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flutterdartlaunch

Getting blank screen when launching to a physical device

My application was running perfectly fine on my emulator (Google Pixel 2), but when I tried launching the app to a physical device (Galaxy Note 20) I just get white screen, there is probably something going wrong with physical device being much newer than the emulator. I tried :

flutter upgrade 
flutter clean

and changed minSDK to 23 instead of 16. I also tried upgrading the dependences to newer versions, but do to incompatibility issues I had to reset them back to older versions.

When launching to the emulator I get this:

Launching lib\main.dart on Android SDK built for x86 in debug mode...
Running Gradle task 'assembleDebug'...
√ Built build\app\outputs\flutter-apk\app-debug.apk.
Installing build\app\outputs\flutter-apk\app.apk...
Debug service listening on ws://127.0.0.1:54695/lfhRZFuIGMw=/ws
Syncing files to device Android SDK built for x86...
D/EGL_emulation(21851): eglMakeCurrent: 0xebea1000: ver 3 0 (tinfo 0xcc025380)
D/eglCodecCommon(21851): setVertexArrayObject: set vao to 0 (0) 1 0

and when launching to the physical device, this is what I get:

Launching lib\main.dart on SM N985F in debug mode...
Running Gradle task 'assembleDebug'...
√ Built build\app\outputs\flutter-apk\app-debug.apk.
Installing build\app\outputs\flutter-apk\app.apk...
Debug service listening on ws://127.0.0.1:54580/fefT1rs2LOk=/ws
Syncing files to device SM N985F...
E/flutter (22977): [ERROR:flutter/lib/ui/ui_dart_state.cc(186)] Unhandled Exception: NoSuchMethodError: The getter 'length' was called on null.
E/flutter (22977): Receiver: null
E/flutter (22977): Tried calling: length
E/flutter (22977): #0      Object.noSuchMethod (dart:core-patch/object_patch.dart:54:5)
E/flutter (22977): #1      _parseJson (dart:convert-patch/convert_patch.dart:39:28)
E/flutter (22977): #2      JsonDecoder.convert (dart:convert/json.dart:506:36)
E/flutter (22977): #3      JsonCodec.decode (dart:convert/json.dart:157:41)
E/flutter (22977): #4      jsonDecode (dart:convert/json.dart:96:10)
E/flutter (22977): #5      getList (package:realtime_test/main.dart:27:30)
E/flutter (22977): <asynchronous suspension>
E/flutter (22977): #6      main (package:realtime_test/main.dart:16:3)
E/flutter (22977): <asynchronous suspension>
E/flutter (22977): 
I/ViewRootImpl@46a8966[MainActivity](22977): ViewPostIme pointer 0
I/ViewRootImpl@46a8966[MainActivity](22977): MSG_WINDOW_FOCUS_CHANGED 0 1
I/SurfaceControl(22977): release : mNativeObject = 476773762736 - Surface(name=Surface(name=a38c4 InputMethod)/@0x7a23a73 - animation-leash)/@0xa41f0a1 / android.view.-$$Lambda$Rl1VZmNJ0VZDLK0BAbaVGis0rrA.accept:2 android.view.InsetsSourceControl.release:170 android.view.InsetsSourceConsumer.setControl:202 android.view.ImeInsetsSourceConsumer.setControl:154 
I/SurfaceControl(22977): nativeRelease nativeObject s[476773762736]
I/SurfaceControl(22977): nativeRelease nativeObject e[476773762736]
I/SurfaceControl(22977): release : mNativeObject = 476773765760 - Surface(name=Surface(name=2a9e95b NavigationBar0)/@0x87e7f82 - animation-leash)/@0x2190368 / android.view.-$$Lambda$Rl1VZmNJ0VZDLK0BAbaVGis0rrA.accept:2 android.view.InsetsSourceControl.release:170 android.view.InsetsSourceConsumer.setControl:202 android.view.InsetsController.onControlsChanged:833 
I/SurfaceControl(22977): nativeRelease nativeObject s[476773765760]
I/SurfaceControl(22977): nativeRelease nativeObject e[476773765760]
I/SurfaceControl(22977): release : mNativeObject = 476773740672 - Surface(name=Surface(name=6106940 StatusBar)/@0xd1b68b8 - animation-leash)/@0xe205381 / android.view.-$$Lambda$Rl1VZmNJ0VZDLK0BAbaVGis0rrA.accept:2 android.view.InsetsSourceControl.release:170 android.view.InsetsSourceConsumer.setControl:202 android.view.InsetsController.onControlsChanged:833 
