質問
I'm having an error while trying to get an intent from another application. At start, I had the intent to run the IP camera stream, and it worked like a charm. But later when I click on the screen to get a snapshot, click yes to share and then cancel the sharing intent to go back to the IP camera stream, I get an error there NullPointerException.
Here is my code:
https://stackoverflow.com/questions/23632615
italiano
english
français
española
中国
日本の
العربية
Deutsch
한국어
Português
Russianpublic class Activity_streamCam extends Activity {
private static final boolean DEBUG = false;
Activity activity;
final Context context = this;
URL url_snap;
private static final String TAG = "MJPEG";
PowerManager powerManager = null;
WakeLock wakeLock = null;
String URL1, test, URL2;
private boolean suspending = false;
private MjpegView mv;
@SuppressWarnings("deprecation")
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(R.layout.stream_camera);
this.powerManager = (PowerManager) this
.getSystemService(Context.POWER_SERVICE);
this.wakeLock = this.powerManager.newWakeLock(
PowerManager.FULL_WAKE_LOCK, "My Lock");
Intent intent = getIntent();
// URL1 = intent.getExtras().getString("key");
Bundle extras = intent.getExtras();
if (extras != null) {
URL1 = extras.getString("key");
// Check for presence of URL1
if (URL1 != null) {
test = URL1 + "axis-cgi/mjpg/video.cgi?resolution=320x240";
}
}
mv = (MjpegView) findViewById(R.id.mv);
new DoRead().execute(test);
mv.setOnTouchListener(new View.OnTouchListener() {
@SuppressLint("Wakelock")
@Override
public boolean onTouch(View v, MotionEvent event) {
try {
url_snap = new URL(
"http://plazacam.studentaffairs.duke.edu/axis-cgi/jpg/image.cgi?resolution=320x240");
Bitmap bmp = snapShotManager.takeSnapshot(url_snap);
final File share = snapShotManager.saveSnap(bmp);
AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(
context);
// set title
alertDialogBuilder.setTitle("Success snapshot");
// set dialog message
alertDialogBuilder
.setMessage("Would you like to share it ?")
.setCancelable(true)
.setPositiveButton("Yes",
new DialogInterface.OnClickListener() {
public void onClick(
DialogInterface dialog, int id) {
mv.stopPlayback();
mv.destroyDrawingCache();
Intent sendIntent = new Intent(
Intent.ACTION_SEND);
sendIntent.setType("image/jpeg");
sendIntent.putExtra(
Intent.EXTRA_STREAM, Uri
.parse("file://"
+ share));
sendIntent
.putExtra(
Intent.EXTRA_TEXT,
"This snapshot was taken by DroidCamViewer app, check it out ! :)");
try {
startActivity(Intent
.createChooser(
sendIntent,
"share"));
} catch (Exception e) {
}
}
})
.setNegativeButton("No",
new DialogInterface.OnClickListener() {
public void onClick(
DialogInterface dialog, int id) {
dialog.cancel();
}
});
AlertDialog alertDialog = alertDialogBuilder.create();
alertDialog.show();
} catch (IOException e) {
Log.i(getString(R.string.logTag), "Snap I/O exception !!");
e.printStackTrace();
}
return false;
}
});
}
public void onResume() {
if (DEBUG)
Log.d(TAG, "onResume()");
super.onResume();
if (mv != null) {
if (suspending) {
suspending = false;
new RestartApp().execute();
this.wakeLock.acquire();
}
}
}
public void onStart() {
if (DEBUG)
Log.d(TAG, "onStart()");
super.onStart();
}
public void onPause() {
if (DEBUG)
Log.d(TAG, "onPause()");
super.onPause();
}
public void onStop() {
if (DEBUG)
Log.d(TAG, "onStop()");
super.onStop();
}
public void onRestart() {
if (DEBUG)
Log.d(TAG, "onRestart()");
super.onRestart();
if (mv != null) {
if (suspending) {
suspending = false;
new RestartApp().execute();
this.wakeLock.acquire();
}
}
}
public void onDestroy() {
if (DEBUG)
Log.d(TAG, "onDestroy()");
super.onDestroy();
mv.stopPlayback();
mv.destroyDrawingCache();
}
public class DoRead extends AsyncTask<String, Void, MjpegInputStream> {
protected MjpegInputStream doInBackground(String... url) {
HttpResponse res = null;
DefaultHttpClient httpclient = new DefaultHttpClient();
HttpParams httpParams = httpclient.getParams();
HttpConnectionParams.setConnectionTimeout(httpParams, 5 * 1000);
Log.d(TAG, "1. Sending http request");
try {
res = httpclient.execute(new HttpGet(URI.create(url[0])));
Log.d(TAG, "2. Request finished, status = "
+ res.getStatusLine().getStatusCode());
if (res.getStatusLine().getStatusCode() == 401) {
return null;
}
return new MjpegInputStream(res.getEntity().getContent());
} catch (ClientProtocolException e) {
e.printStackTrace();
Log.d(TAG, "Request failed-ClientProtocolException", e);
// Error connecting to camera
} catch (IOException e) {
e.printStackTrace();
Log.d(TAG, "Request failed-IOException", e);
// Error connecting to camera
}
return null;
}
protected void onPostExecute(MjpegInputStream result) {
mv.setSource(result);
if (result != null)
result.setSkip(1);
mv.setDisplayMode(MjpegView.SIZE_BEST_FIT);
mv.showFps(true);
}
}
public class RestartApp extends AsyncTask<Void, Void, Void> {
protected Void doInBackground(Void... v) {
Activity_streamCam.this.finish();
return null;
}
protected void onPostExecute(Void v) {
startActivity((new Intent(Activity_streamCam.this,
Activity_streamCam.class)));
}
}
}
The NullPointerException results when I click yes on the alert box and then cancel the intent or share the bitmap to go back to the stream.
