Android系統中讀寫和顯示圖片

1.    在畫布上繪製(Draw with a Canvas) 

Android提供了自訂的繪製API，可以繪製各種圖形，文字，映像對象在Canvas上，而事

實上所有在Canvas對想都會被繪製到Canvas底層的Bitmap對象上面，建立一個Canvas

對象的語句如下：

Bitmap b =Bitmap.createBitmap(100, 100, Bitmap.Config.ARGB_8888);

Canvas c =new Canvas(b);

首先建立一個32位的位元影像對象，類型是ARGB，然後在這個位元影像對象上建立一個畫布（Canvas）

對象。

 

view.draw(c);

FileOutputStreamfos = new FileOutputStream (new File (APP_FILE_PATH +"/Canvastoimage.png"));

bitmap.compress(Bitmap.CompressFormat.JPEG,100, fos);

將View中內容輸出到映像，壓縮映像到指定格式JPG.其中fos為檔案輸出資料流。

 

在Android對象上顯示Canvas的內容，要重載View的onDraw()方法，這點跟Java Swing

中要重寫JComponent的paintComponent()方法有點類似，這樣可以擷取圖形系統的繪製對

象，從而實現自訂對象的繪製。一個完整的重寫View實現Canvas繪製顯示的代碼如下：

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);        }    }}

程式效果如下：

2.    使用可繪製對象(Drawables Object)

Android中還提供一種相對簡單和便捷的API用來讀寫和顯示影像檔，就是以resource的形式載入圖片對象，

使用ImageView API來對映像顯示，如果有多個映像資源還可以使用Gallery來實現顯示。大致的順序為：

1.    將要顯示的圖片放到資源檔夾中

2.    定義資源ID對象數組

3.    在layout.xml中定義Gallery

4.    實現一個BaseAdapter

5.    在Activity中載入和指派對應的Adapter.

程式效果如下：

程式是我從android內建的Demo中修改來的，人懶啊！程式原始碼如下：

Activity的代碼：

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介面代碼：

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"/>