加载大图片到内存

在android中要加载一张大图片到内存中如果通过如下方式进行

	 Bitmap bitmap= BitmapFactory.decodeFile("/sdcard/a.jpg");
		 iv.setImageBitmap(bitmap);

正确的做法应该是这样的：

public class MainActivity extends Activity {
	private ImageView iv;
	private int windowHeight;
	private int windowWidth;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		iv = (ImageView) findViewById(R.id.iv);
		WindowManager win = (WindowManager) getSystemService(WINDOW_SERVICE);
		windowHeight = win.getDefaultDisplay().getHeight();
		windowWidth = win.getDefaultDisplay().getWidth();
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

	public void load(View view) {
		
	/*	 Bitmap bitmap= BitmapFactory.decodeFile("/sdcard/a.jpg");
		 iv.setImageBitmap(bitmap);*/
		 
		// 图片解析的配置
		BitmapFactory.Options options = new Options();
		// 不去真的解析图片，只是获取图片的头部信息宽，高
		options.inJustDecodeBounds = true;
		BitmapFactory.decodeFile("/sdcard/a.jpg", options);
		int imageHeight = options.outHeight;
		int imageWidth = options.outWidth;
		// 计算缩放比例
		int scaleX = imageWidth / windowWidth;
		int scaleY = imageHeight / windowHeight;
		int scale = 1;
		if (scaleX > scaleY & scaleY >= 1) {
			scale = scaleX;

		}else if (scaleY > scaleX & scaleX >= 1) {
			scale = scaleY;

		}
		//真的解析图片
		options.inJustDecodeBounds=false;
		//设置采样率
		options.inSampleSize=scale;
		Bitmap bitmap=BitmapFactory.decodeFile("/sdcard/a.jpg", options);
		iv.setImageBitmap(bitmap);
	}

}