surfaceView.getHolder 不返回 SurfaceHolder

我正在尝试编写一个使用相机的应用程序。当尝试获取最终传递给启动相机的 surfaceCreated() 的 surfaceHolder 时，我收到 NullPointerException 。 getHolder()是否有返回NULL的情况？

thanks.

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

开始一个新的答案希望更清楚。再说一次，我认为根本问题是你在 onCreate 和 onResume 中所做的事情的数量。

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您开始处理 SurfaceView 并开始使用它之前运行它们的过程。

我不确定这一点，但这里是我在一个有效的增强现实应用程序中处理各种相机和表面视图内容的各个地方的细分：

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();
}

尝试重构您的代码以执行类似的操作。我的眼睛变得模糊，试图从你的来源中找出 NPE 发生的位置，但我认为有几个问题：

• 您似乎试图在调用 setContentView() 之前获取对 SurfaceView 的引用
• 您直接调用 surfaceCreated 方法，而不是通过回调调用它。

希望有帮助。我们会弄清楚这个问题的！