Contents of My Android experience in February 2017
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_test1) {
Toast.makeText(this, "in test1", Toast.LENGTH_LONG).show();
return true;
}
if (id == R.id.action_test2) {
TextView tv = (TextView)findViewById(R.id.textview);
String s = tv.getText().toString();
Toast.makeText(this, "s = " + s, Toast.LENGTH_LONG).show();
tv.setText("updated");
return true;
}
return super.onOptionsItemSelected(item);
}
note-1: After you type Toast, hit enter, you'll see android.widget ,
hit again to import the library.
note-2: In Android, a view is a ui control, like TextView.
note-3: In this demo, you can see to interact with a view.
note-4: Toast is like alert in javascript, easy for debug.
note-5: You can use java switch language construct. That is not a must.
note-6: You can set a text in a strings.xml. That is not a must. You can take care later.
Some rest services provides data, not as an array.
if (id == R.id.action_test3) {
JSONObject obj;
// {dogs: [{"name":"Tairo","weight":28},{"name":"Emi","weight":30}]}
String content = "{dogs: [{\"name\":\"Tairo\",\"weight\":28},{\"name\":\"Emi\",\"weight\":30}]}";
try {
obj = new JSONObject(content);
JSONArray ar = obj.getJSONArray("dogs");
int num = ar.length();
String strNum = Integer.toString(num);
Toast.makeText(this, "number of dogs is " + strNum, Toast.LENGTH_LONG).show();
} catch (JSONException e) {
Toast.makeText(this, "convert to JSONObject is bad", Toast.LENGTH_LONG).show();
e.printStackTrace();
}
return true;
}
private String dogName;
private int dogWeight;
Dog dog1 = new Dog();
dog1.setDogName("Tairo");
dog1.setDogWeight(28);
String name = dog1.getDogName();
int weight = dog1.getDogWeight();
Toast.makeText(this, name + weight, Toast.Length_LONG().show();
// Concatenatin a String with a integer, results in a String.
in AndroidManifest.xml, add the following code before app tag.
in MainActivity.java, add a instance helper method as below:
protected boolean isOnline(){
ConnectivityManager cm
= (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo netInfo = cm.getActiveNetworkInfo();
if (netInfo != null && netInfo.isConnectedOrConnecting()){
return true;
} else {
return false;
}
}
// create a instance variable as below:
private String uri = "http://www.mj-go-test.com/test_6_select.php";
// in onCreate, modifying the code as below
.....
if (isOnline()) {
MyTask task = new MyTask();
task.execute(uri);
Toast.makeText(this, "network is available", Toast.LENGTH_LONG).show();
} else {
Toast.makeText(this, "network isn't available", Toast.LENGTH_LONG).show();
}
}
package com.example.peterkao.app02272017;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
public class HttpHelper {
public static String getData(String uri){
BufferedReader reader = null;
try {
URL url = new URL(uri);
HttpURLConnection con = (HttpURLConnection) url.openConnection();
StringBuilder sb = new StringBuilder();
reader = new BufferedReader(new InputStreamReader(con.getInputStream()));
String line;
while ((line = reader.readLine()) != null){
sb.append(line + "\n");
}
return sb.toString();
} catch (Exception e) {
e.printStackTrace();
return null;
} finally {
if (reader != null){
try {
reader.close();;
} catch (IOException e){
e.printStackTrace();
return null;
}
}
}
}
}
private class MyTask extends AsyncTask{
@Override
protected String doInBackground(String... params){
String contents = "";
try {
contents = HttpHelper.getData(params[0]);
} catch (Exception e) {
e.printStackTrace();
}
return contents;
}
@Override
protected void onPostExecute(String result) {
TextView tv = (TextView)findViewById(R.id.tv);
tv.setText(result);
}
}
in MainActivity, code the menu item handler
if (online()){
MyTask = new MyTask();
task.execute();
} else {
// output error
}
private class MyTask extends AsyncTask {
@Override
protected String doInBackground(String... p) {
BufferedReader reader = null;
try {
//-------- 1. post ----------------------
String strUri = "http://www.mj-go-test.com/post_echoback.php";
URL url = new URL(strUri);
HttpURLConnection con = (HttpURLConnection) url.openConnection();
con.setRequestMethod("POST");
JSONObject obj = new JSONObject();
obj.put("weight", new Integer(29));
obj.put("name", "Emi kao");
String myData = "params = " + obj.toString();
con.setDoOutput(true);
OutputStreamWriter writer = new OutputStreamWriter(con.getOutputStream());
writer.write(myData);
writer.flush();
//-------- 2. get the echo data back from the service -----------
StringBuilder sb = new StringBuilder();
reader = new BufferedReader(new InputStreamReader(con.getInputStream()));
String line;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
return sb.toString();
//-------- end --------------------------------------
//return "post and get done";
} catch (Exception e) {
e.printStackTrace();
return null;
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
e.printStackTrace();
return null;
}
}
}
}
@Override
protected void onPostExecute(String result) {
Toast.makeText(MainActivity.this, result, Toast.LENGTH_SHORT).show();
}
} //---------------------- end of inner class