写字板

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <com.example.guaguaka.GuaGuaKa
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" />

</RelativeLayout>

MainActivity

package com.example.guaguaka;

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

public class MainActivity extends Activity {

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
	}

}

GuaGuaKa

package com.example.guaguaka;

import android.R.integer;
import android.annotation.SuppressLint;
import android.app.usage.UsageEvents.Event;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.Paint.Style;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class GuaGuaKa extends View {

	/**
	 * 画笔,画布，路径，图片，坐标值
	 */
	private Paint mOutterPaint = new Paint();
	private Path mPath = new Path();

	private int mLastX;
	private int mLastY;

	/** 构造器 */
	public GuaGuaKa(Context context, AttributeSet attrs, int defStyleAttr) {
		super(context, attrs, defStyleAttr);
	}

	public GuaGuaKa(Context context) {
		this(context, null);
	}

	public GuaGuaKa(Context context, AttributeSet attrs) {
		this(context, attrs, 0);
	}


	@SuppressLint("DrawAllocation")
	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		super.onMeasure(widthMeasureSpec, heightMeasureSpec);
		int width = getMeasuredWidth();
		int height = getMeasuredHeight();
		// 画笔的属性
		initPaint();
	}

	private void initPaint() {
		mOutterPaint.setColor(Color.RED);
		mOutterPaint.setAntiAlias(true);
		mOutterPaint.setDither(true);
		mOutterPaint.setStyle(Paint.Style.STROKE);
		mOutterPaint.setStrokeJoin(Paint.Join.ROUND); // 圆角
		mOutterPaint.setStrokeCap(Paint.Cap.ROUND); // 圆角
		// 设置画笔宽度
		mOutterPaint.setStrokeWidth(20);

	}

	@Override
	protected void onDraw(Canvas canvas) {
		// TODO Auto-generated method stub
		canvas.drawPath(mPath, mOutterPaint);
	}

	@Override
	public boolean onTouchEvent(MotionEvent event) {
		// TODO Auto-generated method stub
		int action = event.getAction();
		int x = (int) event.getX();
		int y = (int) event.getY();
		switch (action) {
		case MotionEvent.ACTION_DOWN:
			mLastX = x;
			mLastY = y;
			mPath.moveTo(mLastX, mLastY);
			break;
		case MotionEvent.ACTION_MOVE:

			mPath.lineTo(x, y);
			mLastX = x;
			mLastY = y;
			break;
		case MotionEvent.ACTION_UP:

			break;

		default:
			break;
		}
		invalidate();
		return true;
	}

}