在android中顯示圖像也有好多種方法，本例中使用BitmapFactory.decodeResource獲得資源圖像檔案，然後用Canvas畫布顯示位圖。由于通過自定義View代替布局檔案，故而不需要使用布局檔案。
一、程式檔案
1、建立BitmapView.java檔案。
在“src/com.genwoxue.bitmap”位置，建立BitmapView.java檔案。
BitmapView.java檔案源代碼如下：
package com.genwoxue.bitmap;
import android.content.Context;
import android.content.res.Resources;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Color;
import android.view.View;
public class BitmapView extends View{
Paint paint=null;
Resources src=null;
Bitmap bmp=null;
public BitmapView(Context context) {
super(context);
/*----------------------------------------------
* 建議盡量把初始化畫筆、資源、位圖不放在onDraw方法中，這是因為：
* onDraw經常會運作 到的，不要在裡面new對象，越少越好，不然很浪費記憶體
*--------------------------------------------*/
//擷取畫筆paint，初始化畫筆
paint=new Paint();
//擷取資源src
src=getResources();
// 擷取位圖
bmp=BitmapFactory.decodeResource(src, R.drawable.ic_launcher);
}
@Override
protected void onDraw(Canvas canvas){
String info=null;
int posX=0;
int posY=0;
//設定畫布背景為灰色
canvas.drawColor(Color.GRAY);
//顯示位圖
canvas.drawBitmap(bmp,220,220,paint);
//設定畫筆為白色
paint.setColor(Color.WHITE);
//字型大小為18
paint.setTextSize(18);
info="圖檔高度："+bmp.getHeight()+",圖檔寬度："+bmp.getWidth();
posX=135;
posY=bmp.getWidth()+260;
//在posX與posY處顯示圖檔高度與寬度資訊
canvas.drawText(info, posX,posY, paint);
}
}
２、打開MainActivity.java主檔案
打開“src/com.genwoxue.bitmap/MainActivity.java”檔案。
MainActivity.java檔案源代碼如下：
package com.genwoxue.bitmap;
import android.os.Bundle;
import android.app.Activity;
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//執行個體化GraphicsView
BitmapView gv = new BitmapView(this);
/* 在以前我們通過setContentView(R.layout.activity_main)顯示布局檔案
* 本例中使用GraphicsView對象gv代替以前布局檔案
*/
setContentView(gv);
}
}
二、運作結果
附：android Bitmap用法總結
1、Drawable → Bitmap
public static Bitmap drawableToBitmap(Drawable drawable) {
Bitmap bitmap = Bitmap
.createBitmap(
drawable.getIntrinsicWidth(),
drawable.getIntrinsicHeight(),
drawable.getOpacity() != PixelFormat.OPAQUE ? Bitmap.Config.ARGB_8888
: Bitmap.Config.RGB_565);
Canvas canvas = new Canvas(bitmap);
// canvas.setBitmap(bitmap);
drawable.setBounds(0, 0, drawable.getIntrinsicWidth(),
drawable.getIntrinsicHeight());
drawable.draw(canvas);
return bitmap;
}
2、從資源中擷取Bitmap
Resources res=getResources();
Bitmap bmp=BitmapFactory.decodeResource(res, R.drawable.pic);
3、Bitmap → byte[]
private byte[] Bitmap2Bytes(Bitmap bm){
ByteArrayOutputStream baos = new ByteArrayOutputStream();
bm.compress(Bitmap.CompressFormat.PNG, 100, baos);
return baos.toByteArray();
}
4、byte[] → Bitmap
private Bitmap Bytes2Bimap(byte[] b){
if(b.length!=0){
return BitmapFactory.decodeByteArray(b, 0, b.length);
}
else {
return null;
}
}
5、儲存bitmap
static boolean saveBitmap2file(Bitmap bmp,String filename){
CompressFormat format= Bitmap.CompressFormat.JPEG;
int quality = 100;
OutputStream stream = null;
try {
stream = new FileOutputStream("/sdcard/" + filename);
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return bmp.compress(format, quality, stream);
}
6、将圖檔按自己的要求縮放
// 圖檔源
Bitmap bm = BitmapFactory.decodeStream(getResources()
.openRawResource(R.drawable.dog));
// 獲得圖檔的寬高
int width = bm.getWidth();
int height = bm.getHeight();
// 設定想要的大小
int newWidth = 320;
int newHeight = 480;
// 計算縮放比例
float scaleWidth = ((float) newWidth) / width;
float scaleHeight = ((float) newHeight) / height;
// 取得想要縮放的matrix參數
Matrix matrix = new Matrix();
matrix.postScale(scaleWidth, scaleHeight);
// 得到新的圖檔
Bitmap newbm = Bitmap.createBitmap(bm, 0, 0, width, height, matrix,
true);
// 放在畫布上
canvas.drawBitmap(newbm, 0, 0, paint);
