Thứ Bảy, 14 tháng 7, 2012

Scale bitmap Efficiently

0
04:21
Remark: I have a exercise "Display Gallery selected image using BitmapFactory" before. The original idea is to select image using Android build-in app Gallery, and display on a ImageView, FOR SMALL IMAGE. Recently found that it cannot display large image, such as original photos from camera ~ but I don't know why no error reported!!!

It may be due to the Bitmap is too large for the ImageView. To scale-down the bitmap before display, Android Developer Site have a good article to describe "Loading Large Bitmaps Efficiently".


The old exercise is modified with scale-down bitmap and re-posted here:

with scale-down bitmap


Main Code:
package com.example.androidselectimage;

import java.io.FileNotFoundException;

import android.net.Uri;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {

TextView textTargetUri;
ImageView targetImage;

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

Button buttonLoadImage = (Button)findViewById(R.id.loadimage);
textTargetUri = (TextView)findViewById(R.id.targeturi);
targetImage = (ImageView)findViewById(R.id.targetimage);

buttonLoadImage.setOnClickListener(new Button.OnClickListener(){

@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
Intent intent = new Intent(Intent.ACTION_PICK,
android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
startActivityForResult(intent, 0);
}});

}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
// TODO Auto-generated method stub
super.onActivityResult(requestCode, resultCode, data);

if (resultCode == RESULT_OK){
Uri targetUri = data.getData();
textTargetUri.setText(targetUri.toString());

Toast.makeText(getApplicationContext(),
"ImageView: " + targetImage.getWidth() + " x " + targetImage.getHeight(),
Toast.LENGTH_LONG).show();

Bitmap bitmap;
bitmap = decodeSampledBitmapFromUri(
targetUri,
targetImage.getWidth(), targetImage.getHeight());

if(bitmap == null){
Toast.makeText(getApplicationContext(), "the image data could not be decoded", Toast.LENGTH_LONG).show();

}else{
Toast.makeText(getApplicationContext(),
"Decoded Bitmap: " + bitmap.getWidth() + " x " + bitmap.getHeight(),
Toast.LENGTH_LONG).show();
targetImage.setImageBitmap(bitmap);
}
}
}

/*
* How to "Loading Large Bitmaps Efficiently"?
* Refer: http://developer.android.com/training/displaying-bitmaps/load-bitmap.html
*/

public Bitmap decodeSampledBitmapFromUri(Uri uri, int reqWidth, int reqHeight) {

Bitmap bm = null;

try{
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeStream(getContentResolver().openInputStream(uri), null, options);

// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
bm = BitmapFactory.decodeStream(getContentResolver().openInputStream(uri), null, options);
} catch (FileNotFoundException e) {
e.printStackTrace();
Toast.makeText(getApplicationContext(), e.toString(), Toast.LENGTH_LONG).show();
}

return bm;
}

public int calculateInSampleSize(
BitmapFactory.Options options, int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 1;

if (height > reqHeight || width > reqWidth) {
if (width > height) {
inSampleSize = Math.round((float)height / (float)reqHeight);
} else {
inSampleSize = Math.round((float)width / (float)reqWidth);
}
}
return inSampleSize;
}

}


Layout:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="@string/hello_world" />
<Button
android:id="@+id/loadimage"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Load Image" />
<TextView
android:id="@+id/targeturi"
android:layout_width="fill_parent"
android:layout_height="wrap_content" />
<ImageView
android:id="@+id/targetimage"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:scaleType="centerCrop" />
</LinearLayout>


Download the files.

About the author

Donec non enim in turpis pulvinar facilisis. Ut felis. Praesent dapibus, neque id cursus faucibus. Aenean fermentum, eget tincidunt.

0 nhận xét:

Lưu ý: Chỉ thành viên của blog này mới được đăng nhận xét.