Android 程式 -- 手寫繪圖板

程式範例：DrawBoard.java

package ccc.android;
 
import java.util.ArrayList;
import java.util.List;
 
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PointF;
import android.os.Bundle;
import android.view.View;
 
public class DrawBoard extends Activity {
    public static final int openFile = 1, newFile = 2, saveFile = 3, help=4;
    List<PointF> points = new ArrayList<PointF>();
    Panel mPanel;
 
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mPanel = new Panel(this);
        setContentView(mPanel);
    }
 
    class Panel extends View {
        Paint mPaint = new Paint();
 
        public Panel(Context context) {
            super(context);
            mPaint.setColor(Color.YELLOW);
            mPaint.setStyle(Paint.Style.STROKE);
            mPaint.setStrokeWidth(3);
        }
 
        @Override
        public void onDraw(Canvas canvas) {
            for (int i=1; i<points.size();i++) {
                canvas.drawLine(points.get(i-1).x,points.get(i-1).y, 
                      points.get(i).x,points.get(i).y, mPaint);
            }
        }
 
        @Override
        public boolean onTouchEvent(android.view.MotionEvent event) {
            for (int i = 0; i < event.getHistorySize(); i++) {
                points.add(new PointF(event.getHistoricalX(i), event.getHistoricalY(i)));
            }
            Panel.this.invalidate();
            return true; // 代表該事件已被處理，不再向上傳遞了。
        };
    }
}

問題：無法處理兩筆劃以上的情形，因此我們修改上述程式，以處理兩筆劃以上的情形。

第二版

package ccc.android;
 
import java.util.ArrayList;
import java.util.List;
 
import android.app.Activity;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PointF;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
 
public class DrawBoard extends Activity {
    public static final int menuClear = 1;
    List<PointF> points = new ArrayList<PointF>();
    Panel mPanel;
 
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mPanel = new Panel(this);
        setContentView(mPanel);
    }
 
    public boolean onCreateOptionsMenu(Menu menu) {
        // menu.add 參數: (int groupId, int itemId, int order, int titleRes)
        menu.add(0, menuClear, 0, "清除");
        return true;
    }
 
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
          case menuClear: 
              points.clear();
              mPanel.invalidate();
              break;
        }
        return true;
    }
 
    class Panel extends View {
        Paint mPaint = new Paint();
 
        public Panel(Context context) {
            super(context);
            mPaint.setColor(Color.YELLOW);
            mPaint.setStyle(Paint.Style.STROKE);
            mPaint.setStrokeWidth(3);
        }
 
        @Override
        public void onDraw(Canvas canvas) {
            for (int i=1; i<points.size();i++) {
              PointF p1 = points.get(i-1);
              PointF p2 = points.get(i);
              if (Math.abs(p1.x - p2.x) < 20 
               && Math.abs(p1.y - p2.y) < 20) { 
                  canvas.drawLine(p1.x,p1.y, p2.x, p2.y, mPaint);
              }
            }
        }
 
        @Override
        public boolean onTouchEvent(android.view.MotionEvent event) {
            for (int i = 0; i < event.getHistorySize(); i++) {
                points.add(new PointF(event.getHistoricalX(i), event.getHistoricalY(i)));
            }
            Panel.this.invalidate();
            return true; // 代表該事件已被處理，不再向上傳遞了。
        };        
    }
}