我通过 SurfaceView 使用内部摄像头。但是当我按下主页按钮并重新启动时出现问题。我发现很多类似的问题。我尝试了很多方法，但他们无法修复。也许我错过了什么，所以请帮助我。谢谢我尝试下面无法修复 NullPointerException 的方法 1. 线程方法（它不起作用）
LogCat 表演
D / AndroidRuntime（571）：关闭VM
W / dalvikvm（571）：threadid = 1：线程退出未捕获的异常（组= 0x409961f8）
E / AndroidRuntime（571）：致命异常：主要
E / AndroidRuntime（571）：java .lang.NullPointerException
E/AndroidRuntime(571): 在 com.exampl.cameraexample.Preview.surfaceCreated(Preview.java:56)
E/AndroidRuntime(571): 在 android.view.SurfaceView.updateWindow(SurfaceView.java:562)
E/AndroidRuntime(571): 在 android.view.SurfaceView.access$000(SurfaceView.java:82)
E/AndroidRuntime(571): 在 android.view.SurfaceView$3.onPreDraw(SurfaceView.java:171)
E/AndroidRuntime( 571）：在 android.view.ViewTreeObserver.dispatchOnPreDraw（ViewTreeObserver.java:590）
E/AndroidRuntime(571)：在 android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1596)
E/AndroidRuntime(571)：在 android.view.ViewRootImpl.handleMessage(ViewRootImpl.java:2418)
E/AndroidRuntime(571) : 在 android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime(571): 在 android.os.Looper.loop(Looper.java:137)
E/AndroidRuntime(571): 在 android.app。 ActivityThread.main(ActivityThread.java:4340)
E/AndroidRuntime(571): 在 java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(571): 在 java.lang.reflect.Method.invoke(Method .java:511)
E/AndroidRuntime(571)：在 com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) E/AndroidRuntime(571)：在 com.android.internal.os.ZygoteInit.main(ZygoteInit. java:551)
E/AndroidRuntime(571): 在 dalvik.system.NativeStart.main(Native Method)
这是主要活动
package com.example.cameraexample;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.sql.Date;
import java.text.SimpleDateFormat;
import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.res.Configuration;
import android.hardware.Camera;
import android.hardware.Camera.PictureCallback;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.FrameLayout;
import android.widget.Toast;
public class MainActivity extends Activity {
private static final String TAG = "CameraDemo";
public static final int MEDIA_TYPE_IMAGE = 1;
public static final int MEDIA_TYPE_VIDEO = 2;
private Camera mCamera;
private Preview mPreview;
//Button captureButton;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
setRequestedOrientation(1);
//if (checkCameraHardware(this)) {
// Create an instance of Camera
//mCamera = getCameraInstance();
// }
// Create our Preview view and set it as the content of our activity.
// mPreview = new Preview(this, mCamera);
// FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
// preview.addView(mPreview);
// Add a listener to the Capture button
Button captureButton = (Button) findViewById(R.id.button_capture);
captureButton.setOnClickListener(
new View.OnClickListener() {
@Override
public void onClick(View v) {
// get an image from the camera
mCamera.takePicture(null, null, mPicture);
}
}
);
Log.d(TAG, "onCreate");
}
@Override
public void onConfigurationChanged(Configuration newConfig) {
// TODO Auto-generated method stub
super.onConfigurationChanged(newConfig);
Log.d(TAG, "onConfigurationChanged");
}
/** A safe way to get an instance of the Camera object. */
public static Camera getCameraInstance(){
Camera c = null;
try {
c = Camera.open(); // attempt to get a Camera instance
Log.d(TAG, "OPEN Camera!!!");
}
catch (Exception e){
// Camera is not available (in use or does not exist)
Log.d(TAG, "NULL Camera");
}
Log.d(TAG, "OPEN Camera");
return c; // returns null if camera is unavailable
}
PictureCallback mPicture = new 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());
}
mCamera.startPreview();
Log.d(TAG, "onPictureTaken");
}
};
/** Create a File for saving an image or video */
@SuppressLint("SimpleDateFormat")
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(type));
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;
}
@Override
protected void onDestroy() {
// TODO Auto-generated method stub
super.onDestroy();
Toast.makeText(this, "onDestroy", Toast.LENGTH_LONG).show();
Log.d(TAG, "onDestroy");
}
@Override
protected void onPause() {
super.onPause();
Toast.makeText(this, "onPause", Toast.LENGTH_LONG).show();
releaseCamera(); // release the camera immediately on pause event
Log.d(TAG, "onPause");
}
@Override
protected void onRestart() {
// TODO Auto-generated method stub
super.onRestart();
Toast.makeText(this, "onRestart", Toast.LENGTH_LONG).show();
Log.d(TAG, "onRestart");
}
@Override
protected void onResume() {
// TODO Auto-generated method stub
super.onResume();
//if (checkCameraHardware(this)) {
// Create an instance of Camera
mCamera = getCameraInstance();
// }
// Create our Preview view and set it as the content of our activity.
