Conversion between Message and String in android?

android, handler, java, multithreading, network-programming

Solution

You don't have to overload or try to do any coversions between `String` and `Message`. What you should do, is to put that String into an object of type Message and sent it to the `Handler`. Then in `handleMessage()` extract the String from the Message.

Something like this:

// ....
String message = "linkSpeed = " + linkSpeed;
Message msg = Message.obtain(); // Creates an new Message instance
msg.obj = message; // Put the string into Message, into "obj" field.
msg.setTarget(handler); // Set the Handler
msg.sendToTarget(); //Send the message
//....

And in `handleMessage()`:

@Override
public void handleMessage(Message msg) {
    String message = (String) msg.obj; //Extract the string from the Message
    textView.setText(message);
    //....
}

But besides this, the program has an issue: you won't be able to send the data to the handler because that part of the code is unreachable:

while (true) {
    WifiInfo s = wifiManager.getConnectionInfo();
    //..
}
String message = "linkSpeed = " + linkSpeed; // This line never won't be reached.

Also, don't forget to stop the `Thread` at some time, otherwise it will continue to run even after the app is closed.

Problem

I'm trying to monitor network connectivity on android. This cannot be done on the main thread, so the data collection occurs on a separate thread I spawn - and I'm learning to use the Handler class to report back to the UI every second. Here's the relevant snippets of my code... ``` public class MainActivity extends Activity { private TextView textView; private int linkSpeed; Handler handler = new Handler() { @Override public void handleMessage(Message msg) { Message message = msg; textView.setText(message); setContentView(textView); } }; /** Called when the activity is created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); textView = new TextView(this); textView.setTextSize(25); Thread thread = new Thread() { public void run() { for (;;) { try { WifiManager wifiManager = (WifiManager) getSystemService(Context.WIFI_SERVICE); while (true) { WifiInfo wifiInfo = wifiManager.getConnectionInfo(); if (wifiInfo != null) { linkSpeed = wifiInfo.getLinkSpeed(); //measured using WifiInfo.LINK_SPEED_UNITS } else { linkSpeed = -1; } } String message = "linkSpeed = " + linkSpeed; handler.handleMessage(message); Thread.sleep(1000); } catch (Exception e) { e.printStackTrace(); } } } }; thread.start(); } ``` The problem is, the message I get from the new thread I spawn is of type "String", but I cannot seem to overload the handleMessage method in the Handler class to take Strings instead of Messages. I don't think there's a direct conversion between Strings and Messages, as the only method in the Message class that returns a String is the toString() method, but it returns a description, rather than what the message contains. I'm also confused as to how I can convert a String to a Message - and I feel like I'm doing a very roundabout approach. Any help would be greatly appreciated!

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