canvas not drawing in java android

问题:

I think the code is right, but I'm unable to find what's going wrong. Can anyone help please in figuring out what's incorrect ?

Thats the activity document:

package com.example.crazyeights;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;

public class CrazyEightsActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        MyView view = new MyView(this);
        setContentView(view);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.crazy_eights, menu);
        return true;
    }

}

thats what i want to display in the screen:

package com.example.crazyeights;
import android.content.Context; 
import android.view.View;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;

public class MyView extends View{

    private Paint redPaint;
    private int circleX;
    private int circleY;
    private float radius;

    public MyView(Context context) {
        super(context);
        redPaint = new Paint();
        redPaint.setAntiAlias(true);
        redPaint.setColor(Color.RED);
        circleX = 100;
        circleY = 100;
        radius = 30;
    }
    protected void OnDraw(Canvas canvas){
             canvas.drawCircle(circleX, circleY, radius, redPaint);
    }
}

回答1:

The uppercase OnDraw() method you specified will not be called that way. You actually need to override the onDraw() method when using a custom view, e.g:

@Override
protected void onDraw(Canvas canvas) {
    canvas.drawCircle(circleX, circleY, radius, redPaint);
}

I tested it and that draws a red circle. See documentation on Custom Drawing here, specifically the Override onDraw() section.

回答2:

have you tried to add, in your constructor redPaint.setStyle(...) for example:

redPaint.setStyle(Paint.Style.FILL) redpaint.setStyle(Paint.Style.STROKE);