7、bitmap的用法小結
BitmapFactory.Options option = new BitmapFactory.Options();
option.inSampleSize = 2; //将圖檔設為原來寬高的1/2，防止記憶體溢出
Bitmap bm = BitmapFactory.decodeFile("",option);//檔案流
URL url = new URL("");
InputStream is = url.openStream();
Bitmap bm = BitmapFactory.decodeStream(is);
android:scaleType：
android:scaleType是控制圖檔如何resized/moved來匹對ImageView的size。ImageView.ScaleType /
android:scaleType值的意義差別：
CENTER /center 按圖檔的原來size居中顯示，當圖檔長/寬超過View的長/寬，則截取圖檔的居中部分
顯示
CENTER_CROP / centerCrop 按比例擴大圖檔的size居中顯示，使得圖檔長(寬)等于或大于View的長
(寬)
CENTER_INSIDE / centerInside 将圖檔的内容完整居中顯示，通過按比例縮小或原來的size使得圖檔
長/寬等于或小于View的長/寬
FIT_CENTER / fitCenter 把圖檔按比例擴大/縮小到View的寬度，居中顯示
FIT_END / fitEnd 把圖檔按比例擴大/縮小到View的寬度，顯示在View的下部分位置
FIT_START / fitStart 把圖檔按比例擴大/縮小到View的寬度，顯示在View的上部分位置
FIT_XY / fitXY 把圖檔 不按比例 擴大/縮小到View的大小顯示
MATRIX / matrix 用矩陣來繪制，動态縮小放大圖檔來顯示。
//放大縮小圖檔
public static Bitmap zoomBitmap(Bitmap bitmap,int w,int h){
int width = bitmap.getWidth();
int height = bitmap.getHeight();
Matrix matrix = new Matrix();
float scaleWidht = ((float)w / width);
float scaleHeight = ((float)h / height);
matrix.postScale(scaleWidht, scaleHeight);
Bitmap newbmp = Bitmap.createBitmap(bitmap, 0, 0, width, height, matrix,
true);
return newbmp;
}
//将Drawable轉化為Bitmap
public static Bitmap drawableToBitmap(Drawable drawable){
int width = drawable.getIntrinsicWidth();
int height = drawable.getIntrinsicHeight();
Bitmap bitmap = Bitmap.createBitmap(width, height,
drawable.getOpacity() != PixelFormat.OPAQUE ? Bitmap.Config.ARGB_8888
: Bitmap.Config.RGB_565);
Canvas canvas = new Canvas(bitmap);
drawable.setBounds(0,0,width,height);
drawable.draw(canvas);
return bitmap;
}
//獲得圓角圖檔的方法
public static Bitmap getRoundedCornerBitmap(Bitmap bitmap,float roundPx){
Bitmap output = Bitmap.createBitmap(bitmap.getWidth(), bitmap
.getHeight(), Config.ARGB_8888);
Canvas canvas = new Canvas(output);
final int color = 0xff424242;
final Paint paint = new Paint();
final Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());
final RectF rectF = new RectF(rect);
paint.setAntiAlias(true);
canvas.drawARGB(0, 0, 0, 0);
paint.setColor(color);
canvas.drawRoundRect(rectF, roundPx, roundPx, paint);
paint.setXfermode(new PorterDuffXfermode(Mode.SRC_IN));
canvas.drawBitmap(bitmap, rect, rect, paint);
return output;
}
//獲得帶倒影的圖檔方法
public static Bitmap createReflectionImageWithOrigin(Bitmap bitmap){
final int reflectionGap = 4;
int width = bitmap.getWidth();
int height = bitmap.getHeight();
Matrix matrix = new Matrix();
matrix.preScale(1, -1);
Bitmap reflectionImage = Bitmap.createBitmap(bitmap,
0, height/2, width, height/2, matrix, false);
Bitmap bitmapWithReflection = Bitmap.createBitmap(width, (height + height/2),
Config.ARGB_8888);
Canvas canvas = new Canvas(bitmapWithReflection);
canvas.drawBitmap(bitmap, 0, 0, null);
Paint deafalutPaint = new Paint();
canvas.drawRect(0, height,width,height + reflectionGap,
deafalutPaint);
canvas.drawBitmap(reflectionImage, 0, height + reflectionGap, null);
Paint paint = new Paint();
LinearGradient shader = new LinearGradient(0,
bitmap.getHeight(), 0, bitmapWithReflection.getHeight()
+ reflectionGap, 0x70ffffff, 0x00ffffff, TileMode.CLAMP);
paint.setShader(shader);
// Set the Transfer mode to be porter duff and destination in
paint.setXfermode(new PorterDuffXfermode(Mode.DST_IN));
// Draw a rectangle using the paint with our linear gradient
canvas.drawRect(0, height, width, bitmapWithReflection.getHeight()
+ reflectionGap, paint);
return bitmapWithReflection;
}
}