Getting the dimensions of an ImageView in Android development can be surprisingly tricky. Many new developers assume direct access to height and width properties will work immediately after declaring the ImageView. However, this often leads to incorrect values, usually returning zero. Understanding the Android layout lifecycle is key to retrieving accurate dimensions. This post dives into several reliable methods for obtaining the correct width and height of an ImageView, explaining the underlying reasons and providing practical examples for various scenarios. We’ll cover techniques for different stages of the layout process, ensuring you can get the dimensions you need when you need them.

Understanding the Android Layout Lifecycle

Before diving into the solutions, it’s crucial to understand how Android draws views. The layout process occurs in phases: measurement, layout, and draw. Attempting to access dimensions before the layout phase completes will yield inaccurate results. This is why simply calling getWidth() or getHeight() immediately after declaring the ImageView usually returns zero. The view hasn’t been measured and placed on the screen yet.

Think of it like baking a cake. You can’t measure the cake’s height before it’s finished baking and cooling. Similarly, you need to wait for the Android layout process to complete before accurately determining the ImageView dimensions.

This asynchronous nature requires us to employ specific techniques that ensure we access the dimensions at the right moment.

Using onPreDrawListener

One reliable method is using ViewTreeObserver.OnPreDrawListener. This listener gets triggered just before the view is drawn on the screen, guaranteeing that the layout process is complete and the dimensions are accurate. This approach is versatile and works well in most scenarios.

Here’s how to implement it:

1. Attach an OnPreDrawListener to the ImageView’s ViewTreeObserver.
2. Inside the onPreDraw() method, obtain the width and height using getWidth() and getHeight().
3. Remember to remove the listener after obtaining the dimensions to avoid unnecessary calls.

imageView.getViewTreeObserver().addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() { @Override public boolean onPreDraw() { imageView.getViewTreeObserver().removeOnPreDrawListener(this); int width = imageView.getWidth(); int height = imageView.getHeight(); // Use width and height here return true; } }); 

Leveraging onGlobalLayoutListener

The onGlobalLayoutListener, another option accessible through the ViewTreeObserver, provides similar functionality. This listener is called whenever a change occurs in the layout of the entire view hierarchy containing the ImageView. This can be useful if you need to respond to dynamic layout adjustments.

While onGlobalLayoutListener can be effective, it’s important to be mindful of its broader scope. It triggers more frequently than onPreDrawListener, potentially leading to performance issues if not used carefully. Prefer onPreDrawListener if you only need the initial dimensions.

Post-Layout Calculations with post()

The post() method offers a simpler alternative for retrieving dimensions after the layout is complete. It allows you to post a Runnable to the message queue, which gets executed after the view is laid out. This method is particularly useful when working within the activity or fragment lifecycle.

imageView.post(new Runnable() { @Override public void run() { int width = imageView.getWidth(); int height = imageView.getHeight(); // Use width and height here } }); 

Handling Images Loaded from URLs

When loading images from URLs using libraries like Glide or Picasso, the ImageView dimensions might not be available immediately because the image loading is asynchronous. In these cases, use a listener provided by the image loading library to determine when the image is loaded and then get the ImageView’s dimensions.

Glide.with(context) .load("your_image_url") .into(new SimpleTarget<Drawable>() { @Override public void onResourceReady(@NonNull Drawable resource, @Nullable Transition<? super Drawable> transition) { imageView.setImageDrawable(resource); int width = imageView.getWidth(); int height = imageView.getHeight(); // Use width and height here } }); 

FAQ

Q: Why does getWidth() return 0 initially?

A: The layout process hasn’t completed yet, so the dimensions are not calculated.

Understanding the Android layout lifecycle is essential for obtaining accurate ImageView dimensions. By utilizing techniques like onPreDrawListener, onGlobalLayoutListener, or post(), you can ensure you’re accessing these values at the correct time. Remember to consider the specific context of your implementation and choose the method that best suits your needs. Using these approaches will help you avoid common pitfalls and build more robust and responsive Android applications. For more advanced layout techniques, check out Android’s documentation on declaring layouts.

Learn MoreQuestion & Answer :

╔══════════════════════════════════════════════╗ ^ ║ ImageView ╔══════════════╗ ║ | ║ ║ ║ ║ | ║ ║ Actual image ║ ║ | ║ ║ ║ ║ |60px height of ImageView ║ ║ ║ ║ | ║ ║ ║ ║ | ║ ╚══════════════╝ ║ | ╚══════════════════════════════════════════════╝ <------------------------------------------------> 90px width of ImageView 

I have an image view with some default height and width, images are stored in db and I want to scale Image according to Imageview height width. As I don’t want it give default values because when ever I change it’s height and width I also have to change it in code.

I am trying to get the height and width of ImageView but 0 is returned to me in both cases.

int height = ((ImageView) v.findViewById(R.id.img_ItemView)).getHeight(); 

this returns me 0 even it has default height and width

My answer on this question might help you:

int finalHeight, finalWidth; final ImageView iv = (ImageView)findViewById(R.id.scaled_image); final TextView tv = (TextView)findViewById(R.id.size_label); ViewTreeObserver vto = iv.getViewTreeObserver(); vto.addOnPreDrawListener(new ViewTreeObserver.OnPreDrawListener() { public boolean onPreDraw() { iv.getViewTreeObserver().removeOnPreDrawListener(this); finalHeight = iv.getMeasuredHeight(); finalWidth = iv.getMeasuredWidth(); tv.setText("Height: " + finalHeight + " Width: " + finalWidth); return true; } }); 

You can then add your image scaling work from within the onPreDraw() method.