreate(cameraview.java:47) 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): at android.app.ActivityThread.performlaunchActivity(ActivityThread.java:2459) 01-31 15:29:17.803: ERROR/AndroidRuntime(9144): ... 11 more
解决方法
开始一个新的答案,希望更清楚.同样,我认为根本问题是你在onCreate和onResume上做的事情的数量.
我认为您遇到的根本问题是视图/活动生命周期的某些部分需要在开始处理surfaceView并开始使用它之前运行它们的过程.
我不确定这一点,但是这里有各种各样的地方的故障,我在一个增强现实应用程序中处理各种相机和表面视图的东西：
onCreate()
{
// just set content view. do nothing with the camera or surfaceView yet
setContentView(R.layout.main);
}
onResume()
{
// open camera
mCamera = Camera.open();
// init surface view
sv = (SurfaceView)this.findViewById(R.id.SurfaceView01);
mHolder = sv.getHolder();
mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
mHolder.setSizefromLayout();
mHolder.addCallback(this);
}
surfaceChanged(SurfaceHolder holder,int h)
{
mCamera.setPreviewdisplay(holder);
// set any cam params you need...
mCamera.startPreview();
}
尝试重构代码以执行类似操作.我的眼睛变得闷闷不乐试图从你的来源算出NPE的发生地点,但我认为有一些问题是：
>你似乎试图在调用setContentView()之前尝试引用surfaceview
>你直接调用surfaceCreated方法,而不是让它通过回调调用.
希望有所帮助.我们还能解决这个问题！
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