Android系统中读写和显示图片

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"?>

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