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Form Stuff

This tutorial introduces a variety of widgets that are useful when creating forms, such as image buttons, text fields, checkboxes and radio buttons.

  1. Start a new project named HelloFormStuff.
  2. Your res/layout/main.xml file should already have a basic LinearLayout: 
    <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >
</LinearLayout>

    For each widget you want to add, just put the respective View inside this LinearLayout.

Each section below also assumes that your HelloFormStuff Activity has the following default implementation of the onCreate() method:

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
}

Now select which kind of form widget you'd like to create:

Custom Button

In this section, you will create a button with a custom image instead of text, using the Button widget and an XML file that defines three different images to use for the different button states. When the button is pressed, a short message will be displayed.

  1. Copy the images on the right into the res/drawable/ directory of your project. These will be used for the different button states.
  2. Create a new file in the res/drawable/ directory named android_button.xml. Insert the following XML: 
    <?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@drawable/android_pressed"
          android:state_pressed="true" />
    <item android:drawable="@drawable/android_focused"
          android:state_focused="true" />
    <item android:drawable="@drawable/android_normal" />
</selector>

    This defines a single drawable resource, which will change its image based on the current state of the button. The first <item> defines android_pressed.png as the image when the button is pressed (it's been activated); the second <item> defines android_focused.png as the image when the button is focused (when the button is highlighted using the trackball or directional pad); and the third <item> defines android_normal.png as the image for the normal state (when neither pressed nor focused). This XML file now represents a single drawable resource and when referenced by a Button for its background, the image displayed will change based on these three states.

    Note: The order of the <item> elements is important. When this drawable is referenced, the <item>s are traversed in-order to determine which one is appropriate for the current button state. Because the "normal" image is last, it is only applied when the conditions android:state_pressed and android:state_focused have both evaluated false.

  3. Open the res/layout/main.xml file and add the Button element: 
        <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:padding="10dp"
        android:background="@drawable/android_button" />

    The android:background attribute specifies the drawable resource to use for the button background (which, when saved at res/drawable/android.xml, is referenced as @drawable/android). This replaces the normal background image used for buttons throughout the system. In order for the drawable to change its image based on the button state, the image must be applied to the background.

  4. To make the button do something when pressed, add the following code at the end of the onCreate() method: 
    final Button button = (Button) findViewById(R.id.button);
button.setOnClickListener(new OnClickListener() {
    public void onClick(View v) {
        // Perform action on clicks
        Toast.makeText(HelloFormStuff.this, "Beep Bop", Toast.LENGTH_SHORT).show();
    }
});

    This captures the Button from the layout, then adds an View.OnClickListener. The View.OnClickListener must implement the onClick(View) callback method, which defines the action to be made when the button is clicked. In this example, a Toast message will be displayed.

  5. Now run the application.

Edit Text

In this section, you will create a text field for user input, using the EditText widget. Once text has been entered into the field, the "Enter" key will display the text in a toast message.

  1. Open the res/layout/main.xml file and add the EditText element (inside the LinearLayout): 
        <EditText
        android:id="@+id/edittext"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"/>
  2. To do something with the text that the user types, add the following code to the end of the onCreate() method: 
    final EditText edittext = (EditText) findViewById(R.id.edittext);
edittext.setOnKeyListener(new OnKeyListener() {
    public boolean onKey(View v, int keyCode, KeyEvent event) {
        // If the event is a key-down event on the "enter" button
        if ((event.getAction() == KeyEvent.ACTION_DOWN) &&
            (keyCode == KeyEvent.KEYCODE_ENTER)) {
          // Perform action on key press
          Toast.makeText(HelloFormStuff.this, edittext.getText(), Toast.LENGTH_SHORT).show();
          return true;
        }
        return false;
    }
});

    This captures the EditText element from the layout and adds an View.OnKeyListener. The View.OnKeyListener must implement the onKey(View, int, KeyEvent) method, which defines the action to be made when a key is pressed while the widget has focus. In this case, the method is defined to listen for the Enter key (when pressed down), then pop up a Toast message with the text that has been entered. The onKey(View, int, KeyEvent) method should always return true if the event has been handled, so that the event doesn't bubble-up (which would result in a carriage return in the text field).

