android开发笔记之多媒体—大图片的加载

1.将图片导入到SD卡



2.从SD中获取图片

String path = Environment.getExternalStorageDirectory() + "/img_big_1.jpg";
bitmap = BitmapFactory.decodeFile(path, options);

3.为这种图片设置采样率（即压缩比）

Options options = new Options();
//设置图片的采样率
options.inSampleSize = scale;  //假设为4，表示原来宽高的1/4,原来为2560*1600变成了640*400

4.最后将图片显示到ImageView组件上

iv.setImageBitmap(bitmap);

5.加上相应权限

//读SD卡的权限
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.MEDIA_CONTENT_CONTROL"/>

不过我们这次这个采样率得计算一下，因为我们需要让图片以最合适的大小显示到当前屏幕上：

private Bitmap getScaleBitmap(String path) {
Bitmap bitmap = null;
try {
ExifInterface exifInterface = new ExifInterface(path);
imageWidth = exifInterface.getAttributeInt(ExifInterface.TAG_IMAGE_WIDTH, 0);
imageHeight = exifInterface.getAttributeInt(ExifInterface.TAG_IMAGE_LENGTH, 0);
int scaleX = (int) (imageWidth*0.1f/screenWidth + 0.5f); //加0.5f是为了四舍五入
int scaleY = (int) (imageHeight*0.1f/screenHeight + 0.5f);
int scale = (int)( Math.sqrt(scaleX*scaleX + scaleY*scaleY) + 0.5f);
Options options = new Options();
//设置图片的采样率
options.inSampleSize = scale;  //假设为4，表示原来宽高的1/4,原来为2560*1600变成了640*400
bitmap = BitmapFactory.decodeFile(path, options);
} catch (IOException e) {
e.printStackTrace();
}
return bitmap;
}

当然要知道这个比，就还应该得到屏幕的宽高

// 获取Android屏幕的信息
private void getScreenWith() {
//三种方式
//第一种
//      WindowManager windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
//      width = windowManager.getDefaultDisplay().getWidth();
//      height = windowManager.getDefaultDisplay().getHeight();

//第二种
//      Point point = new Point();
//      WindowManager windowManager = (WindowManager)       getSystemService(WINDOW_SERVICE);
//      windowManager.getDefaultDisplay().getSize(point);
//      width = point.x;
//      height = point.y;

//第三种
DisplayMetrics metric = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(metric);
screenWidth = metric.widthPixels;   //屏幕宽度
screenHeight = metric.heightPixels;  //屏幕高度
}

核心代码：

/**
* 从SD卡中加载大图片
* @author Administrator
*
*/
public class MainActivity extends Activity {

private ImageView iv;
private int screenWidth,screenHeight; //屏幕的宽高
private int imageWidth,imageHeight;   //图片的宽高
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
iv = (ImageView) findViewById(R.id.iv);
}
//从SD卡中加载图片
public void loadimage(View view) {
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
String path = Environment.getExternalStorageDirectory() + "/img_big_1.jpg";
getScreenWith();
Bitmap bitmap = getScaleBitmap(path);
iv.setImageBitmap(bitmap);
}else {
Toast.makeText(this, "SD卡不存在或不可用", Toast.LENGTH_LONG).show();
}
}
private Bitmap getScaleBitmap(String path) {
Bitmap bitmap = null;
try {
ExifInterface exifInterface = new ExifInterface(path);
imageWidth = exifInterface.getAttributeInt(ExifInterface.TAG_IMAGE_WIDTH, 0);
imageHeight = exifInterface.getAttributeInt(ExifInterface.TAG_IMAGE_LENGTH, 0);
int scaleX = (int) (imageWidth*0.1f/screenWidth + 0.5f); //加0.5f是为了四舍五入
int scaleY = (int) (imageHeight*0.1f/screenHeight + 0.5f);
int scale = (int)( Math.sqrt(scaleX*scaleX + scaleY*scaleY) + 0.5f);
Options options = new Options();
//设置图片的采样率
options.inSampleSize = scale;  //假设为4，表示原来宽高的1/4,原来为2560*1600变成了640*400
bitmap = BitmapFactory.decodeFile(path, options);
} catch (IOException e) {
e.printStackTrace();
}
return bitmap;
}
// 获取Android屏幕的信息
private void getScreenWith() {
//三种方式
//第一种
//      WindowManager windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
//      width = windowManager.getDefaultDisplay().getWidth();
//      height = windowManager.getDefaultDisplay().getHeight();
//第二种
//      Point point = new Point();
//      WindowManager windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
//      windowManager.getDefaultDisplay().getSize(point);
//      width = point.x;
//      height = point.y;
//第三种
DisplayMetrics metric = new DisplayMetrics();
getWindowManager().getDefaultDisplay().getMetrics(metric);
screenWidth = metric.widthPixels;   //屏幕宽度
screenHeight = metric.heightPixels;  //屏幕高度
}
}

结果：