import android.os.Bundle;
import android.os.Environment;
import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.BitmapFactory.Options;
import android.view.Menu;
import android.view.View;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.ImageView;

public class MainActivity extends Activity {
    private Button btn_loadimage;
    private ImageView iv_bigimage;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        btn_loadimage = (Button) findViewById(R.id.btn_loadimage);
        iv_bigimage = (ImageView) findViewById(R.id.iv_bigimage);

        btn_loadimage.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // Bitmap bitmap=BitmapFactory.decodeFile("/sdcard/a.jpg");
                // iv_bigimage.setImageBitmap(bitmap);

                BitmapFactory.Options opts = new Options();
                // 不讀取像素?cái)?shù)組到內(nèi)存中，僅讀取圖片的信息
                opts.inJustDecodeBounds = true;
                BitmapFactory.decodeFile("/sdcard/a.jpg", opts);
                // 從Options中獲取圖片的分辨率
                int imageHeight = opts.outHeight;
                int imageWidth = opts.outWidth;

                // 獲取Android屏幕的服務(wù)
                WindowManager wm = (WindowManager) getSystemService(WINDOW_SERVICE);
                // 獲取屏幕的分辨率，getHeight()、getWidth已經(jīng)被廢棄掉了
                // 應(yīng)該使用getSize()，但是這里為了向下兼容所以依然使用它們
                int windowHeight = wm.getDefaultDisplay().getHeight();
                int windowWidth = wm.getDefaultDisplay().getWidth();

                // 計(jì)算采樣率
                int scaleX = imageWidth / windowWidth;
                int scaleY = imageHeight / windowHeight;
                int scale = 1;
                // 采樣率依照最大的方向?yàn)闇?zhǔn)
                if (scaleX > scaleY && scaleY >= 1) {
                    scale = scaleX;
                }
                if (scaleX < scaleY && scaleX >= 1) {
                    scale = scaleY;
                }

                // false表示讀取圖片像素?cái)?shù)組到內(nèi)存中，依照設(shè)定的采樣率
                opts.inJustDecodeBounds = false;
                // 采樣率
                opts.inSampleSize = scale;
                Bitmap bitmap = BitmapFactory.decodeFile("/sdcard/a.jpg", opts);
                iv_bigimage.setImageBitmap(bitmap);

            }
        });
    }
}