I/SurfaceControl(22977): nativeRelease nativeObject s[476773740672]
I/SurfaceControl(22977): nativeRelease nativeObject e[476773740672]
D/InputTransport(22977): Input channel destroyed: 'ClientS', fd=122
I/SurfaceControl(22977): release : mNativeObject = 476773811120 - Surface(name=Surface(name=a38c4 InputMethod)/@0x7a23a73 - animation-leash)/@0x2fda6bd / android.view.-$$Lambda$Rl1VZmNJ0VZDLK0BAbaVGis0rrA.accept:2 android.view.InsetsSourceControl.release:170 android.view.InsetsSourceConsumer.setControl:202 android.view.ImeInsetsSourceConsumer.setControl:154 
I/SurfaceControl(22977): nativeRelease nativeObject s[476773811120]
I/SurfaceControl(22977): nativeRelease nativeObject e[476773811120]
I/SurfaceView(22977): onWindowVisibilityChanged(8) false io.flutter.embedding.android.FlutterSurfaceView{a0c34fd V.E...... ........ 0,0-1440,3035} of ViewRootImpl@46a8966[MainActivity]
I/SurfaceView(22977): surfaceDestroyed callback.size 1 #2 io.flutter.embedding.android.FlutterSurfaceView{a0c34fd V.E...... ........ 0,0-1440,3035}
I/mali_egl(22977): eglDestroySurface() in
I/mali_winsys(22977): delete_surface() [1440x3035] return
I/mali_egl(22977): eglDestroySurface() out
W/libEGL  (22977): EGLNativeWindowType 0x7021f7c4a0 disconnect failed
D/SurfaceControl(22977): hide : mNativeObject = 477310781072 - sc.mNativeObject = 476773737760 - Surface(name=SurfaceView - com.example.realtime_test/com.example.realtime_test.MainActivity@a0c34fd@0)/@0x4db9fa2
D/SurfaceControl(22977): nativeSetFlags Done : Surface(name=SurfaceView - com.example.realtime_test/com.example.realtime_test.MainActivity@a0c34fd@0)/@0x4db9fa2
I/SurfaceView(22977): remove() from RT android.view.SurfaceView$2@1fbc4b2 Surface(name=SurfaceView - com.example.realtime_test/com.example.realtime_test.MainActivity@a0c34fd@0)/@0x4db9fa2
I/SurfaceControl(22977): release : mNativeObject = 476773737760 - Surface(name=SurfaceView - com.example.realtime_test/com.example.realtime_test.MainActivity@a0c34fd@0)/@0x4db9fa2 / android.view.SurfaceControl$Transaction.remove:3449 android.view.SurfaceView$2.positionLost:1561 android.graphics.RenderNode$CompositePositionUpdateListener.positionLost:313 <bottom of call stack> 
I/SurfaceControl(22977): nativeRelease nativeObject s[476773737760]
I/SurfaceControl(22977): nativeRelease nativeObject e[476773737760]
I/SurfaceControl(22977): release : mNativeObject = 476773742576 - Surface(name=Background for -SurfaceView - com.example.realtime_test/com.example.realtime_test.MainActivity@a0c34fd@0)/@0x1cd2c03 / android.view.SurfaceControl$Transaction.remove:3449 android.view.SurfaceView$2.positionLost:1562 android.graphics.RenderNode$CompositePositionUpdateListener.positionLost:313 <bottom of call stack> 
I/SurfaceControl(22977): nativeRelease nativeObject s[476773742576]
I/SurfaceControl(22977): nativeRelease nativeObject e[476773742576]
I/mali_egl(22977): eglDestroySurface() in
I/mali_winsys(22977): delete_surface() [1440x3088] return
I/mali_egl(22977): eglDestroySurface() out
W/libEGL  (22977): EGLNativeWindowType 0x7021f7a290 disconnect failed
I/SurfaceControl(22977): release : mNativeObject = 476773781888 - Surface(name=null)/@0x516d780 / android.view.SurfaceControl.assignNativeObject:567 android.view.SurfaceControl.readFromParcel:1115 android.view.IWindowSession$Stub$Proxy.relayout:1777 android.view.ViewRootImpl.relayoutWindow:8953 
I/SurfaceControl(22977): nativeRelease nativeObject s[476773781888]
I/SurfaceControl(22977): nativeRelease nativeObject e[476773781888]
