Develop Reference

How can I correctly use the Canvas class to show an image into an ImageView in this simple Android app?

I am absolulty new in Android and I am doing some experiment with the Canvas object.
I am trying to add it to a Canvas and then show it into a retrieved ImageView (I know that this is not the standard and simplest way to show an image into an ImageView but this is only a simplified experiment for a further more complex thing that I have to do using Canvas).
So I have a star.png (a 32x32 px icon into my /res/drawable/ folder) and I am trying to
This is my activity_main.xml layout configuration file:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!" />
<ImageView
android:id="#+id/star_container"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
</LinearLayout>
This layout contain the ImageView having id=star_container that is where I have to draw the image using the Canvas
And this is the MainActivity class that handle this view:
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ImageView imgView = (ImageView) findViewById(R.id.star_container);
Canvas canvas;
Bitmap star = BitmapFactory.decodeResource(getResources(), R.drawable.star);
Bitmap output = Bitmap.createBitmap(32, 32, Bitmap.Config.ARGB_8888);
canvas = new Canvas(output);
canvas.drawBitmap(star, star.getWidth() + 2, 0, null);
imgView.setImageDrawable(new BitmapDrawable(getResources(), output));
}
}
So into the onCreate() method I retrieve the ImageView where the image have to be placed. Then I create a Bitmap object retrieving the star.png image from the resoruces that will be added to the otuput Bitmap using the Canvas.
Finally I set this output Bitmap into the retrieve ImageView.
So I expected that, when the app is running, the previous ImageView contains the star.png image but it does not appear.
I have no error when I execute this app but the only output that I obtain is the textual message defined into the TextView.
Why? What is wrong? What am I missing? How can I modify this code and let it work?

According to the documents:
left: The position of the left side of the bitmap being drawn
The problem is here :
canvas.drawBitmap(star, star.getWidth() + 2, 0, null);
You're using a value for left that is out of bitmap bounds, So nothing is drawn, try this: canvas.drawBitmap(star, 0, 0, null);
Android API provides another method to set Bitmap as drawable directly :
ImageView#setImageBitmap(Bitmap bm)
I think it's a better practice to implement a custom View and explore Canvas capabilities there (in onDraw method)

another way - using rect area:
Canvas canvas;
Bitmap star = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);
Bitmap output = Bitmap.createBitmap(star.getWidth(), star.getHeight(), Bitmap.Config.ARGB_8888);
canvas = new Canvas(output);
Rect source = new Rect(0, 0, star.getWidth(), star.getHeight());
canvas.drawBitmap(star, null, source, null);
imgView.setImageBitmap(output);

how to load image with Universal ImageLoader without displaying

I'm trying to do something like this:
Android Map api v2 Custom marker with ImageView
But I'm stuck on using image loader.
Trying:
Bitmap bmImg = imageLoader.loadImageSync(url);
LogCat gives me
04-13 14:11:44.953: E/ImageLoader(18542): android.os.NetworkOnMainThreadException
Here's is my code. I have an ArrayList camera with all information needed (titrle, position, url, etc).
public void drawPicsOnMap()
{
String title = null;
String place = null;
for (int i = 0; i<camera.size(); i++)
{
Bitmap.Config conf = Bitmap.Config.ARGB_8888;
Bitmap bmp = Bitmap.createBitmap(80, 80, conf);
Canvas canvas = new Canvas(bmp);
// paint defines the text color,
// stroke width, size
Paint color = new Paint();
color.setTextSize(35);
color.setColor(Color.BLACK);
Camera cam = camera.get(i);
LatLng coord = new LatLng(cam.lat, cam.lon);
title = Integer.toString(cam.id);
place = cam.place;
String url = cam.img;
Bitmap bmImg = imageLoader.loadImageSync(url);
//modify canvas
canvas.drawBitmap(bmImg, 0,0, color);
canvas.drawText(title, 30, 40, color);
Marker mark = map.addMarker(new MarkerOptions()
.position(coord)
.title(title)
.snippet(place)
.icon(BitmapDescriptorFactory
.fromBitmap(bmp)));
markers.put(mark.getId(), url);
}
}

Try this:
imageLoader.loadImage(url, new SimpleImageLoadingListener(){
#Override
public void onLoadingComplete(String imageUri, View view,
Bitmap loadedImage) {
super.onLoadingComplete(imageUri, view, loadedImage);
//write your code here to use loadedImage
}
});
Here
onLoadingComplete will be called on UI thread which makes it thread safe

You can not do any networking on the main thread. See for description. UIL usually creates the thread and stuff for you when you call displayImage, but loadImageSync does not. Either create a thread and load it or use an AsynTask.

