CODEWITHSUNDEEP
androidkotlinandroid-livedata
CB Midkiff
CB Midkiff

Reputation: 195

Questions about using 'liveData.observe'

I'm learning Android development on my own. I thought I had gotten my head around what/how 'liveData.observe' worked. But...

Making a small simple app that listens for input from a Bluetooth device and will display or hide an image based on that bluetooth input.

I have all that working, but now I want to add another feature and i'm running into a wall. The feature is to increase a counter each time the liveData.Observe returns TRUE.

Either I don't understand 'liveData.observe' or i'm trying to use it incorrectly(it is probably both of these things).

I'm working on a function now to increase this counter and this is the spot i'm getting hung up on. My current thinking is to create a seperate function(pigCounter()). But I'm getting nowhere.

onCreate

class MainActivity : AppCompatActivity() {
private var liveData: MutableLiveData<String> = MutableLiveData()

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

...
</SNIP>

liveData.observe(this, androidx.lifecycle.Observer {
        imageView_mothership_LED_state.showOrHideImage(it == "1")
    })

pigCounter()

}

Below is from activity_main.xml

imageView_mothership_LED_state

<ImageView
        android:id="@+id/imageView_mothership_LED_state"
        android:layout_width="124dp"
        android:layout_height="144dp"
        android:scaleType="fitCenter"
        android:soundEffectsEnabled="false"
        app:layout_constraintBottom_toBottomOf="@+id/imageView_blueYesOrNo"
        app:layout_constraintEnd_toEndOf="@+id/imageView_blueYesOrNo"
        app:layout_constraintStart_toStartOf="@+id/imageView_blueYesOrNo"
        app:layout_constraintTop_toTopOf="@+id/imageView_blueYesOrNo"
        app:srcCompat="@drawable/ic_check_black_24dp"
        android:contentDescription="Check mark image to indicate if LED is on/off" />

Below is the function that sets the images visibility

showOrHideImage()

// display or don't display check mark image
private fun View.showOrHideImage(imageShow: Boolean) {
    visibility = if (imageShow) View.VISIBLE else View.GONE
}

This is the function that handles the incoming bluetooth data.

readBlueToothDataFromMothership()

private fun readBlueToothDataFromMothership(bluetoothSocket: BluetoothSocket) {
    Log.i(LOGTAG, Thread.currentThread().name)
    val bluetoothSocketInputStream = bluetoothSocket.inputStream
    val buffer = ByteArray(1024)
    var bytes: Int
    //Loop to listen for received bluetooth messages
    while (true) {
        try {
            bytes = bluetoothSocketInputStream.read(buffer)
            val readMessage = String(buffer, 0, bytes)
            liveData.postValue(readMessage)
        } catch (e: IOException) {
            e.printStackTrace()
            break
        }
    }

This is the function i'm writing, in that I want to increase a counter each time.

pigCount

private fun pigCount() {
    var count = 0
    var counterTextView = findViewById<TextView>(R.id.textView_blueCounter)

    if(imageView_mothership_LED_state.showOrHideImage(true)) {
        counterTextView.text = count.toString()
        count++
    }

This does not work due to a type mismatch(expecting a Boolean, getting Unit). I've also tried moving this into the liveData.observe function up in onCreate(). But same road block.

Can anyone point me in the right direction. I have a sneaky feeling I am way off on this. And would appreicate a nudge. :)

Upvotes: 0

Views: 207

Answers (1)

Some random IT boy
Some random IT boy

Reputation: 8467

To count how many times a LiveData returns true it is really easy, you could just use a MediatorLiveData.

Assuming you have a proper LiveData<Boolean>, you could do as follows:

val trueFalse = MutableLiveData<Boolean>()

val counter by lazy {
     MediatorLiveData<Int>().apply {
          value = 0 // Initialize the counter
          // Add the trueFalse as a source of this live data
          addSource(trueFalse) { boolVal ->
              if(boolVal == true) {
                  // If the mediator live data had a value, use it, if null use 0; and add +1 to it because the boolVal was true
                  value = (value ?: 0) + 1
              }
          }
     }
}

/* Somewhere else in the code */
fun setupTextView() {
    counter.observe({lifecycle}) {
        val tv = findViewById<TextView>(R.id.tv_something)
        tv.text = "$it"
    }
}

This creates a MediatorLiveData that will have as a source the trueFalse live data. If the value is true will proceed and post a new value in the counter live data.

Upvotes: 1

Related Questions