mPreview = new Preview(this, mCamera);
FrameLayout preview = (FrameLayout) findViewById(R.id.camera_preview);
preview.addView(mPreview);
Toast.makeText(this, "onResume", Toast.LENGTH_LONG).show();
Log.d(TAG, "onResume");
}
@Override
protected void onStart() {
// TODO Auto-generated method stub
super.onStart();
Toast.makeText(this, "onStart", Toast.LENGTH_LONG).show();
Log.d(TAG, "onStart");
}
@Override
protected void onStop() {
// TODO Auto-generated method stub
super.onStop();
Toast.makeText(this, "onStop", Toast.LENGTH_LONG).show();
Log.d(TAG, "onStop");
}
private void releaseCamera(){
if (mCamera != null){
mCamera.release(); // release the camera for other applications
mCamera = null;
}
}
}
另一个preview.java
package com.example.cameraexample;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.hardware.Camera;
import android.hardware.Camera.PreviewCallback;
import android.os.Handler;
import android.os.Message;
import android.util.Log;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.widget.Toast;
public class Preview extends SurfaceView implements SurfaceHolder.Callback, Runnable {
private static final String TAG = "Preview";
private Thread thread;
private boolean running;
private SurfaceHolder mHolder;
private Camera mCamera;
@SuppressWarnings("deprecation")
public Preview(Context context, Camera camera) {
super(context);
mCamera = camera;
if(camera==null){
Log.e("Camera","my camera is null...");
}
// Install a SurfaceHolder.Callback so we get notified when the
// underlying surface is created and destroyed.
mHolder = getHolder();
mHolder.addCallback(this);
// deprecated setting, but required on Android versions prior to 3.0
mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
Log.d(TAG, "Preview");
}
public void surfaceCreated(SurfaceHolder holder) {
// The Surface has been created, now tell the camera where to draw the preview.
try {
Log.d(TAG, "surfaceCreated STARTED");
running = true;
thread = new Thread(this, "himi_Thread_one");
thread.start();
mCamera.setPreviewDisplay(holder);
mCamera.setDisplayOrientation(90);
mCamera.startPreview();
} catch (IOException e) {
Log.d(TAG, "Error setting camera preview: " + e.getMessage());
}
Log.d(TAG, "surfaceCreated");
}
public void surfaceDestroyed(SurfaceHolder holder) {
// empty. Take care of releasing the Camera preview in your activity.
running = false;
Log.d(TAG, "surfaceDestroyed");
}
public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
// If your preview can change or rotate, take care of those events here.
// Make sure to stop the preview before resizing or reformatting it.
if (mHolder.getSurface() == null){
// preview surface does not exist
return;
}
// stop preview before making changes
try {
mCamera.stopPreview();
} catch (Exception e){
// ignore: tried to stop a non-existent preview
}
// set preview size and make any resize, rotate or
// reformatting changes here
// start preview with new settings
try {
mCamera.setPreviewDisplay(mHolder);
mCamera.setDisplayOrientation(90);
mCamera.startPreview();
} catch (Exception e){
Log.d(TAG, "Error starting camera preview: " + e.getMessage());
}
Log.d(TAG, "surfaceChanged");
}
public void run() {
while (running) {
try {
Thread.sleep(100);
} catch (Exception ex) {
}
}
Log.d(TAG, "RUN");
}
}
和 AndoridMainfest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.cameraexample"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="17" />
<uses-permission android:name="android.permission.CHANGE_CONFIGURATION"></uses-permission>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.CAMERA" />
<uses-feature android:name="android.hardware.camera" />
<uses-feature android:name="android.hardware.camera.autofocus" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.cameraexample.MainActivity"
android:label="@string/app_name"
android:configChanges="orientation|keyboard|keyboardHidden|screenSize">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
布局
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<FrameLayout
android:id="@+id/camera_preview"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_weight="1"
/>
<Button
android:id="@+id/button_capture"
android:text="Capture"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
/>
</RelativeLayout>