Is it possible to create a bitmap, add it to canvas and draw it using view.draw?

For example ..
Bitmap myPic = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);
Bitmap newPic = Bitmap.createScaledBitmap(myPic, 50, 50, true);
Canvas myCanv = new Canvas(newPic);
View myView = (View)findViewById(R.id.view1);
myView.draw(myCanv);
is something like the above feasible?

You really shouldn't do it like that. My recommendation is to do it like this
Bitmap myPic = BitmapFactory.decodeResource(getResources(), R.drawable.ic_launcher);
myPic = Bitmap.createScaledBitmap(myPic,50,50, true);
BitmapDrawable draw = new BitmapDrawable(this.getResources(), myPic);
View myView = (View) findViewById (R.id.view1);
myView.setBackground(draw);
This way you pass your View a drawable as a background.
If you really want to set a Bitmap as your source then you should make an ImageView

Fetch Current image from horizontol scroll bar android

I am trying to make a simple image gallery through which I can set wallpaper; I am using the below code to fetch the files from download folder and display it in scroll view.
I am able to do that, but now I want to fetch the currently displayed image so that I can set that image as wallpaper.
Below is the code I have for my activity class:
public class MainActivity extends Activity {
LinearLayout myGallery;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
myGallery = (LinearLayout)findViewById(R.id.mygallery);
String ExternalStorageDirectoryPath = Environment
.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS)
.getAbsolutePath();
String targetPath = ExternalStorageDirectoryPath ;
Toast.makeText(getApplicationContext(), targetPath, Toast.LENGTH_LONG).show();
File targetDirector = new File(targetPath);
File[] files = targetDirector.listFiles();
for (File file : files){
myGallery.addView(insertPhoto(file.getAbsolutePath()));
}
}
View insertPhoto(String path){
Bitmap bm = decodeSampledBitmapFromUri(path, 520, 520);
LinearLayout layout = new LinearLayout(getApplicationContext());
layout.setLayoutParams(new LayoutParams(550, 550));//Size of view
layout.setGravity(Gravity.CENTER);
ImageView imageView = new ImageView(getApplicationContext());
imageView.setLayoutParams(new LayoutParams(520, 520));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setImageBitmap(bm);
layout.addView(imageView);
return layout;
}
public Bitmap decodeSampledBitmapFromUri(String path, int reqWidth, int reqHeight) {
Bitmap bm = null;
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeFile(path, options);
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);
// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
bm = BitmapFactory.decodeFile(path, options);
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;
}
}
Please tell me how I can fetch the image which is currently displayed in the scroll view.
Thanks
Aman

its been 5 months yet not answered, but i think i will try to answer it.
I think you need a custom view ie. with canvas. create a canvas and then create a bitmap in canvas. After that when you get a bitmap from linear layout in the form of URI, in your code a method decodeSampledBitmapFromUri you are getting a bitmap, simply assign the bitmap to the created bitmap on the canvas.

Use Current Wallpaper as live wallpaper background

I am getting the current wallpaper by using following code:
final WallpaperManager wallpaperManager = WallpaperManager.getInstance(this);
final Drawable wallpaperDrawable = wallpaperManager.getDrawable();
How can I create a bitmap from this?
like when I create a bitmap from res folder I use this
Resources res = getApplicationContext().getResources();
b = BitmapFactory.decodeResource(res, R.drawable.wall);
What code I should use to get current wallpaper into the bitmap so I can draw it on my canvas and use it as my live wallpaper background?

The Drawable fetched should really be a BitmapDrawable. You can verify this using instanceof if necessary.
That being the case, all you have to do is:
final Drawable wallpaperDrawable = wallpaperManager.getDrawable();
final Bitmap wallpaperBitmap = ((BitmapDrawable) wallpaperDrawable).getBitmap();
EDIT: If it turns out that the Drawable is NOT a BitmapDrawable, you can use the following method to convert it (found in this answer, credit to André):
public static Bitmap drawableToBitmap(Drawable drawable) {
if (drawable instanceof BitmapDrawable) {
return ((BitmapDrawable)drawable).getBitmap();
}
Bitmap bitmap = Bitmap.createBitmap(drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight(), Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
drawable.setBounds(0, 0, canvas.getWidth(), canvas.getHeight());
drawable.draw(canvas);
return bitmap;
}