How to draw a line in android

Question

Can anybody tell how to draw a line in Android, perhaps with an example?

Amye

Answer 1

This one draws 2 lines which form a cross on the top left of the screen:

DrawView.java

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.View;

public class DrawView extends View {
    Paint paint = new Paint();

    private void init() {
        paint.setColor(Color.BLACK);
    }

    public DrawView(Context context) {
        super(context);
        init();
    }

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

    public DrawView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init();
    }

    @Override
    public void onDraw(Canvas canvas) {
            canvas.drawLine(0, 0, 20, 20, paint);
            canvas.drawLine(20, 0, 0, 20, paint);
    }

}

The activity to start it:

StartDraw.java

import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;

public class StartDraw extends Activity {
    DrawView drawView;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        drawView = new DrawView(this);
        drawView.setBackgroundColor(Color.WHITE);
        setContentView(drawView);

    }
}

Petuntse

if i want add a line in some other activity like R.layout.main How can i add? – Amye

the layout of your activity has to contain a View object - then it's no problem. You just need a View object to draw on – Petuntse

I want to draw a straight line how can i give the value startx start y stopx stopy? – Amye

actually you can find that in the android developer reference, drawLine() has the following arguments: drawLine(float startX, float startY, float stopX, float stopY, Paint paint) – Petuntse

I draw line on the background using this method. I want to erase a drawn line. Any suggestions for me. Can you suggest me? – Importunity

Answer 2

If you want to have a simple Line in your Layout to separate two views you can use a generic View with the height and width you want the line to have and a set background color.

With this approach you don't need to override a View or use a Canvas yourself just simple and clean add the line in xml.

<View
 android:layout_width="match_parent"
 android:layout_height="1dp"
 android:background="@android:color/black" />

The example code I provided will generate a line that fills the screen in width and has a height of one dp.

If you have problems with the drawing of the line on small screens consider to change the height of the line to px. The problem is that on a ldpi screen the line will be 0.75 pixel high. Sometimes this may result in a rounding that makes the line vanish. If this is a problem for your layout define the width of the line a ressource file and create a separate ressource file for small screens that sets the value to 1px instead of 1dp.

This approach is only usable if you want horizontal or vertical lines that are used to divide layout elements. If you want to achieve something like a cross that is drawn into an image my approach will not work.

Odoacer

How can add the same view at runtime that's dynamically? – Erickaericksen

Lakshmanan, give it an id, and set its visibility to View.GONE or VISIBLE at run-time – Unequal

A cross can also be made with this solution, just add "rotation" attribute in it as per the cross you want and use two views. – Denumerable

Answer 3

There are two main ways you can draw a line, by using a Canvas or by using a View.

Drawing a Line with Canvas

From the documentation we see that we need to use the following method:

drawLine (float startX, float startY, float stopX, float stopY, Paint paint)

Here is a picture:

The Paint object just tells Canvas what color to paint the line, how wide it should be, and so on.

Here is some sample code:

private Paint paint = new Paint();
....

private void init() {
    paint.setColor(Color.BLACK);
    paint.setStrokeWidth(1f);
}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    startX = 20;
    startY = 100;
    stopX = 140;
    stopY = 30;

    canvas.drawLine(startX, startY, stopX, stopY, paint);
}

Drawing a Line with View

If you only need a straight horizontal or vertical line, then the easiest way may be to just use a View in your xml layout file. You would do something like this:

<View
    android:layout_width="match_parent"
    android:layout_height="1dp"
    android:background="@android:color/black" />

Here is a picture with two lines (one horizontal and one vertical) to show what it would look like:

And here is the complete xml layout for that:

<?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" >

<TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="10dp"
    android:text="TextView1 in vertical linear layout" />

<View
    android:layout_width="match_parent"
    android:layout_height="1dp"
    android:background="@android:color/black" />

<TextView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:padding="10dp"
    android:text="TextView2 in vertical linear layout" />

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content" >

    <TextView
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:padding="10dp"
        android:text="TextView3 in horizontal linear layout" />

    <View
        android:layout_width="1dp"
        android:layout_height="match_parent"
        android:background="@android:color/black" />

    <TextView
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:padding="10dp"
        android:text="TextView4 in horizontal linear layout" />
</LinearLayout>

</LinearLayout>

Canula

you are a genius bro... I have been trying to figure out how they get the coordinates while drawing a view using paint...but the picture that you've posted helped me to understand it pretty much.... Is there any online tool to simulate such graph so i use it while coding? – Teachin

is it possible to get a callback to know that the view has been finished drawing – Teachin

Im trying to draw two different lines. Once if the first line has been drawn, i have to draw the second... – Teachin

Why don't you draw both lines in the same onDraw? – Canula

I draw line on the background using this method. I want to erase a drawn line. Any suggestions for me. Can you suggest me? – Importunity

@tientuyen07, If you are using onDraw() then surround your drawing code with if (someCondition) { draw... }, make someCondition = false, and then call invalidate() on your view. It will redraw the view without the line. – Canula

Answer 4

You can draw multiple straight lines on view using Finger paint example which is in Developer android. example link

Just comment: mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2); You will be able to draw straight lines.

