java - 尝试在空对象引用上调用虚拟方法 'android.view.SurfaceHolder android.view.SurfaceView.getHolder()'

Question

我将使用 Camera 简单地生成录像机应用程序。但它崩溃了，给我一个吼叫错误:

Attempt to invoke virtual method 'android.view.SurfaceHolderandroid.view.SurfaceView.getHolder()' on a null object reference`

Capture Video Activity.class

import java.io.File;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;

import android.app.Activity;
import android.content.pm.ActivityInfo;
import android.hardware.Camera;
import android.hardware.camera2.CameraCharacteristics;
import android.media.CamcorderProfile;
import android.media.MediaRecorder;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.Surface;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ToggleButton;

import static android.provider.MediaStore.Files.FileColumns.MEDIA_TYPE_IMAGE;
import static android.provider.MediaStore.Files.FileColumns.MEDIA_TYPE_VIDEO;

    public class CaptureVideoActivity extends Activity implements SurfaceHolder.Callback {

        private MediaRecorder mMediaRecorder;
        private Camera mCamera;
        private SurfaceView mSurfaceView;
        private SurfaceHolder mHolder;
        private View mToggleButton;
        private boolean mInitSuccesful;
        CameraCharacteristics characteristics;

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_capture_video);

            // we shall take the video in landscape orientation
            setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);

            mSurfaceView = (SurfaceView) findViewById(R.id.surfaceView);
            mHolder = mSurfaceView.getHolder();
            mHolder.addCallback(this);
            mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);

            mToggleButton = (ToggleButton) findViewById(R.id.toggleRecordingButton);
            mToggleButton.setOnClickListener(new View.OnClickListener() {
                @Override
                // toggle video recording
                public void onClick(View v) {
                    if (((ToggleButton) v).isChecked()) {
                        mMediaRecorder.start();
                        try {
                            Thread.sleep(7 * 1000); // This will recode for 10 seconds, if you don't want then just remove it.
                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                        //finish();
                    } else {
                        mMediaRecorder.stop();
                        mMediaRecorder.reset();
                        try {
                            initRecorder(mHolder.getSurface());
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                }
            });
        }

        /* Init the MediaRecorder, the order the methods are called is vital to
         * its correct functioning */
        private void initRecorder(Surface surface) throws IOException {
            // It is very important to unlock the camera before doing setCamera
            // or it will results in a black preview
            if (mCamera == null) {
                mCamera = Camera.open();
                mCamera.unlock();
            }

            if (mMediaRecorder == null) mMediaRecorder = new MediaRecorder();
            mMediaRecorder.setPreviewDisplay(surface);
            mMediaRecorder.setCamera(mCamera);

            File file = getOutputMediaFile(2);
            mMediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
            mMediaRecorder.setVideoSource(MediaRecorder.VideoSource.SURFACE);
            //       mMediaRecorder.setOutputFormat(8);
           // mMediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.MPEG_4);
            mMediaRecorder.setOutputFile(file.getAbsolutePath());
            mMediaRecorder.setProfile(CamcorderProfile.get(CamcorderProfile.QUALITY_720P));
            /*mMediaRecorder.setVideoEncoder(MediaRecorder.VideoEncoder.H264);
            mMediaRecorder.setVideoEncodingBitRate(512 * 1000);
            mMediaRecorder.setVideoFrameRate(30);
            mMediaRecorder.setVideoSize(640, 480);*/
            int deviceorientation = getResources().getConfiguration().orientation;
            mMediaRecorder.setOrientationHint(getJpegOrientation(characteristics, deviceorientation));

            try {
                mMediaRecorder.prepare();
            } catch (IllegalStateException e) {
                // This is thrown if the previous calls are not called with the
                // proper order
                e.printStackTrace();
            }

            mInitSuccesful = true;
        }

        @Override
        public void surfaceCreated(SurfaceHolder holder) {
            try {
                if (!mInitSuccesful)
                    initRecorder(mHolder.getSurface());
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void surfaceDestroyed(SurfaceHolder holder) {
            shutdown();
        }

        @Override
        public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        }

        private void shutdown() {
            // Release MediaRecorder and especially the Camera as it's a shared
            // object that can be used by other applications
            mMediaRecorder.reset();
            mMediaRecorder.release();
            mCamera.release();

            // once the objects have been released they can't be reused
            mMediaRecorder = null;
            mCamera = null;
        }

        private static File getOutputMediaFile(int type){
            // To be safe, you should check that the SDCard is mounted
            // using Environment.getExternalStorageState() before doing this.

            File mediaStorageDir = new File(Environment.getExternalStoragePublicDirectory(
                    Environment.DIRECTORY_PICTURES), "Test Capture");
            // This location works best if you want the created images to be shared
            // between applications and persist after your app has been uninstalled.

            // Create the storage directory if it does not exist
            if (! mediaStorageDir.exists()){
                if (! mediaStorageDir.mkdirs()){
                    Log.d("MyCameraApp", "failed to create directory");
                    return null;
                }
            }

            // Create a media file name
            String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());
            File mediaFile;
            if (type == MEDIA_TYPE_IMAGE){
                mediaFile = new File(mediaStorageDir.getPath() + File.separator +
                        "IMG_"+ timeStamp + ".jpg");
            } else if(type == MEDIA_TYPE_VIDEO) {
                mediaFile = new File(mediaStorageDir.getPath() + File.separator +
                        "VID_"+ timeStamp + ".mp4");
            } else {
                return null;
            }

            return mediaFile;
        }

        private int getJpegOrientation(CameraCharacteristics c, int deviceOrientation) {
            if (deviceOrientation == android.view.OrientationEventListener.ORIENTATION_UNKNOWN)
                return 0;
            int sensorOrientation = c.get(CameraCharacteristics.SENSOR_ORIENTATION);

            // Round device orientation to a multiple of 90
            deviceOrientation = (deviceOrientation + 45) / 90 * 90;

            // Reverse device orientation for front-facing cameras
            boolean facingFront = c.get(CameraCharacteristics.LENS_FACING) == CameraCharacteristics.LENS_FACING_FRONT;
            if (facingFront) deviceOrientation = -deviceOrientation;

            // Calculate desired JPEG orientation relative to camera orientation to make
            // the image upright relative to the device orientation
            return (sensorOrientation + deviceOrientation + 360) % 360;

        }
    }

activity_capture_video.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <ToggleButton
        android:id="@+id/toggleRecordingButton"
        android:layout_width="fill_parent"
        android:textOff="Start Recording"
        android:textOn="Stop Recording"
        android:layout_height="wrap_content"
        />
    <FrameLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent">
        <SurfaceView android:id="@+id/surfaceView"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"></SurfaceView>

    </FrameLayout>
</LinearLayout>

我已经阅读了所有链接详细信息:

• How to solve "android.view.SurfaceView.getHolder()' on a null object reference"?

• 'android.view.SurfaceHolder android.view.SurfaceView.getHolder()' on a null object reference in SurfaceView

• surfaceView.getHolder not returning SurfaceHolder

但对我没有用。

Answer 1

我猜您正在关注一些教程视频或网站。如果没有，请立即执行。

检查以下内容。

1. 主要检查所有 surfaceview、surfaceholder 和 camera 的进口声明。
2. 检查xml中的元素。
3. 通过ctrl+点击R.id.surfaceView检查xml是否链接到java