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Android Handler
Android Source Code
Java program for surveillance using an Android smartphone. Webcam with FTP access to the photo storage.
Android Safety SYSTEM >>
With Handler you can send messages to TextView
Handler allows you to put messages in the queue and is able to process them itself. The trick here is that he can put a message from one stream, and read it from another.
This allows you to make a very useful function - displaying telemetry - the parameters necessary for debugging a finished application without Android Studio and for finding the causes of malfunctions in the monitoring system.
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
tvStatus = (TextView) findViewById(R.id.tvStatus);
pbConnect = (ProgressBar) findViewById(R.id.pbConnect);
btnConnect = (Button) findViewById(R.id.btnConnect);
h = new Handler() {
public void handleMessage(android.os.Message msg) {
switch (msg.what) {
case STATUS_NONE:
btnConnect.setEnabled(true);
tvStatus.setText("Not connected");
break;
case STATUS_CONNECTING:
btnConnect.setEnabled(false);
pbConnect.setVisibility(View.VISIBLE);
tvStatus.setText("Connecting");
break;
case STATUS_CONNECTED:
pbConnect.setVisibility(View.GONE);
tvStatus.setText("Connected");
break;
}
};
};
h.sendEmptyMessage(STATUS_NONE);
}
STATUS_NONE, STATUS_CONNECTING, STATUS_CONNECTED are status constants. We will pass them in the message, in the what attribute.
In onCreate, we create a Handler and implement its handleMessage method. This method is responsible for handling messages that are intended for this Handler. Accordingly, a message is sent to the method input - Message. We read the what attribute and, depending on the connection status, change the screen:
STATUS_NONE - no connection. The connection button is active, the TextView reflects the connection status.
STATUS_CONNECTING - in the process of connecting. The connection button is inactive, we show the ProgressBar, the TextView reflects the connection status.
In onCreate, after creating the Handler, we immediately send it a message with the STATUS_NONE status. For this we use the sendEmptyMessage method. In this method, a message is created, its what attribute is filled (with the value we pass to sendEmptyMessage), the Handler is set as the destination, and the message is sent to the queue.
In the onclick method, we create and start a new thread. In it, we, using sleep, emulate the process of connecting to the server, doing work and disconnecting. And, as the actions are performed, we send messages with statuses for the Handler. Those. it turns out that after pressing the Connect button, the status changes to STATUS_CONNECTING, the connection goes on for two seconds, the status changes to STATUS_CONNECTED, the actions are performed for 3 seconds and the status changes to STATUS_NONE.
public void onclick(View v) {
Thread t = new Thread(new Runnable() {
public void run() {
try {
// устанавливаем подключение
h.sendEmptyMessage(STATUS_CONNECTING);
TimeUnit.SECONDS.sleep(2);
// установлено
h.sendEmptyMessage(STATUS_CONNECTED);
// выполняется какая-то работа
TimeUnit.SECONDS.sleep(3);
// разрываем подключение
h.sendEmptyMessage(STATUS_NONE);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
t.start();
}
You can do TextView with scrolling text on a free part of the application screen. And add important messages there, which, when debugging a program in Android Studio, you could display in the debug window.
For example, a smartphone with an app cannot upload a photo to your webserver. Telemetry displays messages about the start of connection to FTP server, but no message about successful connection. Then you need to check your smartphone - that data transmission over the Internet is allowed. Another reason is the wrong FTP server address or password / login
If everything is correct here, then perhaps you did not specify the address of the folder for downloading the image, or you specified it incorrectly.
In one of the sections of the manual, we will write more about telemetry.
Android Handler
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