Nilanchala Panigrahy

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This example is an improved version of my previous example Android GridView Example. Instead of using static images to display the grid items, let's make this example more realistic by downloading the data in real-time from the server and rendering the grid items. The following video depicts the output of this example. Without wasting much time, let us jump straight into what it takes to build this kind of GridView. You need to follow the following steps to complete this example. 1. Add GridView in Activity Layout First, create a new android project. For this example, I prefer to use Android Studio. Create a new layout file to your project res/layout folder and name it as activity_grid_view.xml. And add the following code blocks. The above layout is pretty straightforward. We have declared an GridView and a ProgressBar in activity layout. The progress bar will be displayed when the data is downloaded. 2. Declare GridView Item Layout Let us now add another file named grid_item_layout.xml to res/layout folder. This layout will be used by a custom grid adapter for laying out individual grid items. For the sake of simplicity, we are adding an ImageView and a TextView. 3. Adding Internet Permission You might be aware that, the Android application must declare all the permissions that are required for the application. As we need to download the data from the server, we need to add INTERNET permission. Add the following line to AndroidManifest.xml the file. Notice that we have also declared all the activities used in the application. 4. Adding Picasso Image Downloading Library Android open-source developer community brings some interesting libraries that can be integrated easily into Android applications. They serve a great deal of purpose and save a lot of time. Here in this example, I am talking about Picasso the image-loading library. We will add the Picasso library for downloading and caching images. Visit here to learn more about how to use the Picasso library on Android. You can add the Picasso library by adding the following dependency to the build.gradle file. dependencies { compile fileTree(dir: 'libs', include: ['*.jar']) compile 'com.android.support:appcompat-v7:21.0.3' compile 'com.squareup.picasso:picasso:2.5.2' } 5. Create a GridView Custom Adapter A grid view is an adapter view. It requires an adapter to render the collection of data items. Add a new class named GridViewAdapter.java to your project and add the following code snippets. package com.javatechig.gridviewexample; import java.util.ArrayList; import android.app.Activity; import android.content.Context; import android.text.Html; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.ArrayAdapter; import android.widget.ImageView; import android.widget.TextView; import com.squareup.picasso.Picasso; public class GridViewAdapter extends ArrayAdapter { private Context mContext; private int layoutResourceId; private ArrayList mGridData = new ArrayList(); public GridViewAdapter(Context mContext, int layoutResourceId, ArrayList mGridData) { super(mContext, layoutResourceId, mGridData); this.layoutResourceId = layoutResourceId; this.mContext = mContext; this.mGridData = mGridData; } /** * Updates grid data and refresh grid items. * @param mGridData */ public void setGridData(ArrayList mGridData) { this.mGridData = mGridData; notifyDataSetChanged(); } @Override public View getView(int position, View convertView, ViewGroup parent) { View row = convertView; ViewHolder holder; if (row == null) { LayoutInflater inflater = ((Activity) mContext).getLayoutInflater(); row = inflater.inflate(layoutResourceId, parent, false); holder = new ViewHolder(); holder.titleTextView = (TextView) row.findViewById(R.id.grid_item_title); holder.imageView = (ImageView) row.findViewById(R.id.grid_item_image); row.setTag(holder); } else { holder = (ViewHolder) row.getTag(); } GridItem item = mGridData.get(position); holder.titleTextView.setText(Html.fromHtml(item.getTitle())); Picasso.with(mContext).load(item.getImage()).into(holder.imageView); return row; } static class ViewHolder { TextView titleTextView; ImageView imageView; } } Notice the following in the above code snippets, The setGridData() method updates the data display on GridView. The Picasso.with().load() the method is used to download the image from the URL and display it on the image view. The GridViewAdapter class constructor requires the id of the grid item layout and the list of data to operate on. You might be surprised, where the GridItem class came from. It's not magic, we need to add GridItem.java class to our project. The GridItem class looks as follows. 6. Download Data and Hook it to the Activity Now we will be heading towards hooking the adapter to GridView and making it functional. Create a new Java class and name it as GridViewActivity.java and perform the following steps. Override the onCreate() method and set the layout by calling setContentView() method Initialize the GridView and ProgressBar components by using their declared layout id. Initialize the CustomGridView adapter bypassing the grid row layout id and the list of GridItem objects. Use AsyncTask to download data from the server, once the download is successful read the stream JSON response. Parse the JSON string into the list of GridItem objects. Once downloading and parsing is completed, in onPostExecute() callback update the UI elements. The following code does all the above steps as described. Add the following code to GridViewActivity class. import java.io.BufferedReader; import java.io.IOException; import java.io.InputStream; import java.io.InputStreamReader; import java.util.ArrayList; import android.content.Intent; import