1. 在画布上绘制(Draw with a Canvas)
Android提供了自定义的绘制API，可以绘制各种图形，文字，图像对象在Canvas上，而事
实上所有在Canvas对想都会被绘制到Canvas底层的Bitmap对象上面，创建一个Canvas
对象的语句如下：
Bitmap b =Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);
Canvas c =new Canvas(b);
首先创建一个32位的位图对象，类型是ARGB，然后在这个位图对象上创建一个画布（Canvas）
对象。
view.draw(c);
FileOutputStreamfos = new FileOutputStream (new File (APP_FILE_PATH +"/Canvastoimage.png"));
bitmap.compress(Bitmap.CompressFormat.JPEG,100, fos);
将View中内容输出到图像，压缩图像到指定格式JPG.其中fos为文件输出流。
在Android对象上显示Canvas的内容，要重载View的onDraw()方法，这点跟Java Swing
中要重写JComponent的paintComponent()方法有点类似，这样可以获取图形系统的绘制对
象，从而实现自定义对象的绘制。一个完整的重写View实现Canvas绘制显示的代码如下：
package com.gloomyfish; import android.app.Activity; import android.content.Context; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import android.graphics.Paint.Style; import android.os.Bundle; import android.view.View; import android.view.Window; public class GraphicHelloActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); requestWindowFeature(Window.FEATURE_NO_TITLE); setContentView(new Panel(this)); } class Panel extends View { public Panel(Context context) { super(context); } @Override public void onDraw(Canvas canvas) { Bitmap _scratch = BitmapFactory.decodeResource(getResources(), R.drawable.flower_001); canvas.drawColor(Color.WHITE); canvas.drawBitmap(_scratch, 0, 0, null); Paint paint = new Paint(); paint.setColor(Color.GREEN); paint.setStyle(Style.FILL); paint.setTextSize(16); canvas.drawText("Hello, Android Canvas", 20, 80, paint); } } }
程序效果如下：
2. 使用可绘制对象(Drawables Object)
Android中还提供一种相对简单和便捷的API用来读写和显示图像文件，就是以resource的形式加载图片对象，
使用ImageView API来对图像显示，如果有多个图像资源还可以使用Gallery来实现显示。大致的顺序为：
1. 将要显示的图片放到资源文件夹中
2. 定义资源ID对象数组
3. 在layout.xml中定义Gallery
4. 实现一个BaseAdapter
5. 在Activity中加载和指派对应的Adapter.
程序效果如下：
程序是我从android自带的Demo中修改来的，人懒啊！程序源代码如下：
Activity的代码：
package com.gloomyfish.gallery; import android.app.Activity; import android.os.Bundle; import android.view.View; import android.widget.AdapterView; import android.widget.Gallery; import android.widget.Toast; import android.widget.AdapterView.OnItemClickListener; public class HellGalleryActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); Gallery gallery = (Gallery) findViewById(R.id.gallery); gallery.setAdapter(new ImageAdapter(this)); gallery.setOnItemClickListener(new OnItemClickListener() { public void onItemClick(AdapterView parent, View v, int position, long id) { Toast.makeText(HellGalleryActivity.this, "" + position, Toast.LENGTH_SHORT).show(); } }); } }
ImageAdapter /ImageView接口代码：
package com.gloomyfish.gallery; import android.content.Context; import android.content.res.TypedArray; import android.view.View; import android.view.ViewGroup; import android.widget.BaseAdapter; import android.widget.Gallery; import android.widget.ImageView; public class ImageAdapter extends BaseAdapter { int mGalleryItemBackground; private Context mContext; private Integer[] mImageIds = { R.drawable.sample_0, R.drawable.sample_1, R.drawable.sample_2, R.drawable.sample_3, R.drawable.sample_4, R.drawable.sample_5, R.drawable.sample_6, R.drawable.sample_7 }; public ImageAdapter(Context c) { mContext = c; TypedArray attr = mContext.obtainStyledAttributes(R.styleable.HelloGallery); mGalleryItemBackground = attr.getResourceId( R.styleable.HelloGallery_android_galleryItemBackground, 0); attr.recycle(); } public int getCount() { return mImageIds.length; } public Object getItem(int position) { return position; } public long getItemId(int position) { return position; } public View getView(int position, View convertView, ViewGroup parent) { ImageView imageView = new ImageView(mContext); imageView.setImageResource(mImageIds[position]); imageView.setLayoutParams(new Gallery.LayoutParams(200, 200)); imageView.setScaleType(ImageView.ScaleType.FIT_XY); imageView.setBackgroundResource(mGalleryItemBackground); return imageView; } }
layout/main.xml的配置如下：
<?xml version="1.0" encoding="utf-8"?> <Gallery xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/gallery" android:layout_width="fill_parent" android:layout_height="wrap_content" />
