CODEWITHSUNDEEP
androidkotlinandroid-intentandroid-activity
J Adonai Dagdag
J Adonai Dagdag

Reputation: 1945

Kotlin Android start new Activity

I want to start another activity on Android but I get this error:

Please specify constructor invocation; classifier 'Page2' does not have a companion object

after instantiating the Intent class. What should I do to correct the error? My code:

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }

    fun buTestUpdateText2 (view: View) {
        val changePage = Intent(this, Page2) 
        // Error: "Please specify constructor invocation; 
        // classifier 'Page2' does not have a companion object"

        startActivity(changePage)
    }

}

Upvotes: 150

Views: 258832

Answers (19)

Rahul
Rahul

Reputation: 10625

To start an Activity in java we wrote Intent(this, Page2.class), basically you have to define Context in first parameter and destination class in second parameter. According to Intent method in source code -

 public Intent(Context packageContext, Class<?> cls)

As you can see we have to pass Class<?> type in second parameter.

By writing Intent(this, Page2) we never specify we are going to pass class, we are trying to pass class type which is not acceptable.

Use ::class.java which is alternative of .class in kotlin. Use below code to start your Activity

Intent(this, Page2::class.java)

Example -

// start your activity by passing the intent
startActivity(Intent(this, Page2::class.java).apply {
    // you can add values(if any) to pass to the next class or avoid using `.apply`
    putExtra("keyIdentifier", value)
})

Upvotes: 247

AllanRibas
AllanRibas

Reputation: 1144

extension Functions

fun Activity.showToast(message: String, toastLength: Int){
    //LENGTH_SHORT = 0;
    //LENGTH_LONG = 1;
    Toast.makeText(this, message, toastLength).show()
}

fun Fragment.showToast(message: String, toastLength: Int){
    //LENGTH_SHORT = 0;
    //LENGTH_LONG = 1;
    Toast.makeText(requireContext(), message, toastLength).show()
}

fun Context.launchActivity(
    cls: Class<*>,
    flags: Int = 0,
    intentTransformer: Intent.() -> Unit = {}
) {
    val intent = Intent(this, cls).apply {
        addFlags(flags)
        intentTransformer()
    }
    this.startActivity(intent)
}

in an activity call

showToast("message to be shown", 1)

in a fragment call

showToast("message to be shown", 1)

start activity from any place

 launchActivity(MainActivity::class.java, Intent.FLAG_ACTIVITY_NEW_TASK)

Kotlin Extension function

Upvotes: 1

Prateek
Prateek

Reputation: 199

fun Context.launchActivity(
    cls: Class<*>,
    flags: Int = 0,
    intentTransformer: Intent.() -> Unit = {}
) {
    val intent = Intent(this, cls).apply {
        addFlags(flags)
        intentTransformer()
    }
    this.startActivity(intent)
}

Upvotes: 4

Mohamed AbdelraZek
Mohamed AbdelraZek

Reputation: 2809

another simple way of navigating to another activity is

Intent(this, CodeActivity::class.java).apply {
                    startActivity(this)
                }

Upvotes: 4

Gene
Gene

Reputation: 11267

You can use both Kotlin and Java files in your application.

To switch between the two files, make sure you give them unique < action android:name="" in AndroidManifest.xml, like so:

            <activity android:name=".MainActivityKotlin">
                <intent-filter>
                    <action android:name="com.genechuang.basicfirebaseproject.KotlinActivity"/>
                    <category android:name="android.intent.category.DEFAULT" />
                    <action android:name="android.intent.action.MAIN" />
                    <category android:name="android.intent.category.LAUNCHER" />
                </intent-filter>
            </activity>
            <activity
                android:name="com.genechuang.basicfirebaseproject.MainActivityJava"
                android:label="MainActivityJava" >
                <intent-filter>
                    <action android:name="com.genechuang.basicfirebaseproject.JavaActivity" />
                    <category android:name="android.intent.category.DEFAULT" />
                </intent-filter>
            </activity>

Then in your MainActivity.kt (Kotlin file), to start an Activity written in Java, do this:

       val intent = Intent("com.genechuang.basicfirebaseproject.JavaActivity")
        startActivity(intent)

In your MainActivityJava.java (Java file), to start an Activity written in Kotlin, do this: 

       Intent mIntent = new Intent("com.genechuang.basicfirebaseproject.KotlinActivity");
        startActivity(mIntent);

Upvotes: 0

libliboom
libliboom

Reputation: 551

How about this to consider encapsulation?

For example:


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_contents)

        val title = intent.getStringExtra(EXTRA_TITLE) ?: EXTRA_TITLE_DEFAULT

        supportFragmentManager.beginTransaction()
            .add(R.id.frame_layout_fragment, ContentsFragment.newInstance())
            .commit()
    }

    // Omit...

    companion object {

        private const val EXTRA_TITLE = "extra_title"
        private const val EXTRA_TITLE_DEFAULT = "No title"

        fun newIntent(context: Context, title: String): Intent {
            val intent = Intent(context, ContentsActivity::class.java)
            intent.putExtra(EXTRA_TITLE, title)
            return intent
        }
    }

Upvotes: 3

A S M Sayem
A S M Sayem

Reputation: 2070

Well, I found these 2 ways to be the simplest of all outcomes:

Way #1:

accoun_btn.setOnClickListener {
            startActivity(Intent(this@MainActivity, SecondActivity::class.java))
        }

