Android 图片加载相关问题

1、Android 图片加载过大导致内存溢出解决办法

public void loadImage(){
  //取得手机窗体的宽高
  WindowManager wm = this.getWind

owManager();
  int screenWidth = wm.getDefaultDisplay().getWidth();
  int screenHeight = wm.getDefaultDisplay().getHeight();

  //通过图片文件的信息，得到图片的宽高
  BitmapFactory.Options options = new Options();//解析位图附加条件
  options.inJustDecodeBounds = true;  //不去解析图像，只得到图像的文件信息
  Bitmap bitmap = BitmapFactory.decodeFile("File path",options);

  //得到图片宽高
  int imageWidth = options.outWidth;
  int imageHeight = options.outHeight;

  //计算缩放比
  int scaleWidth = imageWidth / screenWidth;
  int scaleHeight = imageHeight / screenHeight;

  //取得合适缩放比
  int scale = 1;
  if(scaleWidth > scaleHeight && scaleHeight > 1){
   scale = scaleWidth;
  }
  if(scaleHeight > scaleWidth && scaleWidth > 1){
   scale = scaleHeight;
  }

  //加载真是图片
  options.inSampleSize = scale;
  options.inJustDecodeBounds = false;
  bitmap = BitmapFactory.decodeFile("File Path", options);

  //将图片显示在你要显示的控件上
  //建议使用WeakReference代替强引用
 }

2.拷贝图片

public void copyImage(){
  //导入位图
  Bitmap bitmap = BitmapFactory.decodeResource(this.getResources(),R.drawable.ic_lock_idle_alarm);
  //创建一个图形的副本，此时的这个副本是空白的
  Bitmap alterBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(),     bitmap.getConfig());
  //准备一个画板，在上面放上准备好的空白的位图
  Canvas canvas = new Canvas();
  //准备一个画笔
  Paint paint = new Paint();
  paint.setColor(Color.WHITE);

  //画图
  Matrix m = new Matrix();
  canvas.drawBitmap(bitmap,m,paint);

 }

3、图形的缩放

//图形缩放函数（行列式）
Matrix matrix = new Matrix();
matrix.setValues(new float[] {
  1, 0, 0,
  0, 1, 0,
  0, 0, 1
});
x = 1x + 0y + 0z
y = 0x + 1y + 0z
z = 0x + 0y + 1z

通过canvas.drawBitmap(bmp, matrix, paint);
创建bitmap；
(1)水平缩放0.5
(2)垂直拉扯2倍

matrix.setScale(1.5f,1);//水平点放大到1.5f,垂直1

4、图形的旋转

Matrix matrix = new Matrix();
matrix.setRotate(15);
canvas.drawBitmap(bmp, matrix, paint);

5、消除锯齿

paint.setAntiAlias(true);  

6、指定圆心的旋转

matrix.setRotate(15,bmp.getWidth()/2,bmp.getHeight()/2);
Matrix matrix = new Matrix();
matrix.setRotate(15,bmp.getWidth()/2,bmp.getHeight()/2);
alteredBitmap = Bitmap.createBitmap(bmp, 0, 0, bmp.getWidth(), bmp.getHeight(),
matrix, false);
alteredImageView.setImageBitmap(alteredBitmap);