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.Point;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.ImageView;

public class JoinPointsActivity extends Activity  {
    /** Called when the activity is first created. */
    Paint mPaint;
    float Mx1,My1;
    float x,y;
    @Override

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
       // setContentView(R.layout.main);
        MyView view1 =new MyView(this);
        view1.setBackgroundResource(R.drawable.image_0031_layer_1);
        setContentView(view1);


        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setColor(0xFFFF0000);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
       // mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(10);

    }

    public class MyView extends View {

        private static final float MINP = 0.25f;
        private static final float MAXP = 0.75f;

      private Bitmap  mBitmap;
        private Canvas  mCanvas;
        private Path    mPath;
       private Paint   mBitmapPaint;

        public MyView(Context c) {
            super(c);

            mPath = new Path();
          mBitmapPaint = new Paint(Paint.DITHER_FLAG);
        }

        @Override
       protected void onSizeChanged(int w, int h, int oldw, int oldh) {
            super.onSizeChanged(w, h, oldw, oldh);
            mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
            mCanvas = new Canvas(mBitmap);
        }

        @Override
        protected void onDraw(Canvas canvas) {
            canvas.drawColor(0xFFAAAAAA);
           // canvas.drawLine(mX, mY, Mx1, My1, mPaint);
           // canvas.drawLine(mX, mY, x, y, mPaint);
            canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
            canvas.drawPath(mPath, mPaint);

        }

        private float mX, mY;
        private static final float TOUCH_TOLERANCE = 4;

        private void touch_start(float x, float y) {
            mPath.reset();
            mPath.moveTo(x, y);
            mX = x;
            mY = y;
        }
        private void touch_move(float x, float y) {
            float dx = Math.abs(x - mX);
            float dy = Math.abs(y - mY);
            if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
               // mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
                mX = x;
                mY = y;
            }
        }
        private void touch_up() {
            mPath.lineTo(mX, mY);
            // commit the path to our offscreen
            mCanvas.drawPath(mPath, mPaint);
            // kill this so we don't double draw
            mPath.reset();
        }

        @Override
        public boolean onTouchEvent(MotionEvent event) {
            float x = event.getX();
            float y = event.getY();

            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    touch_start(x, y);
                    invalidate();
                    break;
                case MotionEvent.ACTION_MOVE:
                    touch_move(x, y);
                    invalidate();
                    break;
                case MotionEvent.ACTION_UP:
                    touch_up();
               //   Mx1=(int) event.getX();
                 //  My1= (int) event.getY();
                   invalidate();
                    break;
            }
            return true;
        }
    }

}

Milburr

Can Someone help me how can i see my xml elements on my view which are on relative layout?? u can just go through the above example and suggest me. – Milburr

Answer 5

package com.example.helloandroid;

import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.view.View;

public class HelloAndroid2Activity extends Activity {
    /** Called when the activity is first created. */
DrawView drawView;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    drawView = new DrawView(this);
    drawView.setBackgroundColor(Color.WHITE);
    setContentView(drawView);
}
class DrawView extends View {
        Paint paint = new Paint();

        public DrawView(Context context) {
            super(context);
            paint.setColor(Color.BLUE);
        }
        @Override
        public void onDraw(Canvas canvas) {
             super.onDraw(canvas);
                canvas.drawLine(10, 20, 30, 40, paint);
                canvas.drawLine(20, 10, 50, 20, paint);

        }
}
}

Bisayas

Answer 6

Simple one

 <TextView
    android:layout_width="match_parent"
    android:layout_height="1dp"
    android:background="#c0c0c0"
    android:id="@+id/your_id"
    android:layout_marginTop="160dp" />

Womanlike

Answer 7

for horizontal line on the layout :

 <View
            android:id="@+id/View03"
            android:layout_width="fill_parent"
            android:layout_height="5dip"
            android:background="#0f0" />

for vertical line on the layout :

<View
        android:id="@+id/View04"
        android:layout_width="5dip"
        android:layout_height="fill_parent"
        android:background="#0f0" />

Dyspnea

they are both same. what makes the difference between vertical and horizontal? – Langtry

@ Burhan ARAS-they are not same as width and height are changed in two views.it draws only vertical and horz line. – Dyspnea

Answer 8

canvas.drawLine(10, 10, 90, 10, paint);
canvas.drawLine(10, 20, 90, 20, paint);

This will create a straight horizontal line, hope it helps!.

