android -> canvas learning 2 (dynamic drawing)

 

The keyword   invalidate() re-executes onDraw() , the following example moves the screen horizontally down a bit each time the screen is clicked

 

package com.test1;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

/**
 * Jiugongge unlock controls
 * Created by Jerry on 2015/9/21.
 */
public class DiyView extends View {
    public DiyView(Context context) {
        this(context, null);
    }
    public DiyView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }
    public DiyView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    int y = 0;

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

        // create a new brush
        Paint paint = new Paint();
        paint.setColor(Color.parseColor("#00B7EE"));
        paint.setAntiAlias(true);//Anti-aliasing
        paint.setStrokeWidth(33);
        // draw a straight line
        //drawLine(float startX, float startY, float stopX, float stopY,Paint)
        canvas.drawLine(30,y,500,y,paint);

        print("draw");
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        if(event.getAction() == MotionEvent.ACTION_UP){
            y+=10;
            invalidate();//Re-execute onDraw
        }

        return true;
    }

    public void print(String str){
        Log.d("mft",str);
    }
}