我们刚刚在工作中运行了一些运行4.3的三星Galaxy S4，我们正在使用移动管理系统，出于安全原因禁用摄像头。我已经创建了一个FlashLight应用程序（在我的HTC和Nexus 10上运行正常）我想使用，但是我收到了一个错误。
有趣的是，如果我使用三星内置的“辅助光”小部件，它可以正常工作。因此，即使禁用相机，LED仍然可以工作，所以它可能，我只是不知道如何。我知道有些人可能会说，为什么不只是使用小部件...我只是不喜欢那个庞大的小部件，并希望拥有自己的应用程序。
以下是我在清单中的权限
<uses-feature android:name="android.hardware.camera" android:required="false"/>
<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.permission.FLASHLIGHT"/>
<uses-permission android:name="android.permission.VIBRATE"/>
<uses-permission android:name="android.permission.WAKE_LOCK" />
这是我的MainActivity.java
package com.company.flashlight;
import java.io.IOException;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.graphics.Color;
import android.hardware.Camera;
import android.hardware.Camera.Parameters;
import android.media.MediaPlayer;
import android.media.MediaPlayer.OnCompletionListener;
import android.os.Build;
import android.os.Bundle;
import android.os.PowerManager;
import android.os.Vibrator;
import android.util.Log;
import android.view.Gravity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.SurfaceHolder;
import android.view.SurfaceHolder.Callback;
import android.view.SurfaceView;
import android.view.View;
import android.widget.ImageButton;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends Activity implements Callback {
public static Camera camera;
private boolean isFlashOn;
private boolean hasFlash;
private SurfaceView sView;
private SurfaceHolder sHolder;
private PowerManager.WakeLock wl;
Parameters params;
MediaPlayer mp;
ImageButton btnSwitch;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
wl = pm.newWakeLock(PowerManager.FULL_WAKE_LOCK, "DoNjfdhotDimScreen");
// flash switch button
btnSwitch = (ImageButton) findViewById(R.id.btnSwitch);
sView = (SurfaceView) findViewById(R.id.PREVIEW);
sHolder = sView.getHolder();
// First check if device is supporting flashlight or not
hasFlash = getApplicationContext().getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA_FLASH);
if (!hasFlash) {
// device doesn't have or support a LED flash
Toast toast = Toast.makeText(this, (R.string.no_flash_message), Toast.LENGTH_LONG);
toast.setGravity(Gravity.CENTER, 0, 0);
toast.show();
// Show message and sho2w a white screen
TextView txtBkupLight=(TextView)findViewById(R.id.tvBkupLightSrc);
txtBkupLight.setVisibility(View.VISIBLE);
txtBkupLight.setHeight(1920);
txtBkupLight.setBackgroundColor(Color.WHITE);
} else {
// get the camera
getCamera();
// displaying power button image
togglePowerButtonImage();
// Switch button click event to toggle flash on/off
btnSwitch.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (isFlashOn) {
// turn off flash
turnOffFlash();
} else {
// turn on flash
turnOnFlash();
}
}
});
}
}
// Get the camera
private void getCamera() {
if (camera == null) {
try {
sHolder.addCallback(this);
if(Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB)
sHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
params.setFocusMode(Camera.Parameters.FOCUS_MODE_INFINITY);
camera = Camera.open();
try {
camera.setPreviewDisplay(sHolder);
} catch (IOException e) {
e.printStackTrace();
}
params = camera.getParameters();
} catch (RuntimeException e) {
String err = (e.getMessage()==null)?"Camera failed":e.getMessage();
Log.e("Camera Error. Failed to Open. Error: ", err);
}
}
}
// Turning On flash
private void turnOnFlash() {
if (!isFlashOn) {
if (camera == null || params == null) {
return;
}
// check to see if the device can vibrate
if ( getSystemService(VIBRATOR_SERVICE) != null ) {
// vibrate device
powerVibrate();
}else{
// play sound