Nitrosamine

Answer 9

You can make a drawable like circle, line, rectangle etc through shapes in xml as follow:

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" 
    android:shape="line" >

    <solid android:color="#00000000" />

    <stroke
        android:width="2dp"
        android:color="#808080" />

</shape>

Auramine

Answer 10

this code adds horizontal line to a linear layout

View view = new View(this);
LinearLayout.LayoutParams lpView = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, 1); // --> horizontal
view.setLayoutParams(lpView);
view.setBackgroundColor(Color.DKGRAY);

linearLayout.addView(view);

Mccain

Answer 11

If you're working with ConstraintLayout you need to define at least 2 constraints for the line to show up. Like this:

<View
        android:layout_width="0dp"
        android:layout_height="1dp"
        android:background="@android:color/black"
        app:layout_constraintEnd_toEndOf="@+id/someView1"
        app:layout_constraintStart_toStartOf="@+id/someView2"
        app:layout_constraintTop_toBottomOf="@+id/someView3" />

Though I defined 3 constraints.

Kinross

Answer 12

If anyone can benefit from a simplified solution:

Point class not needed. Directly in MotionEvent.ACTION_MOVE move to the start X and Y coordinates that you get from MotionEvent.ACTION_DOWN. This method works better since we use drawPath instead of drawLine, which is less computationally intensive and therefore performs better.

class DrawingView(context: Context,
                  attributeSet: AttributeSet): View(context, attributeSet) {

    private val mPaint = Paint()
    private var mPath = Path()
    var startX = 0f
    var startY = 0f
    var endX = 0f
    var endY = 0f
    init {
        mPaint.color = Color.GREEN
        mPaint.style = Paint.Style.STROKE
        mPaint.strokeJoin = Paint.Join.ROUND
        mPaint.strokeCap = Paint.Cap.ROUND
        mPaint.strokeWidth = 50f

    }
    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)
        canvas.drawPath(mPath, mPaint)
    }

    override fun onTouchEvent(event: MotionEvent): Boolean {
       when (event.action) {
            MotionEvent.ACTION_DOWN -> {
                startX = event.x
                startY = event.y
                invalidate()
            }
            MotionEvent.ACTION_MOVE -> {
                endX = event.x
                endY = event.y
                val path = Path()
                path.moveTo(startX, startY) <- // Important!
                path.lineTo(endX, endY)
                mPath = path
                invalidate()
            }
        }
        return true
    }
}

Bawl

Answer 13

  final SurfaceView surf = (SurfaceView)findViewById(R.id.surface_home);
                surf.setOnTouchListener( new SurfaceView.OnTouchListener(){
                    private boolean moving = false;//stupid state
                    public boolean onTouch(View v, MotionEvent event) {
                        switch( event.getAction() ){
                        case MotionEvent.ACTION_DOWN:
                            final int x = (int)event.getX();
                            final int y = (int)event.getY();
                            final Rect bounds = mTiles.getBounds();
                            moving = bounds.intersects(x, y, x+1, y+1);
                            return true;
                        case MotionEvent.ACTION_MOVE:
                            if( moving ){
                                final int x_new = (int)event.getX();
                                final int y_new = (int)event.getY();
                                mDrawTiles.draw( new DrawLogic(){
                                    public void draw(Rect _surface) {
                                        mTiles.setBounds(
                                            x_new - mDrawWidth/2,
                                            y_new - mDrawHeight/2,
                                            x_new + mDrawWidth/2,
                                            y_new + mDrawHeight/2);
                                        }
                                    });

Peruzzi

Answer 14

To improve on the answers provided by @Janusz

I added this to my styles:

<style name="Divider">
    <item name="android:layout_width">match_parent</item>
    <item name="android:layout_height">1dp</item>
    <item name="android:background">?android:attr/listDivider</item>
</style>

Then in my layouts is less code and simpler to read.

<View style="@style/Divider"/>

if you want to do horizontal line spacing then do the above.

---

And for vertical line between two Views you have to replace android:layout_width parameters(attributes) with android:layout_height

Collencollenchyma

Answer 15

Another approach to draw a line programatically using ImageView

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.Typeface;
import android.os.Bundle;
import android.widget.ImageView;

public class Test extends Activity {
  ImageView drawingImageView;

  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    drawingImageView = (ImageView) this.findViewById(R.id.DrawingImageView);
    Bitmap bitmap = Bitmap.createBitmap((int) getWindowManager()
        .getDefaultDisplay().getWidth(), (int) getWindowManager()
        .getDefaultDisplay().getHeight(), Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(bitmap);
    drawingImageView.setImageBitmap(bitmap);

    // Line
    Paint paint = new Paint();
    paint.setColor(Color.GREEN);
    paint.setStrokeWidth(10);
    int startx = 50;
    int starty = 100;
    int endx = 150;
    int endy = 210;
    canvas.drawLine(startx, starty, endx, endy, paint);

  }
}

Collencollenchyma

Answer 16

or if you just want a line

TextView line = new TextView(this);
            line.setBackgroundResource(android.R.color.holo_red_dark);
            line.setHeight((int) Utility.convertDpToPixel(1,this));

Galiot