I am making an app that displays a speed dial but whenever I run the app, I get the message
java.lang.InstantiationException: can't instantiate class : no empty constructor
How do I fix this?
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.RadialGradient;
import android.graphics.Shader;
import android.util.AttributeSet;
import android.view.View;
public class Needle extends View {
private Paint linePaint;
private Path linePath;
private Paint needleScrewPaint;
private Matrix matrix;
private int framePerSeconds = 100;
private long animationDuration = 10000;
private long startTime;
public Needle(Context context) {
super(context);
matrix = new Matrix();
this.startTime = System.currentTimeMillis();
this.postInvalidate();
init();
}
public Needle(Context context, AttributeSet attrs) {
super(context, attrs);
matrix = new Matrix();
this.startTime = System.currentTimeMillis();
this.postInvalidate();
init();
}
public Needle(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
matrix = new Matrix();
this.startTime = System.currentTimeMillis();
this.postInvalidate();
init();
}
private void init(){
linePaint = new Paint();
linePaint.setColor(Color.RED); // Set the color
linePaint.setStyle(Paint.Style.FILL_AND_STROKE); // set the border and fills the inside of needle
linePaint.setAntiAlias(true);
linePaint.setStrokeWidth(5.0f); // width of the border
linePaint.setShadowLayer(8.0f, 0.1f, 0.1f, Color.GRAY); // Shadow of the needle
linePath = new Path();
linePath.moveTo(50.0f, 50.0f);
linePath.lineTo(130.0f, 40.0f);
linePath.lineTo(600.0f, 50.0f);
linePath.lineTo(130.0f, 60.0f);
linePath.lineTo(50.0f, 50.0f);
linePath.addCircle(130.0f, 50.0f, 20.0f, Path.Direction.CW);
linePath.close();
needleScrewPaint = new Paint();
needleScrewPaint.setColor(Color.BLACK);
needleScrewPaint.setAntiAlias(true);
needleScrewPaint.setShader(new RadialGradient(130.0f, 50.0f, 10.0f,
Color.DKGRAY, Color.BLACK, Shader.TileMode.CLAMP));
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
long elapsedTime = System.currentTimeMillis() - startTime;
matrix.postRotate(1.0f, 130.0f, 50.0f); // rotate 10 degree every second
canvas.concat(matrix);
canvas.drawPath(linePath, linePaint);
canvas.drawCircle(130.0f, 50.0f, 16.0f, needleScrewPaint);
if(elapsedTime < animationDuration){
this.postInvalidateDelayed(10000 / framePerSeconds);
}
//this.postInvalidateOnAnimation();
invalidate();
}
}
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{needle.ibizsmart.com.needle/com.needle.views.Needle}: java.lang.InstantiationException: can't instantiate class com.needle.views.Needle; no empty constructor
Somewhere in your manifest, you have an <activity>
element that indicates that com.needle.views.Needle
is a subclass of Activity
.
And, somewhere in your Java code, you are calling startActivity()
, with an Intent
that points to com.needle.views.Needle
.
However, com.needle.views.Needle
does not inherit from Activity
. It inherits from View
. You cannot use it as an activity.
You are certainly welcome to create a different class that does inherit from Activity
, that uses Needle
as part of its user interface.
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