playSound();
}
params = camera.getParameters();
params.setFlashMode(Parameters.FLASH_MODE_TORCH);
camera.setParameters(params);
camera.startPreview();
isFlashOn = true;
// changing button/switch image
togglePowerButtonImage();
}
}
// Turning Off flash
private void turnOffFlash() {
if (isFlashOn) {
if (camera == null || params == null) {
return;
}
// check to see if the device can vibrate
if ( getSystemService(VIBRATOR_SERVICE) != null ) {
// vibrate device
powerVibrate();
}else{
// play sound
playSound();
}
params = camera.getParameters();
params.setFlashMode(Parameters.FLASH_MODE_OFF);
camera.setParameters(params);
camera.stopPreview();
isFlashOn = false;
// changing button/switch image
togglePowerButtonImage();
}
}
// Vibrate Phone
public void powerVibrate() {
if(isFlashOn){
Vibrator vib = (Vibrator) this.getSystemService(VIBRATOR_SERVICE);
vib.vibrate(50);
}else{
Vibrator vib = (Vibrator) this.getSystemService(VIBRATOR_SERVICE);
vib.vibrate(50);
}
}
// Playing sound
// will play button toggle sound on flash on / off
private void playSound(){
if(isFlashOn){
mp = MediaPlayer.create(MainActivity.this, R.raw.light_switch_off);
}else{
mp = MediaPlayer.create(MainActivity.this, R.raw.light_switch_on);
}
mp.setOnCompletionListener(new OnCompletionListener() {
@Override
public void onCompletion(MediaPlayer mp) {
mp.release();
}
});
mp.start();
}
/*
* Toggle switch power button images
* changing image states to on / off
* */
private void togglePowerButtonImage(){
if(isFlashOn){
btnSwitch.setImageResource(R.drawable.flashlight_on);
}else{
btnSwitch.setImageResource(R.drawable.flashlight_off);
}
}
@Override
protected void onDestroy() {
super.onDestroy();
}
@Override
protected void onPause() {
super.onPause();
wl.release();
// on pause turn off the flash
turnOffFlash();
}
@Override
protected void onRestart() {
super.onRestart();
}
@Override
protected void onResume() {
super.onResume();
wl.acquire();
// on resume turn on the flash
if(hasFlash)
turnOnFlash();
}
@Override
protected void onStart() {
super.onStart();
// on starting the app get the camera params
getCamera();
}
@Override
protected void onStop() {
super.onStop();
// on stop release the camera
if (camera != null) {
camera.release();
camera = null;
}
}
@Override
public void surfaceChanged(SurfaceHolder arg0, int arg1, int arg2, int arg3) {
}
@Override
public void surfaceCreated(SurfaceHolder arg0) {
try {
camera.setPreviewDisplay(sHolder);
} catch (IOException e) {
e.printStackTrace();
}
}
@Override
public void surfaceDestroyed(SurfaceHolder arg0) {
if (camera != null) {
camera.release();
camera = null;
}
}
public boolean onOptionsItemSelected(MenuItem item){
switch(item.getItemId()){
case R.id.menuAbout:
startActivity(new Intent(MainActivity.this, About.class));
return true;
case R.id.menuExit:
finish();
}
return false;
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
这是我的布局文件activity_main.xml
<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:background="@drawable/radial_background"
tools:context=".MainActivity" >
<SurfaceView
android:id="@+id/PREVIEW"
android:layout_width="1dip"
android:layout_height="1dip"/>
<ImageButton
android:id="@+id/btnSwitch"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:background="@null"
android:contentDescription="@null"
android:src="@drawable/flashlight_on" />
<TextView
android:id="@+id/tvBkupLightSrc"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:background="@android:color/background_dark"
android:textColor="@android:color/primary_text_dark"
android:visibility="invisible" />
</RelativeLayout>
这是我的错误.........
