Develop Reference

Does View::invalidate redraw ervery child View?

I thought android had a diff mechanism to avoid redraw whole View tree when I invoke View::invalidate. Through checking the source code of View::invalidate, I find the invalidate
will propagate to ViewRootImpl and invoke ViewRootImpl::performTraversals. This method then draw whole view tree(except hardware acceleration enabled).
I try to find the code that View/ViewGroup can skip draw accroding dirty region, But I failed.Seems like erevry view will invoke onDraw
Below case, why does #id/frame_layout invoke onDraw when I change child #id/front backgroud color? Should't it refresh view locally?
layou.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:theme="#style/Theme.AppCompat.NoActionBar"
tools:context=".MainActivity">
<FrameLayout
android:id="#+id/frame_container"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintBottom_toBottomOf="#id/btn"
android:layout_width="match_parent"
android:layout_height="match_parent">
<FrameLayout
android:id="#+id/layout_back"
android:background="#color/black"
android:layout_width="100dp"
android:layout_height="100dp"
/>
<FrameLayout
android:id="#+id/layout_front"
android:background="#color/white"
android:layout_width="100dp"
android:layout_height="100dp"
/>
</FrameLayout>
<com.google.android.material.button.MaterialButton
android:id="#+id/btn"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="switch color"
app:layout_constraintBottom_toBottomOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
package com.flybutter.demo
import android.graphics.Color
import android.os.*
import android.util.Log
import android.view.View
import androidx.appcompat.app.AppCompatActivity
import android.widget.Toast
import androidx.lifecycle.LifecycleObserver
import com.bumptech.glide.Glide
import com.flybutter.demo.databinding.ActivityMainBinding
private const val TAG = "MainActivity"
class MainActivity : AppCompatActivity() {
lateinit var binding: ActivityMainBinding
var c = false
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
binding = ActivityMainBinding.inflate(layoutInflater)
binding.frameLayout.viewTreeObserver.addOnDrawListener {
Log.d(TAG, "onCreate: container ondraw")
}
binding.layoutFront.viewTreeObserver.addOnDrawListener {
Log.d(TAG, "onCreate: front on draw")
}
binding.layoutFront.viewTreeObserver.addOnDrawListener {
Log.d(TAG, "onCreate: back on draw")
Log.d(TAG,">>>>>>>>>>>>>>>>>>>")
}
binding.btn.setOnClickListener {
binding.layoutFront.setBackgroundColor( if (c) Color.WHITE else Color.GRAY)
c = !c
}
setContentView(binding.root)
}
}

Changing text value with Kotlin in Android Studio

New to Kotlin, I've followed the guide on how to set up a basic "Press the button and it changes text" However Whenever I press the button, the app crashes and in the debugger I get
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)'
on a null object reference at com.example.myapplication.MainActivity.One(MainActivity.kt:16)
Here is my current MainActivity.KT:
package com.example.myapplication
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.TextView
import kotlinx.android.synthetic.main.activity_main.*
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
fun One(view: android.view.View) {
val onetext = view.findViewById<TextView>(R.id.textView)
onetext.text = "Hello"
}
}
And my activity_main.xml:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<TextView
android:id="#+id/textView"
android:layout_width="168dp"
android:layout_height="90dp"
android:text="Hello World!"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<Button
android:id="#+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="One"
android:text="Button"
tools:layout_editor_absoluteX="163dp"
tools:layout_editor_absoluteY="462dp" />
</androidx.constraintlayout.widget.ConstraintLayout>
Thank you!

The problem is onetext is null, which means view.findViewById<TextView>(R.id.textView) didn't find a view with textView as id inside of view. The view passed in the function is the button, which has no textView as a child. You need to search for the textView in a view higher in the hierarchy.
In the specific example, one way of doing that is by omitting the view receiver, like so:
package com.example.myapplication
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.TextView
import kotlinx.android.synthetic.main.activity_main.*
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
fun One(view: android.view.View) {
val onetext = findViewById<TextView>(R.id.textView)
onetext.text = "Hello"
}
}
This way it will search for the textView id in the Activity's view, which is the activity_main layout.

