How to draw a line in android


Question

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

1
147
11/4/2011 1:16:07 AM

Accepted Answer

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);

    }
}
167
8/10/2017 9:56:16 AM

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.


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