01-18 11:19:26.750: E/Camera Error. Failed to Open. Error:(28886): Camera failed
01-18 11:19:26.780: D/dalvikvm(28886): GC_FOR_ALLOC freed 996K, 27% free 19145K/25948K, paused 16ms, total 16ms
01-18 11:19:26.790: I/dalvikvm-heap(28886): Grow heap (frag case) to 27.489MB for 3686416-byte allocation
01-18 11:19:26.800: E/Camera Error. Failed to Open. Error:(28886): Camera failed
01-18 11:19:27.201: D/libEGL(28886): loaded /vendor/lib/egl/libEGL_adreno.so
01-18 11:19:27.201: D/libEGL(28886): loaded /vendor/lib/egl/libGLESv1_CM_adreno.so
01-18 11:19:27.201: D/libEGL(28886): loaded /vendor/lib/egl/libGLESv2_adreno.so
01-18 11:19:27.201: I/Adreno-EGL(28886): <qeglDrvAPI_eglInitialize:316>: EGL 1.4 QUALCOMM build: (CL4169980)
01-18 11:19:27.201: I/Adreno-EGL(28886): OpenGL ES Shader Compiler Version: 17.01.10.SPL
01-18 11:19:27.201: I/Adreno-EGL(28886): Build Date: 09/26/13 Thu
01-18 11:19:27.201: I/Adreno-EGL(28886): Local Branch:
01-18 11:19:27.201: I/Adreno-EGL(28886): Remote Branch:
01-18 11:19:27.201: I/Adreno-EGL(28886): Local Patches:
01-18 11:19:27.201: I/Adreno-EGL(28886): Reconstruct Branch:
01-18 11:19:27.251: D/OpenGLRenderer(28886): Enabling debug mode 0
01-18 11:19:27.261: D/AndroidRuntime(28886): Shutting down VM
01-18 11:19:27.261: W/dalvikvm(28886): threadid=1: thread exiting with uncaught exception (group=0x4179f898)
01-18 11:19:27.261: E/AndroidRuntime(28886): FATAL EXCEPTION: main
01-18 11:19:27.261: E/AndroidRuntime(28886): java.lang.NullPointerException
01-18 11:19:27.261: E/AndroidRuntime(28886): at com.company.flashlight.MainActivity.surfaceCreated(MainActivity.java:272)
01-18 11:19:27.261: E/AndroidRuntime(28886): at android.view.SurfaceView.updateWindow(SurfaceView.java:610)
01-18 11:19:27.261: E/AndroidRuntime(28886): at android.view.SurfaceView.access$000(SurfaceView.java:93)
01-18 11:19:27.261: E/AndroidRuntime(28886): at android.view.SurfaceView$3.onPreDraw(SurfaceView.java:182)
01-18 11:19:27.261: E/AndroidRuntime(28886): at android.view.ViewTreeObserver.dispatchOnPreDraw(ViewTreeObserver.java:864)
01-18 11:19:27.261: E/AndroidRuntime(28886): at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2140)
01-18 11:19:27.261: E/AndroidRuntime(28886): at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1247)
01-18 11:19:27.261: E/AndroidRuntime(28886): at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6355)
01-18 11:19:27.261: E/AndroidRuntime(28886): at android.view.Choreographer$CallbackRecord.run(Choreographer.java:791)
01-18 11:19:27.261: E/AndroidRuntime(28886): at android.view.Choreographer.doCallbacks(Choreographer.java:591)
01-18 11:19:27.261: E/AndroidRuntime(28886): at android.view.Choreographer.doFrame(Choreographer.java:561)
01-18 11:19:27.261: E/AndroidRuntime(28886): at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:777)
01-18 11:19:27.261: E/AndroidRuntime(28886): at android.os.Handler.handleCallback(Handler.java:730)
01-18 11:19:27.261: E/AndroidRuntime(28886): at android.os.Handler.dispatchMessage(Handler.java:92)
01-18 11:19:27.261: E/AndroidRuntime(28886): at android.os.Looper.loop(Looper.java:137)
01-18 11:19:27.261: E/AndroidRuntime(28886): at android.app.ActivityThread.main(ActivityThread.java:5419)
01-18 11:19:27.261: E/AndroidRuntime(28886): at java.lang.reflect.Method.invokeNative(Native Method)
01-18 11:19:27.261: E/AndroidRuntime(28886): at java.lang.reflect.Method.invoke(Method.java:525)
01-18 11:19:27.261: E/AndroidRuntime(28886): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1187)
01-18 11:19:27.261: E/AndroidRuntime(28886): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
01-18 11:19:27.261: E/AndroidRuntime(28886): at dalvik.system.NativeStart.main(Native Method)
答案 0 :(得分：0)
NullPointerException中的第272行有一个MainActivity.java。发生这种情况是因为调用camera时null为surfaceCreated。