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"?>
<Gallery xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/gallery"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
/>