android.os.AsyncTask; import android.os.Bundle; import android.support.v7.app.ActionBarActivity; import android.util.Log; import android.view.View; import android.widget.AdapterView; import android.widget.GridView; import android.widget.ProgressBar; import android.widget.Toast; import org.apache.http.HttpResponse; import org.apache.http.client.HttpClient; import org.apache.http.client.methods.HttpGet; import org.apache.http.impl.client.DefaultHttpClient; import org.json.JSONArray; import org.json.JSONException; import org.json.JSONObject; public class GridViewActivity extends ActionBarActivity { private static final String TAG = GridViewActivity.class.getSimpleName(); private GridView mGridView; private ProgressBar mProgressBar; private GridViewAdapter mGridAdapter; private ArrayList mGridData; private String FEED_URL = "http://javatechig.com/?json=get_recent_posts&count=45"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_gridview); mGridView = (GridView) findViewById(R.id.gridView); mProgressBar = (ProgressBar) findViewById(R.id.progressBar); //Initialize with empty data mGridData = new ArrayList<>(); mGridAdapter = new GridViewAdapter(this, R.layout.grid_item_layout, mGridData); mGridView.setAdapter(mGridAdapter); //Start download new AsyncHttpTask().execute(FEED_URL); mProgressBar.setVisibility(View.VISIBLE); } //Downloading data asynchronously public class AsyncHttpTask extends AsyncTask { @Override protected Integer doInBackground(String... params) { Integer result = 0; try { // Create Apache HttpClient HttpClient httpclient = new DefaultHttpClient(); HttpResponse httpResponse = httpclient.execute(new HttpGet(params[0])); int statusCode = httpResponse.getStatusLine().getStatusCode(); // 200 represents HTTP OK if (statusCode == 200) { String response = streamToString(httpResponse.getEntity().getContent()); parseResult(response); result = 1; // Successful } else { result = 0; //"Failed } } catch (Exception e) { Log.d(TAG, e.getLocalizedMessage()); } return result; } @Override protected void onPostExecute(Integer result) { // Download complete. Let us update UI if (result == 1) { mGridAdapter.setGridData(mGridData); } else { Toast.makeText(GridViewActivity.this, "Failed to fetch data!", Toast.LENGTH_SHORT).show(); } mProgressBar.setVisibility(View.GONE); } } String streamToString(InputStream stream) throws IOException { BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(stream)); String line; String result = ""; while ((line = bufferedReader.readLine()) != null) { result += line; } // Close stream if (null != stream) { stream.close(); } return result; } /** * Parsing the feed results and get the list * @param result */ private void parseResult(String result) { try { JSONObject response = new JSONObject(result); JSONArray posts = response.optJSONArray("posts"); GridItem item; for (int i = 0; i < posts.length(); i++) { JSONObject post = posts.optJSONObject(i); String title = post.optString("title"); item = new GridItem(); item.setTitle(title); JSONArray attachments = post.getJSONArray("attachments"); if (null != attachments && attachments.length() > 0) { JSONObject attachment = attachments.getJSONObject(0); if (attachment != null) item.setImage(attachment.getString("url")); } mGridData.add(item); } } catch (JSONException e) { e.printStackTrace(); } } } At this point, you will be able to run the app and notice that the app will download the data from the server and display it on GridView. 7. Handle GridView Click Event Right now GridView is not responding to user clicks. Let us make it more functional by adding the following code. mGridView.setOnItemClickListener(new AdapterView.OnItemClickListener() { public void onItemClick(AdapterView parent, View v, int position, long id) { //Get item at position GridItem item = (GridItem) parent.getItemAtPosition(position); //Pass the image title and url to DetailsActivity Intent intent = new Intent(GridViewActivity.this, DetailsActivity.class); intent.putExtra("title", item.getTitle()); intent.putExtra("image", item.getImage()); //Start details activity startActivity(intent); } }); When a user clicks on a grid item, we will start another activity that displays the full-screen image. You can start one activity from another by calling startActivity() method. We need to pass the details of the item such as the title, and image URL for displaying it on DetailsActivity. 8. Create Details Activity Layout Add a new layout file to res/layout directory, and name it as activity_details_view.xml and add the following code snippets. 9. Completing the Details Activity The DetailsActivity retrieves the details passed from GridViewActivity and renders the details on the screen. Create a new class named DetailsActivity and add the following code snippets. package com.javatechig.gridviewexample; import android.os.Bundle; import android.support.v7.app.ActionBar; import android.support.v7.app.ActionBarActivity; import android.text.Html; import android.widget.ImageView; import android.widget.TextView; import com.squareup.picasso.Picasso; public class DetailsActivity extends ActionBarActivity { private TextView titleTextView; private ImageView imageView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_details_view); ActionBar actionBar = getSupportActionBar(); actionBar.hide(); String title = getIntent().getStringExtra("title"); String image = getIntent().getStringExtra("image"); titleTextView = (TextView) findViewById(R.id.title); imageView = (ImageView) findViewById(R.id.grid_item_image); titleTextView.setText(Html.fromHtml(title)); Picasso.with(this).load(image).into(imageView); } } 10. Download the Complete Example Download from GitHub. 11. Custom Activity Transition in GridView Continue reading in our next tutorial.

