我有一个应用程序，它是一个火炬。我添加了一项功能，如果用户没有设备中的闪光灯，那么它应该启动前屏幕手电筒。这是我的代码..
LightsOn.java
public class LightsOn extends Activity implements OnKeyListener
{
ImageView button;
Boolean flashon=true;
private boolean hasFlash;
Parameters myparas;
private Camera mycamera;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_light);
hasFlash = getApplicationContext().getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA_FLASH);
button=(ImageView)findViewById(R.id.power);
button.setBackgroundResource(R.drawable.offswitch);
button.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v)
{
// TODO Auto-generated method stub
if(flashon)
{
button.setBackgroundResource(R.drawable.onswitch);
if (mycamera == null || myparas == null)
{
return;
}
else
{
myparas = mycamera.getParameters();
myparas.setFlashMode(Parameters.FLASH_MODE_OFF);
mycamera.setParameters(myparas);
mycamera.stopPreview();
flashon=false;
}
}
else
{
button.setBackgroundResource(R.drawable.offswitch);
if (mycamera == null || myparas == null)
{
return;
}
else
{
myparas = mycamera.getParameters();
myparas.setFlashMode(Parameters.FLASH_MODE_TORCH);
mycamera.setParameters(myparas);
mycamera.startPreview();
flashon=true;
}
}
}
});
}
private void getCamera()
{
if (mycamera == null)
{
try
{
mycamera = Camera.open();
myparas = mycamera.getParameters();
}
catch (RuntimeException e)
{
Log.e("Camera Error. Failed to Open. Error: ", e.getMessage());
}
}
if (!hasFlash)
{
AlertDialog.Builder dialog = new AlertDialog.Builder(this);
dialog.setTitle("Sorry your device doesnt support flash. Do you want to use your front screen as torch.?");
dialog.setMessage("Press 'OKAY' to exit..");
dialog.setPositiveButton("Use screen", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id)
{
Intent intent = new Intent(LightsOn.this,FrontScreen.class);
startActivity(intent);
}
});
dialog.setNegativeButton("More Apps by AKSHAT JAISWAL", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id)
{
String page="https://play.google.com/store/apps/developer?id=Akshat+Jaiswal#?t=W251bGwsbnVsbCxudWxsLDEsImFrc2hhdC5qYWlzd2FsLnNob3dtZXRoYXRhcHAiXQ..";
Intent newIntent= new Intent();
newIntent.setAction(Intent.ACTION_VIEW);
newIntent.setData(android.net.Uri.parse(page));
Uri.parse(page);
startActivity(newIntent);
finish();
moveTaskToBack(true);
}
});
dialog.setNeutralButton("Exit", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int id)
{
finish();
moveTaskToBack(true);
}
});
dialog.show();
}
}
@Override
protected void onDestroy() {
super.onDestroy();
}
@Override
protected void onPause()
{
super.onPause();
}
@Override
protected void onRestart() {
super.onRestart();
}
@Override
protected void onResume() {
super.onResume();
if(hasFlash)
myparas = mycamera.getParameters();
myparas.setFlashMode(Parameters.FLASH_MODE_TORCH);
mycamera.setParameters(myparas);
mycamera.startPreview();
flashon=true;
}
@Override
protected void onStop()
{
super.onStop();
}
@Override
protected void onStart() {
super.onStart();
// on starting the app get the camera params
getCamera();
}
@Override
public boolean onCreateOptionsMenu(Menu m)
{
MenuInflater inf=getMenuInflater();
inf.inflate(R.menu.menu,m);
return true;
}
public boolean onOptionsItemSelected(MenuItem itm)
{
if(itm.getItemId()==R.id.it1)
{
if(flashon)
{
button.setBackgroundResource(R.drawable.onswitch);
if (mycamera == null || myparas == null)
{
return false;
}
else
{
myparas = mycamera.getParameters();
myparas.setFlashMode(Parameters.FLASH_MODE_OFF);
mycamera.setParameters(myparas);
mycamera.stopPreview();
flashon=false;
}
}
else
{
button.setBackgroundResource(R.drawable.offswitch);
if (mycamera == null || myparas == null)
{
return false;
}
else
{
myparas = mycamera.getParameters();
myparas.setFlashMode(Parameters.FLASH_MODE_TORCH);
mycamera.setParameters(myparas);
mycamera.startPreview();
flashon=true;
}
}
}
else if(itm.getItemId()==R.id.it2)
{
Intent intent = new Intent(LightsOn.this,FrontScreen.class);
startActivity(intent);
}
else if(itm.getItemId()==R.id.it3)
{
Toast.makeText(getApplicationContext(), "Website getting launched soon..!!", Toast.LENGTH_SHORT).show();
//String page="http://www.akshatjaiswal.in";
//Intent newIntent= new Intent();
