Draw a Line with a Java class Android

Question

I´m new to Android(Java). I want to draw a Line with this:

public void drawAline(int x1,int y1, int x2, int y2){
        Canvas canvas=new Canvas();
        paint.setColor(Color.BLACK);
        canvas.drawLine(x1,y1,x2,y2,paint);
    }

paint.setColor is working but its not drawing the line:

Call:

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        drawView = new DrawView(this);
        drawView.setBackgroundColor(Color.RED);
        drawView.drawAline(0,10,1000,10);

        setContentView(drawView);

What is the problem?

Thanks!

Kind regards

Daniel

`drawAline` creates a `Canvas` and draws over it, but where is this `Canvas` displayed ? — Arnaud, Mar 22 '16 at 10:21
You will have to ovverride `onDraw` of your view , like in this example : http://stackoverflow.com/questions/26727753/how-to-save-canvas-drawing-and-display-it-when-the-button-is-clicked — Arnaud, Mar 22 '16 at 10:27

score 2 · Accepted Answer · answered Mar 22 '16 at 10:38

draw a line then use this code to draw line simply

public class MainActivity extends Activity {

DrawLine drawLine;

@Override
public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    drawLine = new DrawLine(this);

    drawLine.setBackgroundColor(Color.CYAN);

    setContentView(drawLine);
  }

    class DrawLine extends View {
        Paint paint = new Paint();
        public DrawLine(Context context) {
            super(context);
            paint.setColor(Color.BLACK);
        }

        @Override
        public void onDraw(Canvas canvas) {
            canvas.drawLine(50, 100, 600, 600, paint);
            canvas.drawLine(50, 550, 770, 0, paint);
        }

    }
}

Sumanth Jois · Answer 2 · 2016-03-22T10:46:46.493

You cannot do it like you are trying to do. basically in android every view i.e buttons or images or EditText are defined in xml files which will be wired to your java file(You can also define view in your java file). In your case, if you want to draw a line , for example considering the line as a image. You can do it like the below.

1) First Create a class which extends ImageView and override onDraw() method.

2)then define the view in your xml file

Java class

 package com.stack.line;
    public class CustomView extends View {
        Paint paint = new Paint();
        public CustomImageView(Context context) {
            super(context);
               paint.setAntiAlias(true);
            paint.setColor(Color.RED);
        }

        @Override
        public void onDraw(Canvas canvas) {
            canvas.drawLine(10, 100, 150, 300, paint);

        }

    }

custom_view.xml File

<LinearLayout

    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"



    >

<com.stack.line.CustomView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/custom"

    />

</LinearLayout>

MainActivity.java

public class MainActivity extends Activity{
  @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.custom_view);

}
}

Hope this was helpful. ThankYou

Draw a Line with a Java class Android

2 Answers2