017_04Canvas和Paint的用法

　　Canvas类就是表示一块画布，你可以在上面画你想画的东西。当然，你还可以设置画布的属性，如画布的颜色/尺寸等。

　　Paint     画笔 和Canvas搭配使用,用于指定绘制的颜色, 线条的粗细, 过渡, 渐变等效果.

package com.example.day17_04simplepainter;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.Bitmap.CompressFormat;
import android.graphics.Bitmap.Config;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.ImageView;

public class MainActivity extends Activity implements OnTouchListener {

    private ImageView iv_painter;
    private Bitmap bitmap;
    private Canvas canvas;
    private Paint paint;
    int startX =0;
    int startY=0;
    int stopX=0;
    int stopY =0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        iv_painter = (ImageView) findViewById(R.id.iv_painter);    
        iv_painter.setOnTouchListener(this);
     }

    @Override
    public boolean onTouch(View v, MotionEvent event) {
        
        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            
            if (bitmap==null) {
                bitmap = Bitmap.createBitmap(iv_painter.getWidth(), iv_painter.getHeight(), Config.ARGB_8888);
                canvas = new Canvas(bitmap);
                canvas.drawColor(Color.WHITE);
                paint = new Paint();
                paint.setStrokeWidth(10);
                paint.setColor(Color.GREEN);
            }
            startX = (int) event.getX();
            startY = (int) event.getY();    
            System.out.println("MainActivity.onTouch()ACTION_DOWN");
            break;
            
        case MotionEvent.ACTION_MOVE:
            System.out.println("MainActivity.onTouch()ACTION_MOVE");
            
            stopX = (int) event.getX();
            stopY = (int) event.getY();
            canvas.drawLine(startX, startY, stopX, stopY, paint);
            iv_painter.setImageBitmap(bitmap);
        
            startX=stopX;
            startY=stopY;
               
            break;    
            
        case MotionEvent.ACTION_UP:    
            break;
        default:
            break;
        }
        return true;
    }
    
    public void save(View v){
        FileOutputStream fos;
        try {
            fos = new FileOutputStream(getFilesDir()+"/mypaint.jpg");
            bitmap.compress(CompressFormat.JPEG, 100, fos);
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }        
    } 
}

<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"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.day17_04simplepainter.MainActivity" >

    <ImageView 
        android:id="@+id/iv_painter"
        android:layout_width="300px"
        android:layout_height="400px" />
    
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="save" 
        android:onClick="save"
        android:layout_alignParentBottom="true"/>
</RelativeLayout>