I believe the problem has already been solved, but I noticed that in the xml file the button is not properly docked, putting:
app:layout_constraintTop_toBottomOf="#id/textView"
the button would be below the TextView component and putting:
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
the button would be centered on the screen...
Button code would look like this
<Button
android:id="#+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onClick="One"
android:text="Button"
app:layout_constraintTop_toBottomOf="#id/textView"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"/>

Android Button setOnClickListener call function to change button image

I have an app with multiple buttons and the image will change depending on different requirements and variables. But, I cannot get the image button change to work within the function. The setOnClickListner will setup the function call and within the function will change the image within the button.
How do I change the image in the button?
MainActivity.kt
package com.example.sandpit9
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import kotlinx.android.synthetic.main.activity_main.*
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
imageButton1.setOnClickListener() { changeimageelement1(R.drawable.button) }
imageButton2.setOnClickListener() { changeimageelement2(R.drawable.button) }
}
}
private fun changeimageelement1(imageButtonX: Int) {
imageButton1.setImageResource(R.drawable.greenbutton)
}
MainActivity.xml
<?xml version="1.0" encoding="utf-8">
<android.support.constraint.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<ImageButton
android:layout_width="174dp"
android:layout_height="154dp" app:srcCompat="#drawable/download"
android:id="#+id/imageButton1"
app:layout_constraintEnd_toEndOf="parent" android:layout_marginEnd="8dp" android:layout_marginRight="8dp"
app:layout_constraintStart_toStartOf="parent" android:layout_marginLeft="8dp"
android:layout_marginStart="8dp" android:layout_marginTop="8dp" app:layout_constraintTop_toTopOf="parent"
android:layout_marginBottom="8dp" app:layout_constraintBottom_toBottomOf="parent"/> .
</android.support.constraint.ConstraintLayout>

you should not use the () after setOnClickListener, just use
button.setOnClickLisener{
//your actions go here
}

ClickListener method should besetOnClickListener not setOnClickListener
A sample code:
button.setOnClickListener{
counter++
textView.text = "Click counter : $counter"
}
Check this tutorial

Kotlin extension view binding : "Overload resolution ambiguity.." error on editor on custom button

I am using the new kotlin extension for view binding but I am having this annoying warning red underline message custom_button.setOnClickListener{} stating "Overload resolution ambiguity.."
I am trying to use my custom button class which extends Button class.
My activity class
package com.example.myapplication
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import kotlinx.android.synthetic.main.activity_main.*
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
custom_button.setOnClickListener { }
}
}
Custom button class
package com.example.myapplication
import android.content.Context
import android.widget.Button
class CustomButton(context: Context?) : Button(context)
XML
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<com.example.myapplication.CustomButton
android:id="#+id/custom_button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>