//newIntent.setAction(Intent.ACTION_VIEW);
//newIntent.setData(android.net.Uri.parse(page));
//Uri.parse(page);
//startActivity(newIntent);
}
else if(itm.getItemId()==R.id.it4)
{
String page="https://play.google.com/store/apps/developer?id=Akshat+Jaiswal#?t=W251bGwsbnVsbCxudWxsLDEsImFrc2hhdC5qYWlzd2FsLnNob3dtZXRoYXRhcHAiXQ..";
Intent newIntent= new Intent();
newIntent.setAction(Intent.ACTION_VIEW);
newIntent.setData(android.net.Uri.parse(page));
Uri.parse(page);
startActivity(newIntent);
}
else if(itm.getItemId()==R.id.it5)
{
openDialog();
}
return true;
}
private void openDialog(){
final Dialog dialog = new Dialog(LightsOn.this);
dialog.setTitle("Thank You..");
dialog.setContentView(R.layout.dialoglayout);
dialog.getWindow().getAttributes().windowAnimations = R.style.DialogAnimation;
Button btnDismiss = (Button)dialog.getWindow().findViewById(R.id.exit);
Button btnCancel = (Button)dialog.getWindow().findViewById(R.id.cancel);
btnDismiss.setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View v)
{
if(flashon)
{
button.setBackgroundResource(R.drawable.onswitch);
if (mycamera == null || myparas == null)
{
return;
}
else
{
myparas = mycamera.getParameters();
myparas.setFlashMode(Parameters.FLASH_MODE_OFF);
mycamera.setParameters(myparas);
mycamera.stopPreview();
mycamera.release();
finish();
moveTaskToBack(true);
}
}
else
{
myparas = mycamera.getParameters();
myparas.setFlashMode(Parameters.FLASH_MODE_OFF);
mycamera.setParameters(myparas);
mycamera.stopPreview();
mycamera.release();
finish();
moveTaskToBack(true);
}
}});
btnCancel.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
dialog.dismiss();
}});
dialog.show();
}
@Override
public boolean onKey(DialogInterface dialog, int keyCode, KeyEvent event) {
// TODO Auto-generated method stub
return false;
}
@Override
public void onBackPressed()
{
// TODO Auto-generated method stub
super.onBackPressed();
myparas = mycamera.getParameters();
myparas.setFlashMode(Parameters.FLASH_MODE_OFF);
mycamera.setParameters(myparas);
mycamera.stopPreview();
flashon = false;
if (mycamera != null) {
mycamera.release();
mycamera = null;
}
Log.d("Camera","Back Pressed");
}
}
现在，如果用户没有闪光灯，则会启动此课程。
FrontScreen.java
public class FrontScreen extends Activity
{
Boolean torchon=false;
ImageView button;
RelativeLayout lyt;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.frontscreen);
lyt=(RelativeLayout)findViewById(R.id.layout);
button=(ImageView)findViewById(R.id.power);
button.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
if(torchon)
{
lyt.setBackgroundResource(R.drawable.background);
torchon=false;
}
else
{
lyt.setBackgroundResource(R.drawable.fronttorch);
torchon=true;
}
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu m)
{
MenuInflater inf=getMenuInflater();
inf.inflate(R.menu.frontmenu,m);
return true;
}
public boolean onOptionsItemSelected(MenuItem itm)
{
if(itm.getItemId()==R.id.it1)
{
if(torchon)
{
lyt.setBackgroundResource(R.drawable.background);
torchon=false;
}
else
{
lyt.setBackgroundResource(R.drawable.fronttorch);
torchon=true;
}
}
**else if(itm.getItemId()==R.id.it2)
{
Intent intents = new Intent(FrontScreen.this,LightsOn.class);
startActivity(intents);
}**
else if(itm.getItemId()==R.id.it3)
{
Toast.makeText(getApplicationContext(), "Website getting launched soon..!!", Toast.LENGTH_SHORT).show();
}
else if(itm.getItemId()==R.id.it4)
{
}
else if(itm.getItemId()==R.id.it5)
{
openDialog();
}
return true;
}
private void openDialog(){
final Dialog dialog = new Dialog(FrontScreen.this);
dialog.setTitle("Thank You..");
dialog.setContentView(R.layout.dialoglayout);
dialog.getWindow().getAttributes().windowAnimations = R.style.DialogAnimation;
Button btnDismiss = (Button)dialog.getWindow().findViewById(R.id.exit);
Button btnCancel = (Button)dialog.getWindow().findViewById(R.id.cancel);
btnDismiss.setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View v)
{
if(torchon)
{
lyt.setBackgroundResource(R.drawable.background);
}
else
{
finish();
moveTaskToBack(true);
}
}});
btnCancel.setOnClickListener(new OnClickListener(){
@Override
public void onClick(View v) {
dialog.dismiss();
}});
dialog.show();
}
}
现在当我从这个类中调用第一个类时，它在选项菜单项2中，显示出NullPointerException ..
