我是Android的编码新手（但不完全是Java），我正在尝试为Google Glass制作一个简单的相机应用程序。我希望它每隔几分钟自动拍摄一张照片并处理输入，但如果您使用本机Camera实现，Google Glass会强制您为每张照片“点击接受”。所以我正在尝试使用Android Camera API来拍照，这样我就可以跳过这个“点击接受”。
但是，在预览显示时，从不调用PictureCallback，因此在尝试将结果发送回主Activity时会抛出NullPointerException。
目前的代码是网上各种潜在解决方案的混乱，对不起，如果它太乱了！
我的相机活动课程：
package com.example.cerveau.blah;
import android.app.Activity;
import android.content.Intent;
import android.hardware.Camera;
import android.hardware.Camera.PictureCallback;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.widget.FrameLayout;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
public class CameraActivity extends Activity {
private Camera mCamera;
private CameraPreview mPreview;
private Intent resultIntent;
private PictureCallback mPicture;
public static final int MEDIA_TYPE_IMAGE = 1;
public static final int MEDIA_TYPE_VIDEO = 2;
private static final String TAG = "CameraActivity";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.recognize_places);
// Create an instance of Camera
mCamera = getCameraInstance();
// Make the callback
mPicture = new PictureCallback() {
private static final String TAG = "PictureCallback";
@Override
public void onPictureTaken(byte[] data, Camera camera) {
File pictureFile = getOutputMediaFile(MEDIA_TYPE_IMAGE);
if (pictureFile == null){
Log.d(TAG, "Error creating media file, check storage permissions: ");
return;
}
try {
FileOutputStream fos = new FileOutputStream(pictureFile);
fos.write(data);
fos.close();
} catch (FileNotFoundException e) {
Log.d(TAG, "File not found: " + e.getMessage());
} catch (IOException e) {
Log.d(TAG, "Error accessing file: " + e.getMessage());
}
Log.d(TAG, "Callback made and picture taken!");
}
};
// Create our Preview view and set it as the content of our activity.
mPreview = new CameraPreview(this, mCamera);
FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
preview.addView(mPreview);
Log.d(TAG, "Preview made!");
mCamera.startPreview();
// have a delay so the camera can set up
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
mCamera.takePicture(null, null, mPicture);
setIntent(getOutputMediaFileUri(MEDIA_TYPE_IMAGE));
releaseCamera();
}
public void setIntent(Uri photoURI){
resultIntent = new Intent();
resultIntent.setData(photoURI);
setResult(Activity.RESULT_OK, resultIntent);
finish();
}
public static Camera getCameraInstance(){
Camera c = null;
try {
c = Camera.open(); // attempt to get a Camera instance
}
catch (Exception e){
// Camera is not available (in use or does not exist)
}
// Parameters needed for Google Glass
c.setDisplayOrientation(0);
Camera.Parameters params = c.getParameters();
params.setPreviewFpsRange(30000, 30000);
params.setJpegQuality(90);
// hard-coding is bad, but I'm a bit lazy
params.setPictureSize(640, 480);
params.setPreviewSize(640, 480);
c.setParameters(params);
return c; // returns null if camera is unavailable
}
@Override
protected void onPause() {
super.onPause();
releaseCamera(); // release the camera immediately on pause event
}
private void releaseCamera(){
if (mCamera != null){
mCamera.release(); // release the camera for other applications
mCamera = null;
}
}
/** Create a file Uri for saving an image or video */
private static Uri getOutputMediaFileUri(int type){
return Uri.fromFile(getOutputMediaFile(type));
}
/** Create a File for saving an image or video */
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), "MyCameraApp");
// 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;
}
}
我在主Activity中称它为：
Intent intent = new Intent(this, CameraActivity.class);
startActivityForResult(intent, CAPTURE_IMAGE_ACTIVITY_REQUEST_CODE);
我的AndroidManifest中已经拥有所有必需的权限：
<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="com.google.android.glass.permission.DEVELOPMENT" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-feature android:name="android.hardware.camera" android:required="true"/>
这是错误日志：
10-30 18:00:58.599 11361-11361/com.example.cerveau.recognizeplaces D/OpenGLRenderer﹕ Enabling debug mode 0
10-30 18:00:58.833 11361-11361/com.example.cerveau.recognizeplaces D/CameraActivity﹕ Preview made!
10-30 18:01:08.654 11361-11361/com.example.cerveau.recognizeplaces I/Choreographer﹕ Skipped 601 frames! The application may be doing too much work on its main thread.
10-30 18:01:08.677 11361-11361/com.example.cerveau.recognizeplaces I/RecogPlaces﹕ Got to onActivity
10-30 18:01:08.677 11361-11361/com.example.cerveau.recognizeplaces I/RecogPlaces﹕ Request code: 100, Result code: -1, what it wants: -1
10-30 18:01:08.677 11361-11361/com.example.cerveau.recognizeplaces I/RecogPlaces﹕ Got inside the IF
10-30 18:01:08.685 11361-11361/com.example.cerveau.recognizeplaces D/AndroidRuntime﹕ Shutting down VM
10-30 18:01:08.685 11361-11361/com.example.cerveau.recognizeplaces W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x41600bd8)
10-30 18:01:08.685 11361-11361/com.example.cerveau.recognizeplaces E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.example.cerveau.recognizeplaces, PID: 11361
java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=100, result=-1, data=Intent { dat=file:///storage/emulated/0/Pictures/MyCameraApp/IMG_20141030_180059.jpg }} to activity {com.example.cerveau.recognizeplaces/com.example.cerveau.recognizeplaces.LiveCardMenuActivity}: java.lang.NullPointerException
at android.app.ActivityThread.deliverResults(ActivityThread.java:3391)
at android.app.ActivityThread.handleSendResult(ActivityThread.java:3434)
at android.app.ActivityThread.access$1300(ActivityThread.java:138)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1284)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:149)
at android.app.ActivityThread.main(ActivityThread.java:5045)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:602)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at java.io.File.fixSlashes(File.java:185)
at java.io.File.<init>(File.java:134)
at com.example.cerveau.recognizeplaces.LiveCardMenuActivity.processPictureWhenReady(LiveCardMenuActivity.java:166)
at com.example.cerveau.recognizeplaces.LiveCardMenuActivity.onActivityResult(LiveCardMenuActivity.java:157)
at android.app.Activity.dispatchActivityResult(Activity.java:5430)
at android.app.ActivityThread.deliverResults(ActivityThread.java:3387)
at android.app.ActivityThread.handleSendResult(ActivityThread.java:3434)
at android.app.ActivityThread.access$1300(ActivityThread.java:138)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1284)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:149)
at android.app.ActivityThread.main(ActivityThread.java:5045)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:602)
at dalvik.system.NativeStart.main(Native Method)
10-30 18:01:09.130 11361-11361/com.example.cerveau.recognizeplaces I/Process﹕ Sending signal. PID: 11361 SIG: 9
提前致谢！
答案 0 :(得分：0)
来自processPictureWhenReady()课程的LiveCardMenuActivity方法做错了。
首先，这是一件非常糟糕的事情：
Thread.sleep(1000);
永远不要在UI线程上执行此操作 你应该直接打电话
mCamera.startPreview();
mCamera.takePicture(null, null, mPicture);
在onPictureTaken()回调结束时：
setIntent(pictureFile.getPath());