I/SurfaceControl(22977): assignNativeObject: nativeObject = 0 Surface(name=null)/@0x516d780 / android.view.SurfaceControl.readFromParcel:1115 android.view.IWindowSession$Stub$Proxy.relayout:1777 android.view.ViewRootImpl.relayoutWindow:8953 android.view.ViewRootImpl.performTraversals:3312 android.view.ViewRootImpl.doTraversal:2575 android.view.ViewRootImpl$TraversalRunnable.run:9910 android.view.Choreographer$CallbackRecord.run:1010 android.view.Choreographer.doCallbacks:809 android.view.Choreographer.doFrame:744 android.view.Choreographer$FrameDisplayEventReceiver.run:995 
I/SurfaceControl(22977): assignNativeObject: nativeObject = 0 Surface(name=null)/@0x8186ac0 / android.view.SurfaceControl.readFromParcel:1115 android.view.IWindowSession$Stub$Proxy.relayout:1787 android.view.ViewRootImpl.relayoutWindow:8953 android.view.ViewRootImpl.performTraversals:3312 android.view.ViewRootImpl.doTraversal:2575 android.view.ViewRootImpl$TraversalRunnable.run:9910 android.view.Choreographer$CallbackRecord.run:1010 android.view.Choreographer.doCallbacks:809 android.view.Choreographer.doFrame:744 android.view.Choreographer$FrameDisplayEventReceiver.run:995 
I/SurfaceControl(22977): release : mNativeObject = 476773737200 - Surface(name=Bounds for - com.example.realtime_test/com.example.realtime_test.MainActivity@0)/@0xd62f1b9 / android.view.ViewRootImpl.destroySurface:2437 android.view.ViewRootImpl.relayoutWindow:8990 android.view.ViewRootImpl.performTraversals:3312 android.view.ViewRootImpl.doTraversal:2575 
I/SurfaceControl(22977): nativeRelease nativeObject s[476773737200]
I/SurfaceControl(22977): nativeRelease nativeObject e[476773737200]
I/ViewRootImpl@46a8966[MainActivity](22977): Relayout returned: old=(0,0,1440,3088) new=(0,0,1440,3088) req=(1440,3088)8 dur=6 res=0x5 s={false 0} ch=true fn=2
I/SurfaceView(22977): windowStopped(true) false io.flutter.embedding.android.FlutterSurfaceView{a0c34fd V.E...... ........ 0,0-1440,3035} of ViewRootImpl@46a8966[MainActivity]
I/ViewRootImpl@46a8966[MainActivity](22977): stopped(true) old=false

So there is clearly something going wrong but I don't know what's the issue.

Solution

    • You're white screen is showing up because your app can't get past the initial functions you are performing on launch.

    • The error message says getter length called on null, and then it breaks in your main.dart at line #27. Reading further into the error, you are calling a jsonDecode, but it's not receiving anything, causing your app to crash and not load the home page.

    • It's not technically crashing, but it's waiting for the logic on line #27 to finish, but it's not finishing. Since it's saying getter length was called on null most likely also means that you are performing logic on in a for loop, or checking if something isEmpty or isNotEmpty, when it comes to check these properties, the iterable it's trying to check is null at the time of calling this function.

    • Double check there first, this is most likely due to a bug you encountered while working on the emulator, fixed it then and got the emulator to work, but didn't solve the problem for your new users, who are using a fresh install, such as your physical device.

    • If you are fetching data from a database, and used initial dummy data while developing on the emulator, and forgot to add that for new devices, this should solve your problem, and I would start looking there.

    • Another thing to keep in mind, when your app compiles and builds successfully, your problem is not in dependencies or SDK versions or other things related to your build gradle. And your error said this √ Built build\app.... , so the problem is not being caused build time malfunctioning, but runtime errors.