Frank Stefan Frank Stefan - 1 month ago 7
Android Question

How create a custom view in an Android application?

I've been trying to create a custom view for 3 days. I've followed every single tutorial but I keep getting the error "ClassNotFoundException". I want to make a joystick, but to simplify this question, I tried to extend a

Button
and use it, at which I couldn't succeed.

MainActivity.java:

package com.stefan.example;

import android.content.Context;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.AttributeSet;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

public class CustomButton extends Button
{
public CustomButton(Context context) {
super(context);
}

public CustomButton(Context context, AttributeSet attrs) {
super(context, attrs);
}

public CustomButton(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
}

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
}


acitivity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<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="com.stefan.example.MainActivity">

<com.stefan.example.MainActivity.CustomButton
android:layout_width="match_parent"
android:layout_height="match_parent" />
</RelativeLayout>


It does not complain at compiling at all, but as soon as I start the app, it crashes with this error:

10-14 17:31:58.476 15869-15869/com.stefan.example E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.stefan.example, PID: 15869
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.stefan.example/com.stefan.example.MainActivity}: android.view.InflateException: Binary XML file line #12: Error inflating class com.stefan.example.MainActivity.CustomButton
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2306)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2366)
at android.app.ActivityThread.access$800(ActivityThread.java:149)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1284)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5297)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:908)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:703)
Caused by: android.view.InflateException: Binary XML file line #12: Error inflating class com.stefan.example.MainActivity.CustomButton
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:757)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:806)
at android.view.LayoutInflater.inflate(LayoutInflater.java:504)
at android.view.LayoutInflater.inflate(LayoutInflater.java:414)
at android.view.LayoutInflater.inflate(LayoutInflater.java:365)
at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:280)
at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140)
at com.stefan.example.MainActivity.onCreate(MainActivity.java:30)
at android.app.Activity.performCreate(Activity.java:6020)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2259)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2366) 
at android.app.ActivityThread.access$800(ActivityThread.java:149) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1284) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:135) 
at android.app.ActivityThread.main(ActivityThread.java:5297) 
at java.lang.reflect.Method.invoke(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:372) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:908) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:703) 
Caused by: java.lang.ClassNotFoundException: Didn't find class "com.stefan.example.MainActivity.CustomButton" on path: DexPathList[[zip file "/data/app/com.stefan.example-1/base.apk"],nativeLibraryDirectories=[/vendor/lib, /system/lib]]
at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
at java.lang.ClassLoader.loadClass(ClassLoader.java:469)
at android.view.LayoutInflater.createView(LayoutInflater.java:571)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:743)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:806) 
at android.view.LayoutInflater.inflate(LayoutInflater.java:504) 
at android.view.LayoutInflater.inflate(LayoutInflater.java:414) 
at android.view.LayoutInflater.inflate(LayoutInflater.java:365) 
at android.support.v7.app.AppCompatDelegateImplV7.setContentView(AppCompatDelegateImplV7.java:280) 
at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140) 
at com.stefan.example.MainActivity.onCreate(MainActivity.java:30) 
at android.app.Activity.performCreate(Activity.java:6020) 
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105) 
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2259) 
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2366) 
at android.app.ActivityThread.access$800(ActivityThread.java:149) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1284) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:135) 
at android.app.ActivityThread.main(ActivityThread.java:5297) 
at java.lang.reflect.Method.invoke(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:372) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:908) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:703) 
Suppressed: java.lang.ClassNotFoundException: Didn't find class "com.stefan.example.MainActivity.CustomButton" on path: DexPathList[[dex file "/data/data/com.stefan.example/files/instant-run/dex/slice-support-annotations-24.1.1_6ce5cf7d8fc68e278012c1fdb63847d6984b1a82-classes.dex", dex file "/data/data/com.stefan.example/files/instant-run/dex/slice-slice_9-classes.dex", dex file "/data/data/com.stefan.example/files/instant-run/dex/slice-slice_8-classes.dex", dex file "/data/data/com.stefan.example/files/instant-run/dex/slice-slice_7-classes.dex", dex file "/data/data/com.stefan.example/files/instant-run/dex/slice-slice_6-classes.dex", dex file "/data/data/com.stefan.example/files/instant-run/dex/slice-slice_5-classes.dex", dex file "/data/data/com.stefan.example/files/instant-run/dex/slice-slice_4-classes.dex", dex file "/data/data/com.stefan.example/files/instant-run/dex/slice-slice_3-classes.dex", dex file "/data/data/com.stefan.example/files/instant-run/dex/slice-slice_2-classes.dex", dex file "/data/data/com.stefan.example/files/instant-run/dex/slice-slice_1-classes.dex", dex file "/data/data/com.stefan.example/files/instant-run/dex/slice-slice_0-classes.dex", dex file "/data/data/com.stefan.example/files/instant-run/dex/slice-internal_impl-24.1.1_d7334ac7335287759c12e17e515a73749d4ea418-classes.dex", dex file "/data/data/com.stefan.example/files/instant-run/dex/slice-com.android.support-support-vector-drawable-24.1.1_e21575ccf9da39363d36f579d76036b9825e0829-classes.dex





I've tried changing the xml file:

<Button
class = "com.stefan.example.MainActivity.CustomButton"
android:layout_width="match_parent"
android:layout_height="match_parent" />


It runs, but the view behaves like a normal button and my class is unused.

I've tried the app on different devices; all give the same exception.

Do I forget something? I hope I've just made a simple mistake.
Thank you in advance!

Answer

Either move your CustomButton class to the top level, or make it static. LayoutInflater fails to instantiate your class as it's a non-static inner class.

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