surfaceView.getHolder未返回SurfaceHolder

Question

我正在尝试编写一个使用摄像头的应用程序。在尝试获取最终传递给启动相机的surfaceCreated()的surfaceHolder时，我得到了一个NullPointerException。是否存在getHolder()返回NULL的情况？

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

Answer 1

开始一个新的答案，希望更清楚。再一次，我认为根本问题是你在onCreate和onResume中做的东西的数量。

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您开始处理surfaceView和开始使用它之前运行它们的过程。

我不确定这一点，但以下是我在一个有效的增强现实应用程序中处理的各种相机和表面视图的各种地方的细目：

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 format, int w, int h)
{
    mCamera.setPreviewDisplay(holder);
    // set any cam params you need...

    mCamera.startPreview();
}

试着重构你的代码来做类似的事情。我的眼睛昏昏欲睡，试图从你的来源数出NPE发生在哪里，但我认为有几个问题：

在直接调用setContentView()

• youre调用
• 方法之前，您似乎要尝试获取对surfaceCreated的引用，而不是让它通过回调调用。

希望这能有所帮助。我们会弄清楚这件事的！

Answer 2

不经意间，我认为你需要用onResume而不是onCreate来做surfaceView的事情，否则它看起来还不错。

此外，您应该尝试呼叫：

mSurfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS); 
mSurfaceHolder.setSizeFromLayout();

就在你得到持有者的引用之后，但在开始预览之前。