这是我的logcat消息
07-10 13:27:40.111: W/dalvikvm(17187): threadid=1: thread exiting with uncaught exception (group=0x4104e258)
07-10 13:27:40.115: E/AndroidRuntime(17187): FATAL EXCEPTION: main
07-10 13:27:40.115: E/AndroidRuntime(17187): java.lang.RuntimeException: Unable to resume activity {akshat.jaiswal.showmethatapp/akshat.jaiswal.showmethatapp.LightsOn}: java.lang.NullPointerException
07-10 13:27:40.115: E/AndroidRuntime(17187): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2595)
07-10 13:27:40.115: E/AndroidRuntime(17187): at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2623)
07-10 13:27:40.115: E/AndroidRuntime(17187): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2109)
07-10 13:27:40.115: E/AndroidRuntime(17187): at android.app.ActivityThread.access$600(ActivityThread.java:134)
07-10 13:27:40.115: E/AndroidRuntime(17187): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1247)
07-10 13:27:40.115: E/AndroidRuntime(17187): at android.os.Handler.dispatchMessage(Handler.java:99)
07-10 13:27:40.115: E/AndroidRuntime(17187): at android.os.Looper.loop(Looper.java:154)
07-10 13:27:40.115: E/AndroidRuntime(17187): at android.app.ActivityThread.main(ActivityThread.java:4624)
07-10 13:27:40.115: E/AndroidRuntime(17187): at java.lang.reflect.Method.invokeNative(Native Method)
07-10 13:27:40.115: E/AndroidRuntime(17187): at java.lang.reflect.Method.invoke(Method.java:511)
07-10 13:27:40.115: E/AndroidRuntime(17187): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:809)
07-10 13:27:40.115: E/AndroidRuntime(17187): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:576)
07-10 13:27:40.115: E/AndroidRuntime(17187): at dalvik.system.NativeStart.main(Native Method)
07-10 13:27:40.115: E/AndroidRuntime(17187): Caused by: java.lang.NullPointerException
07-10 13:27:40.115: E/AndroidRuntime(17187): at akshat.jaiswal.showmethatapp.LightsOn.onResume(LightsOn.java:169)
07-10 13:27:40.115: E/AndroidRuntime(17187): at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1159)
07-10 13:27:40.115: E/AndroidRuntime(17187): at android.app.Activity.performResume(Activity.java:4553)
07-10 13:27:40.115: E/AndroidRuntime(17187): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2581)
07-10 13:27:40.115: E/AndroidRuntime(17187): ... 12 more
任何人都可以提前帮助我.. Thanx。
答案 0 :(得分：0)
onResume标志，则hasFlash中的代码似乎已执行。如果是这样，onResume应该是这样的
@Override
protected void onResume() {
super.onResume();
if(hasFlash){
myparas = mycamera.getParameters();
myparas.setFlashMode(Parameters.FLASH_MODE_TORCH);
mycamera.setParameters(myparas);
mycamera.startPreview();
flashon=true;
}
}