Way#2: (In a generic way)

    accoun_btn.setOnClickListener {
        startActivity<SecondActivity>(this)
    }

    private inline fun <reified T> startActivity(context: Context) {
            startActivity(Intent(context, T::class.java))
        }

sample

Upvotes: 10

Gowtham Subramaniam
Gowtham Subramaniam

Reputation: 3478

Simply you can start an Activity in KOTLIN by using this simple method,

val intent = Intent(this, SecondActivity::class.java)
intent.putExtra("key", value)
startActivity(intent)

Upvotes: 63

Anton Makov
Anton Makov

Reputation: 845

I had a similar issue, I started to write my application in Kotlin, after I rewrote one of my activities I wanted to see if there are any issues, the problem was that I was not sure how to send an intent from java file to kotlin file.

In this case I created a static function in kotlin (companion object), this function is getting a context (from the current activity) and returning the new intent while using the current context ("java" context) while using the kotlin class ("::class.java").

Here is my code:

 //this code will be in the kotlin activity - SearchActivity
 companion object {

    fun newIntent(context: Context): Intent {
        return Intent(context, SearchActivity::class.java)
    }
}

    //this is how you call SearchActivity from MainActivity.java
Intent searchIntent = SearchActivity.Companion.newIntent(this);
startActivity(searchIntent);

Upvotes: 1

Ashish Patel
Ashish Patel

Reputation: 31

val intentAct: Intent = Intent(this@YourCurrentActivity, TagentActivity::class.java)
startActivity(intentAct)

Upvotes: 1

Nicolai Harbo
Nicolai Harbo

Reputation: 1169

Remember to add the activity you want to present, to your AndroidManifest.xml too :-) That was the issue for me.

Upvotes: 0

leoelstin
leoelstin

Reputation: 3258

To start a new Activity , 

startActivity(Intent(this@CurrentClassName,RequiredClassName::class.java)

So change your code to : 

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }

    fun buTestUpdateText2 (view: View) {
        startActivity(Intent(this@MainActivity,ClassName::class.java))

        // Also like this 

        val intent = Intent(this@MainActivity,ClassName::class.java)
        startActivity(intent)
    }

Upvotes: 38

Vasily Bodnarchuk
Vasily Bodnarchuk

Reputation: 25294

Details

  • Android Studio 3.1.4
  • Kotlin version: 1.2.60

Step 1. Application()

Get link to the context of you application 

class MY_APPLICATION_NAME: Application() {

    companion object {
        private lateinit var instance: MY_APPLICATION_NAME
        fun getAppContext(): Context = instance.applicationContext
    }

    override fun onCreate() {
        instance = this
        super.onCreate()
    }

}

Step 2. Add Router object

object Router {
    inline fun <reified T: Activity> start() {
         val context =  MY_APPLICATION_NAME.getAppContext()
         val intent = Intent(context, T::class.java)
         context.startActivity(intent)
    }
}

Usage

// You can start activity from any class: form Application, from any activity, from any fragment and other  
Router.start<ANY_ACTIVITY_CLASS>()

Upvotes: 0

EpicPandaForce
EpicPandaForce

Reputation: 81539

You can generally simplify the specification of the parameter BlahActivity::class.java by defining an inline reified generic function.

inline fun <reified T: Activity> Context.createIntent() =
    Intent(this, T::class.java)

Because that lets you do 

startActivity(createIntent<Page2>())

Or even simpler 

inline fun <reified T: Activity> Activity.startActivity() {
    startActivity(createIntent<T>()) 
}

So it's now 

startActivity<Page2>()

Upvotes: 16

Masum
Masum

Reputation: 4959

From activity to activity

val intent = Intent(this, YourActivity::class.java)
startActivity(intent)

From fragment to activity

val intent = Intent(activity, YourActivity::class.java)
startActivity(intent)

Upvotes: 5

Adib Faramarzi
Adib Faramarzi

Reputation: 4064

You have to give the second argument of class type. You can also have it a little bit more tidy like below. 

startActivity(Intent(this, Page2::class.java).apply {
    putExtra("extra_1", value1)
    putExtra("extra_2", value2)
    putExtra("extra_3", value3)
})

Upvotes: 16

Bharat Vasoya
Bharat Vasoya

Reputation: 361

This is my main activity where i take the username and password from edit text and setting to the intent

class MainActivity : AppCompatActivity() {
val userName = null
val password = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
button.setOnClickListener {
    val intent = Intent(this@MainActivity,SecondActivity::class.java);
    var userName = username.text.toString()
    var password = password_field.text.toString()
    intent.putExtra("Username", userName)
    intent.putExtra("Password", password)
    startActivity(intent);
 }
}

This is my second activity where i have to receive values from the main activity

override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_second)
var strUser: String = intent.getStringExtra("Username")
var strPassword: String = intent.getStringExtra("Password")
user_name.setText("Seelan")
passwor_print.setText("Seelan")
}

Upvotes: 8

Boris
Boris

Reputation: 368

Try this

val intent = Intent(this, Page2::class.java)
startActivity(intent)

Upvotes: 11

Alf Moh
Alf Moh

Reputation: 7427

This is because your Page2 class doesn't have a companion object which is similar to static in Java so to use your class. To pass your class as an argument to Intent, you will have to do something like this

val changePage = Intent(this, Page2::class.java)

Upvotes: 7

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