How to replace a FrameLayout with a fragment with Kotlin on Android

I'm trying to develop an Android app with Kotlin, but I've hit a bit of a snag when trying to dynamically move fragments around. What I'm trying to do is replace a FrameLayout in an Activity's layout with a fragment. Currently whenever I try to run my app it just shows a white screen under the toolbar leading me to believe that the fragment is not being added to the FrameLayout the way I expected.
Here is my main Activity where I do the first transaction:
package net.ma.ttrobinson.kchan
import android.content.Intent
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.support.v7.widget.Toolbar
import android.util.Log
import android.view.Menu
import android.view.MenuItem
import android.view.View
import android.widget.Button
import android.widget.EditText
import com.androidquery.callback.AjaxStatus
import net.ma.ttrobinson.kchan.api.ChanThread
import net.ma.ttrobinson.kchan.api.Request
import org.jdeferred.DoneCallback
import org.jdeferred.FailCallback
import org.json.JSONArray
import org.json.JSONObject
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val toolbar = findViewById(R.id.toolbar) as Toolbar
setSupportActionBar(toolbar)
getSupportFragmentManager().beginTransaction()
.replace(R.id.main_content_frame, MainFragment())
.commit()
}
}
Here is the fragment I'm attempting to create. It simply inflates a view while adding a callback for when a button is pressed:
package net.ma.ttrobinson.kchan
import android.os.Bundle
import android.support.v4.app.Fragment
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Button
import android.widget.EditText
import com.androidquery.callback.AjaxStatus
import net.ma.ttrobinson.kchan.api.ChanThread
import net.ma.ttrobinson.kchan.api.Request
import org.jdeferred.DoneCallback
import org.jdeferred.FailCallback
/**
* Holds the main content
*/
class MainFragment : Fragment() {
companion object {
val TAG = "MainFragment"
}
val debugBoard = "g"
val debugThread = "48667796"
override fun onCreateView(inflater : LayoutInflater, parent : ViewGroup?, savedInstanceState : Bundle?) : View {
val v = inflater.inflate(R.layout.fragment_main, parent, false)
val boardText = v.findViewById(R.id.board_text) as EditText
val threadText = v.findViewById(R.id.thread_text) as EditText
val request = Request(getActivity())
boardText.setText(debugBoard)
threadText.setText(debugThread)
val button = v.findViewById(R.id.submit) as Button
button.setOnClickListener({ v ->
val board = boardText.getText().toString()
val thread = threadText.getText().toString().toInt()
val promise = request.getThread(board, thread)
promise.done({ thread ->
val fm = getActivity().getSupportFragmentManager()
fm.beginTransaction()
.replace(R.id.main_content_frame, ThreadFragment(thread), ThreadFragment.TAG)
.addToBackStack(null)
.commit()
}).fail({ result ->
Log.v(TAG, "Failed to get thread")
})
})
return v
}
}
Here's the layout that the main Activity uses with setContentView:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<include
android:id="#+id/toolbar"
layout="#layout/toolbar" />
<FrameLayout
android:id="#+id/main_content_frame"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
And lastly here's the layout that the fragment is inflating:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<EditText
android:id="#+id/board_text"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:hint="#string/board_hint"/>
<EditText
android:id="#+id/thread_text"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:inputType="phone"
android:hint="#string/thread_hint"/>
<Button
android:id="#+id/submit"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="#string/submit"/>
</LinearLayout>
I feel like this is a fairly straightforward setup of a main Activity that has a FrameLayout that can be swapped out with other fragments. Does anyone know what I might be doing wrong?
In the meantime I suppose I'll try to make a simpler case to try to replicate the behaviour.
EDIT: Such a simple solution. I forgot to add android:orientation="vertical" in my LinearLayout. Here's the updated code:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<include
android:id="#+id/toolbar"
layout="#layout/toolbar" />
<FrameLayout
android:id="#+id/main_content_frame"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>

The problem is that the Activity's LinearLayout should have orientation="vertical":
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<include
android:id="#+id/toolbar"
layout="#layout/toolbar" />
<FrameLayout
android:id="#+id/main_content_frame"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>

Just i want to pay your intention to extension function it's so useful.
Here i will share some steps to do that
Creat a kotlin file called util for example and add those function which allow to add and replace the fragment
util.kt
fun AppCompatActivity.addFragment(fragment: Fragment, frameId: Int){
supportFragmentManager.inTransaction { add(frameId, fragment) }
}
fun AppCompatActivity.replaceFragment(fragment: Fragment, frameId: Int) {
supportFragmentManager.inTransaction{replace(frameId, fragment)}
}
inline fun FragmentManager.inTransaction(func: FragmentTransaction.() -> FragmentTransaction) {
beginTransaction().func().commit()
}
Create your fragment layout. I have call it father_fragment for example
fahter_fragment
<!-- You can put whatever you want here-->
In your Activity xml create a layout which will caontain the fragment:
activity_principal.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 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"
tools:context="com.tharwa.tdm2_exo2.Principal">
<FrameLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/container"
>
</FrameLayout>
</android.support.design.widget.CoordinatorLayout>
Now in youe activity you can easily create the fragment
Principal
class Principal : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_principal)
//Create and add the fragment
val fatherView=FatherPresentation()
addFragment(fatherView,R.id.container)
}
}
if you want to replace the fragment from your activity it's easy just do
replaceFragment(Fragment_you_want_to_replace_with(),id_of_of_your_frame_layout)