Typically, events respond to user interactions. Android supports multiple ways to handle events on views. When a user clicks on an Android View, some method is getting called by the Android framework and then past the control to the application listeners. For example, when a user clicks on a view like as a button, the onTouchEvent() method is called on that button object. In order to make our application respond to the event, we must extend the class and override the method. But extending every View object in order to handle such an event would not be practical. Each View class in Android provides a collection of nested interfaces called listeners with callbacks that you can much more easily define in order to handle the event. 1. Defining a listener programatically on the OnCreate method button.setOnClickListener(new OnClickListener(){ @Override public void onClick(View v) { //do stuff } }); ? This method will create an anonymous class for each button you create. This is recommended only if you have fewer listeners in your class. But if we have a complex screen layout with many views, then writing a listener programatically for each view will make the code messy. It's costly and less readable. 2. Setting the android:OnClick property in XML ? Many people use this method of handling click events by writing an OnClick attribute in XML. But usually it is not preferable, because it is better to keep listeners inside the code. Internally, Android is using the Java reflection concept behind the scenes to handle this. It is less readable, and confuses some developers. 3. Implementing the OnClickListener interface on the Activity class and passing a reference to the Button public class MainActivity extends Activity implements OnClickListener{ @Override public void onClick(View v) { //do stuff } protected void onCreate(Bundle savedInstanceState) { ... button.setOnClickListener(this); } } Here, we are implementing the OnClickListener interface on the activity class and passing a self reference to the button. This way, the OnClick listener will hold the reference to the activity object, and is a heavy operation to keep the whole activity’s object in it. This way we can handle the click event for all views. However, we need to differentiate views using their IDs. We can use the view.getId() method to see which button was clicked. Again, this is preferable only when we have fewer views to handle. This way, all the click event handling codes are done in one place. This way is hard to navigate because you can’t determine the type of the listener you are using with the current button (I know Eclipse will highlight the methods this is pointing at, but with lots of code I think it will be hard to find). 4. Create a field with the OnClickListener type private OnClickListener onClickHandler = new OnClickListener(){ @Override public void onClick(View v) { //stuff } }; protected void onCreate(Bundle savedInstanceState) { ... button.setOnClickListener(onClickHandler); } ? The best practice is the create a local variable with the OnClickListener type. This way it is easy to navigate and more readable. But it doesn't stop you from implementing the other three options provided above. Everyone has different way of looking at the problem.

This example explains to display HTML in Android TextView. Many times while you design an application, you may encounter a place where you will like to use HTML content in your screen. This may be to display a static “eula” or “help” content. In android there is a lovely class android.text.HTML that processes HTML strings into displayable styled text. Currently android doesn’t support all HTML tags. Android API documentation does not stipulate what HTML tags are supported. I have looked into the android Source code and from a quick look at the source code, here’s what seems to be supported as of now. http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/2.2_r1.1/android/text/Html.java , , , , , , , , , , , , , , , , , , , , From HTML method returns displayable styled text from the provided HTML string. As per );"="" android’s official Documentations any tags in the HTML will display as a generic replacement image which your program can then go through and replace with real images. Html.formHtml method takes an Html.TagHandler and an Html.ImageGetter as arguments as well as the text to parse. We can parse null as for the Html.TagHandler but you’d need to implement your own Html.ImageGetter as there isn’t a default implementation. The Html.ImageGetterneeds to run synchronously and if you’re downloading images from the web you’ll probably want to do that asynchronously. But in my example I am using the images from resources to make my ImageGetter implementation simpler. package com.javatechig.example.ui; import android.os.Bundle; import android.app.Activity; import android.graphics.drawable.Drawable; import android.text.Html; import android.view.Menu; import android.widget.TextView; /* * @author: nilanchala * http://javatechig.com/ */ public class MainActivity extends Activity { private final String htmlText = " Heading TextThis tutorial " + "explains how to display " + "HTML text in android text view. " + "" + " Example from " + "Javatechig.com"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); TextView htmlTextView = (TextView)findViewById(R.id.html_text); htmlTextView.setText(Html.fromHtml(htmlText, new ImageGetter(), null)); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.main, menu); return true; } private class ImageGetter implements Html.ImageGetter { public Drawable getDrawable(String source) { int id; if (source.equals("hughjackman.jpg")) { id = R.drawable.hughjackman; } else { return null; } Drawable d = getResources().getDrawable(id); d.setBounds(0,0,d.getIntrinsicWidth(),d.getIntrinsicHeight()); return d; } }; }