Hello Friends,
This is the third article in this series. In this article we will extend the HelloWorld app a little more. We will add text boxes and will fetch the data from those text boxes, just like web forms.
If you havn't gone through previous article I recommend to do so. These articles are very simple ans small and should not take more than 10 minutes.
Lets start by adding edit box which will accept email address and another edit box which will take password as input from user.
Then add a button on click of which we will collect the data from edit boxes and will display on a text box.
Edit box contains the editable text while text on a text-box can not be edit directly by user. Any such text has to be manipulated through programming.
To achieve what we said above we will need to add code to activity_main.xml file. After adding the code our file will look like below.
1: <RelativeLayout
2: xmlns:android="http://schemas.android.com/apk/res/android"
3: xmlns:tools="http://schemas.android.com/tools"
4: android:layout_width="match_parent"
5: android:layout_height="match_parent"
6: android:paddingLeft="@dimen/activity_horizontal_margin"
7: android:paddingRight="@dimen/activity_horizontal_margin"
8: android:paddingTop="@dimen/activity_vertical_margin"
9: android:paddingBottom="@dimen/activity_vertical_margin"
10: tools:context=".MainActivity">
11:
12: <LinearLayout
13: android:layout_width="match_parent"
14: android:layout_height="match_parent"
15: android:orientation="vertical">
16:
17: <TextView android:text="@string/signin"
18: android:layout_width="match_parent"
19: android:layout_height="wrap_content"
20: android:textSize="20dp"
21: android:textColor="@android:color/background_dark"
22: android:gravity="center"
23: android:padding="10dp"/>
24:
25: <EditText
26: android:id="@+id/email"
27: android:layout_width="match_parent"
28: android:layout_height="wrap_content"
29: android:padding="10dp"
30: android:hint="Email"
31: android:inputType="textEmailAddress"/>
32:
33: <EditText
34: android:id="@+id/password"
35: android:layout_width="match_parent"
36: android:layout_height="wrap_content"
37: android:padding="10dp"
38: android:hint="Password"
39: android:inputType="textWebPassword"/>
40:
41: <Button
42: android:layout_width="match_parent"
43: android:layout_height="wrap_content"
44: android:text="@string/login"
45: android:background="@android:color/holo_blue_dark"
46: android:onClick="getEmailAndPassword"
47: android:layout_margin="10dp"/>
48:
49: <TextView
50: android:id="@+id/result"
51: android:layout_width="match_parent"
52: android:layout_height="wrap_content"
53: android:text="@string/result"
54: android:gravity="center"
55: android:textSize="15dp"/>
56:
57: </LinearLayout>
58: </RelativeLayout>
When you type this code in xml file, you can see the preview of activity in preview pane on right side.
We will read more about Layouts in upcoming articles.
We defined ID for each view in above xml. ID is required to access and manipulate that view from program. Every view should have unique Id.
Width and height parameter may take any of the below value -
match_parent : fill the parent view completely.
wrap_content : Occupy space required to keep the content e.g. text within itself.
DP : we can define width with some integer value. dp, in, px, pt are different such units. Always use DP when building application for multiple screens.
Hint parameter works as placeholder in web. It displays a hint in the edit box and as soon as user starts typing it vanishes away.
InputType parameter restrict the input content. If number is selected than only numbers can be entered in that edit box. Setting input-type save us the effort of validating the input text. Explore the more values that can be set for input-type parameter.
We can call a function on click of a button. Name of the to be called function is defined in onClick parameter of button view.
We do not write any string literal directly in this layout xml file. All such strings are defined in res/values/strings.xml file
Gravity parameter defines the alignment of text in that view. Apart from center it can takes left and right as values.
If you wants to know about any other parameter than please comment in the comment section.
Strings.xml
1: <resources>
2: <string name="app_name">HelloWorld</string>
3:
4: <string name="hello_world">Hello world!</string>
5: <string name="action_settings">Settings</string>
6:
7: <string name="login">Login</string>
8: <string name="signin">Sign In</string>
9: <string name="result">Result will appear here.</string>
10: </resources>
Now lets see how to access the data in code.
ActivityMain.java
1: package mycompany.helloworld;
2:
3: import android.support.v7.app.AppCompatActivity;
4: import android.os.Bundle;
5: import android.view.Menu;
6: import android.view.MenuItem;
7: import android.view.View;
8: import android.widget.EditText;
9: import android.widget.TextView;
10:
11: import org.w3c.dom.Text;
12:
13: public class MainActivity extends AppCompatActivity {
14:
15: @Override
16: protected void onCreate(Bundle savedInstanceState) {
17: super.onCreate(savedInstanceState);
18: setContentView(R.layout.activity_main);
19:
20: }
21:
22: public void getEmailAndPassword(View view) {
23: String email = getEmail();
24: String password = getPassword();
25: displayResult(email,password);
26: }
27:
28: public String getEmail() {
29: EditText editText = (EditText)findViewById(R.id.email);
30: String email = editText.getText().toString();
31: return email;
32: }
33:
34: public String getPassword() {
35: EditText editText = (EditText)findViewById(R.id.password);
36: String password = editText.getText().toString();
37: return password;
38: }
39:
40: public void displayResult(String email, String password) {
41: String result = "Entered Email : "+ email + "\n";
42: result = result+ "Entered Password : "+password;
43: TextView tv = (TextView) findViewById(R.id.result);
44: tv.setText(result);
45: }
46:
47: @Override
48: public boolean onCreateOptionsMenu(Menu menu) {
49: // Inflate the menu; this adds items to the action bar if it is present.
50: getMenuInflater().inflate(R.menu.menu_main, menu);
51: return true;
52: }
53:
54: @Override
55: public boolean onOptionsItemSelected(MenuItem item) {
56: // Handle action bar item clicks here. The action bar will
57: // automatically handle clicks on the Home/Up button, so long
58: // as you specify a parent activity in AndroidManifest.xml.
59: int id = item.getItemId();
60:
61: //noinspection SimplifiableIfStatement
62: if (id == R.id.action_settings) {
63: return true;
64: }
65:
66: return super.onOptionsItemSelected(item);
67: }
68: }
In the snapshot below you can see if some keyword is not found by the IDE then it show the warning. We can correct these errors by including relevant packages. Just press the Alt+enter and required package will be imported.
When you run the application [How to run application] on your device, following screen will appear. Enter the text and press the 'Login' button.
On click of 'Login' Button getEmailAndPassword function is called which in turn call other functions and display the result.
In the next article we will see how to transfer the data between two activities.
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