在畫布(Canvas)上繪畫圖形

這是一個自定義視圖(custom view)的簡單例子, 說明如何在畫布(Canvas)上繪畫圖形.



創建一個自定義的視圖類, MyCanvas.java

package com.AndroidCanvasDraw;

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

public class MyCanvas extends View {

private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
int canvasVerticalCenter;

public MyCanvas(Context context) {
 super(context);
 // TODO Auto-generated constructor stub
 init();
}

public MyCanvas(Context context, AttributeSet attrs) {
 super(context, attrs);
 // TODO Auto-generated constructor stub
 init();
}

public MyCanvas(Context context, AttributeSet attrs, int defStyle) {
 super(context, attrs, defStyle);
 // TODO Auto-generated constructor stub
 init();
}

private void init(){
 paint.setStyle(Paint.Style.FILL);
 paint.setStrokeWidth(1);
 paint.setColor(Color.WHITE);
}

@Override
protected void onDraw(Canvas canvas) {
 // TODO Auto-generated method stub
 prepareProject();
 for(int i = 0; i < getWidth(); i++){
  int value = (int)(Math.sin(Math.toRadians(i))*100);
  project(i, value, canvas);
 }
}

void prepareProject(){
 canvasVerticalCenter = getHeight()/2;
}

void project(int x, int y, Canvas c){
 c.drawLine(x, canvasVerticalCenter, x, canvasVerticalCenter-y, paint);
 //c.drawPoint(x, canvasVerticalCenter-y, paint);
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
 // TODO Auto-generated method stub
 setMeasuredDimension(MeasureSpec.getSize(widthMeasureSpec),
   MeasureSpec.getSize(heightMeasureSpec));
}

}

在主代碼調用使用 MyCanvas 類.

package com.AndroidCanvasDraw;

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

public class AndroidCanvasDraw extends Activity {
   /** Called when the activity is first created. */
   @Override
   public void onCreate(Bundle savedInstanceState) {
       super.onCreate(savedInstanceState);
       MyCanvas myCanvas = new MyCanvas(this);
       setContentView(myCanvas);
   }
}

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