CODEWITHSUNDEEP
androidkotlinandroid-canvassurfaceview
Cindy9
Cindy9

Reputation: 1

Drawing a Line on SurfaceView

When I press the button and try to draw a yellow line on SurfaceView, some random mess appears on the screen. How can I access the phone screen the fastest possible way properly to draw lines, rectangles and other basic shapes on it in the app?

I use the code

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/mylinearlayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    >
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="MY BUTTON"
        android:id="@+id/mybutton"
        />
    <SurfaceView
        android:id="@+id/mysurfaceview"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        tools:context=".MainActivity"/>
</LinearLayout>

and

package com.example.myapp

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import android.graphics.Color
import android.graphics.Paint
import android.view.SurfaceView
import android.widget.Button

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val sv=findViewById<SurfaceView>(R.id.mysurfaceview)
        val b=findViewById<Button>(R.id.mybutton)
        b.setOnClickListener() {
            val mycanvas=sv.holder.lockCanvas()
            val mypaint= Paint()
            mypaint.setColor(Color.YELLOW)
            mypaint.isAntiAlias=true
            mypaint.strokeWidth=5f
            mypaint.style=Paint.Style.FILL
            mycanvas.drawLine(20f,20f,450f,520f,mypaint)
            sv.holder.unlockCanvasAndPost(mycanvas)
        }
    }
}

which produces this:

screenshot

Upvotes: 0

Views: 28

Answers (1)

dev.bmax
dev.bmax

Reputation: 10621

You should clear the canvas before drawing.

Either make the background transparent:

mycanvas.drawColor(Color.TRANSPARENT, PorterDuff.Mode.CLEAR)

or use solid color:

mycanvas.drawColor(Color.WHITE)

There is another issue in your code - you are not handling the Surface lifecycle events as described in the docs. This can cause crashes. Consider implementing a custom view class.

Upvotes: 0

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