Android Learning Multimedia Development---loading big picture

In practice, sometimes we need to load a large picture into memory from the SD card, but if your phone storage is very small, if you put this big picture directly into the content will cause the allocation failure and other abnormal problems. So we need a way to load the big picture into memory without the exception.

How can I load a large picture into memory without a memory overflow?

The Android system provides a way to load a picture by displaying a scale, which returns a smaller picture than the original.

1: First to get the picture parameters, the Android system provides a bitmapfactory this class

You can create a bitmap object that can obtain a picture resource from a different source.

Bitmapfactory.decoderesource (res, id)

Use the code above to get a bitmap object. The second parameter of the Bitmapfactory.decoderesource method can be used to get the parameters of a picture

Bitmapfactory.decoderesource (Getresources (), R.drawable.dog, opts);

2:options is a class that encapsulates the parameters of a picture

/*injustdecodebounds equals true: Represents the return of NULL, not bitmap object, but can get the source file parameter condition */    opts.injustdecodebounds = true;

3: Get the width and height of the screen

Gets the width and height of the display    DP = Getwindowmanager (). Getdefaultdisplay ();    int screenwidth = Dp.getwidth ();     int screenheight = Dp.getheight ();

4: Calculate the zoom ratio:

/* Calculate the magnification of the picture */    int scale = 1;    int scalewidth = imagewidth/screenwidth;    int scaleheight = imageheight/screenheight;        if (scalewidth >= scaleheight && scalewidth >= 1)    {scale    = ScaleWidth;    }    else if (ScaleHeight > ScaleWidth && scaleheight >= 1) {scale = ScaleHeight;}

5: Get the Bitmap object again, in a proportional way to get

/* Set the zoom ratio of the picture */    opts.insamplesize = scale;/* If greater than 1, request decoder to sample the original, return a smaller image*/    opts.injustdecodebounds = False ;    Bitmap Bitmap = Bitmapfactory.decoderesource (Getresources (), R.drawable.dog, opts);        /* Display picture */    ImageView IView = (ImageView) Findviewbyid (R.ID.IV);    Iview.setimagebitmap (bitmap);

The entire code:

public class Mainactivity extends Activity {        @Override     protected void OnCreate (Bundle savedinstancestate) {        super.oncreate ( savedinstancestate);        Setcontentview (R.layout.activity_main);                 Button button = (Button) Findviewbyid (R.id.button);        Button.setonclicklistener (new Onclicklistener () {                          @Override             public void OnClick (View arg0) {& nbsp;               //TODO auto-generated method stub                 log.i ("mainactivity", "onclick");                                 /* First parse this very big picture, get picture parameter situation */                options opts = new Options ();                 & nbsp              /*injustdecodebounds equals true: Represents the return of NULL, It is not a bitmap object, but it can get the parameter of the source file */                 Opts.injustdecodebounds = true;                                 //bitmapfactory This class is a bitmap object that is created by a different source                 bitmapfactory.decoderesource ( Getresources (), R.drawable.dog, opts);                                                 //Get image width and height                  int imagewidth = opts.outwidth;                int imageheight = opts.outheight;                                 //get screen width and height                  display dp = Getwindowmanager (). Getdefaultdisplay ();   & nbsp;            int screenwidth = Dp.getwidth ();                 int screenheight = Dp.getheight ();  & nbsp                                         /* Calculate the scale of the picture */                 int scale = 1;       & nbsp;        int scalewidth = imagewidth/screenwidth;       & nbsp;        int scaleheight = imageheight/screenheight;                                  if (scalewidth >= scaleheight && scalewidth >= 1)                  {                     scale = scalewidth;                }                 else if (ScaleHeight > ScaleWidth && scaleheight >= 1) {            & nbsp;       scale = scaleheight;                 }                                                  /* Set the scale of the picture */                 Opts.insamplesize = scale;/* If greater than 1, request decoder to sample the original, return a smaller image*/                opts.injustdecodebounds = false;                 bitmap Bitmap = Bitmapfactory.decoderesource (Getresources (), R.drawable.dog, opts);                     &nbsp          /* Show pictures */                 imageview IView = (ImageView) Findviewbyid (R.ID.IV);           & nbsp;    iview.setimagebitmap (bitmap);            }         });          }}

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Android Learning Multimedia Development---loading big picture