Here is my logcat
05-13 13:23:13.831: E/AndroidRuntime(276): FATAL EXCEPTION: main
05-13 13:23:13.831: E/AndroidRuntime(276): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.marwen.droidcamviewer/com.marwen.droidcamviewer.Activity_streamCam}: java.lang.NullPointerException
05-13 13:23:13.831: E/AndroidRuntime(276): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
05-13 13:23:13.831: E/AndroidRuntime(276): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
05-13 13:23:13.831: E/AndroidRuntime(276): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
05-13 13:23:13.831: E/AndroidRuntime(276): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
05-13 13:23:13.831: E/AndroidRuntime(276): at android.os.Handler.dispatchMessage(Handler.java:99)
05-13 13:23:13.831: E/AndroidRuntime(276): at android.os.Looper.loop(Looper.java:123)
05-13 13:23:13.831: E/AndroidRuntime(276): at android.app.ActivityThread.main(ActivityThread.java:4627)
05-13 13:23:13.831: E/AndroidRuntime(276): at java.lang.reflect.Method.invokeNative(Native Method)
05-13 13:23:13.831: E/AndroidRuntime(276): at java.lang.reflect.Method.invoke(Method.java:521)
05-13 13:23:13.831: E/AndroidRuntime(276): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
05-13 13:23:13.831: E/AndroidRuntime(276): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
05-13 13:23:13.831: E/AndroidRuntime(276): at dalvik.system.NativeStart.main(Native Method)
05-13 13:23:13.831: E/AndroidRuntime(276): Caused by: java.lang.NullPointerException
05-13 13:23:13.831: E/AndroidRuntime(276): at com.marwen.droidcamviewer.Activity_streamCam.onCreate(Activity_streamCam.java:66)
05-13 13:23:13.831: E/AndroidRuntime(276): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
05-13 13:23:13.831: E/AndroidRuntime(276): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
05-13 13:23:13.831: E/AndroidRuntime(276): ... 11 more
Android Manifest:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.marwen.droidcamviewer"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="19" />
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.marwen.droidcamviewer.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".Activity_setPreference"
android:label="@string/title_activity_main" >
</activity>
<activity
android:name="Activity_streamCam"
android:label="@string/title_activity_streamCam"
android:screenOrientation="landscape" >
</activity>
<activity
android:name="Activity_addCam"
android:label="@string/title_activity_addCam" >
</activity>
<activity
android:name="Activity_about"
android:label="@string/title_activity_about" >
</activity>
<activity
android:name="Activity_Camera_list"
android:label="@string/title_activity_about" >
</activity>
<activity
android:name="EditCam"
android:label="@string/title_activity_EditCam" >
</activity>
<activity
android:name="Activity_manageCam"
android:label="@string/title_activity_manageCam" >
</activity>
</application>
</manifest>
解決
It is possible that you've got an Intent without extras. When you do this:
URL1 = intent.getExtras().getString("key");
You will get a NullPointerException if the Intent has no extras.
To prevent this, do:
Bundle extras = intent.getExtras();
if (extras != null) {
URL1 = extras.getString("key");
// Check for presence of URL1
if (URL1 != null) {
// Here you can be sure not to get NullPointerException
}
}
This is just good defensive programming.
