前言

通过自定义的一个画布view，在上面进行画笔的事件监听。

Android代码：

要实现画图我们需要画布、画笔，所以我们自定义一个继承于view的类。
画笔需要完成的工作是，当有监听到动作时，把路径设置一下，移动的话就在两点之间所有坐标标记，点击的话在那点的坐标标记。这些东西要有一个路径path存起来，然后画布canvas根据这些path在画布上显示。

package cn.zhuangzhihuang.mydrawview;

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

public class DrawView extends View{

	private Paint paint;
	private Path path;

	public DrawView(Context context, AttributeSet attrs) {
		super(context, attrs);
		
		//------------设置画笔--------------
		paint = new Paint();
		paint.setColor(Color.GRAY);
		paint.setStrokeWidth(2);
		paint.setStyle(Style.STROKE);
		
		path = new Path();		
		
	}
	
	@Override
	protected void onDraw(Canvas canvas) {
		// TODO Auto-generated method stub
		super.onDraw(canvas);
		canvas.drawPath(path,paint);
	// Log.i("DrawView","draw");
	}
	
	@Override
	public boolean onTouchEvent(MotionEvent event) {
		// TODO Auto-generated method stub
		int key = event.getAction();
		float x = event.getX();
		float y = event.getY();
		switch (key) {
		case MotionEvent.ACTION_DOWN:
			path.moveTo(x, y);
			break;
		case MotionEvent.ACTION_MOVE:
			path.lineTo(x, y);
			break;
		case MotionEvent.ACTION_UP:
			
			break;
		default:
			break;
		}		
		invalidate();  //刷新
		return true;
	}
	
	public void clear() {
		path.reset();
		invalidate();
	}

}

MainActivity:

package cn.zhuangzhihuang.mydrawview;

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


public class MainActivity extends Activity {

    private DrawView tv_draw;

	@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        tv_draw = (DrawView)findViewById(R.id.tv_draw);
    }


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

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_clear) {
        	tv_draw.clear();
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}


<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" >

    <cn.zhuangzhihuang.mydrawview.DrawView android:id="@+id/tv_draw" android:layout_width="wrap_content" android:layout_height="wrap_content" />

</FrameLayout>