  3. Run the application.

Checkbox

In this section, you will create a checkbox for selecting items, using the CheckBox widget. When the checkbox is pressed, a toast message will indicate the current state of the checkbox.

  1. Open the res/layout/main.xml file and add the CheckBox element (inside the LinearLayout): 
        <CheckBox android:id="@+id/checkbox"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="check it out" />
  2. To do something when the state is changed, add the following code to the end of the onCreate() method: 
    final CheckBox checkbox = (CheckBox) findViewById(R.id.checkbox);
checkbox.setOnClickListener(new OnClickListener() {
    public void onClick(View v) {
        // Perform action on clicks, depending on whether it's now checked
        if (((CheckBox) v).isChecked()) {
            Toast.makeText(HelloFormStuff.this, "Selected", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(HelloFormStuff.this, "Not selected", Toast.LENGTH_SHORT).show();
        }
    }
});

    This captures the CheckBox element from the layout, then adds an View.OnClickListener. The View.OnClickListener must implement the onClick(View) callback method, which defines the action to be made when the checkbox is clicked. When clicked, isChecked() is called to check the new state of the check box. If it has been checked, then a Toast displays the message "Selected", otherwise it displays "Not selected". Note that the View object that is passed in the onClick(View) callback must be cast to a CheckBox because the isChecked() method is not defined by the parent View class. The CheckBox handles its own state changes, so you only need to query the current state.

  3. Run it.

Tip: If you need to change the state yourself (such as when loading a saved CheckBoxPreference), use the setChecked(boolean) or toggle() method.

Radio Buttons

In this section, you will create two mutually-exclusive radio buttons (enabling one disables the other), using the RadioGroup and RadioButton widgets. When either radio button is pressed, a toast message will be displayed.

  1. Open the res/layout/main.xml file and add two RadioButtons, nested in a RadioGroup (inside the LinearLayout): 
        <RadioGroup
      android:layout_width="fill_parent"
      android:layout_height="wrap_content"
      android:orientation="vertical">
      <RadioButton android:id="@+id/radio_red"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="Red" />
      <RadioButton android:id="@+id/radio_blue"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="Blue" />
    </RadioGroup>

    It's important that the RadioButtons are grouped together by the RadioGroup element so that no more than one can be selected at a time. This logic is automatically handled by the Android system. When one RadioButton within a group is selected, all others are automatically deselected.

  2. To do something when each RadioButton is selected, you need an View.OnClickListener. In this case, you want the listener to be re-usable, so add the following code to create a new member in the HelloFormStuff Activity: 
    private OnClickListener radio_listener = new OnClickListener() {
    public void onClick(View v) {
        // Perform action on clicks
        RadioButton rb = (RadioButton) v;
        Toast.makeText(HelloFormStuff.this, rb.getText(), Toast.LENGTH_SHORT).show();
    }
};

    First, the View that is passed to the onClick(View) method is cast into a RadioButton. Then a Toast message displays the selected radio button's text.

  3. Now, at the bottom of the onCreate() method, add the following: 
      final RadioButton radio_red = (RadioButton) findViewById(R.id.radio_red);
  final RadioButton radio_blue = (RadioButton) findViewById(R.id.radio_blue);
  radio_red.setOnClickListener(radio_listener);
  radio_blue.setOnClickListener(radio_listener);

    This captures each of the RadioButtons from the layout and adds the newly-created View.OnClickListener to each.

  4. Run the application.

Tip: If you need to change the state yourself (such as when loading a saved CheckBoxPreference), use the setChecked(boolean) or toggle() method.

Toggle Button

In this section, you'll create a button used specifically for toggling between two states, using the ToggleButton widget. This widget is an excellent alternative to radio buttons if you have two simple states that are mutually exclusive ("on" and "off", for example).

  1. Open the res/layout/main.xml file and add the ToggleButton element (inside the LinearLayout): 
        <ToggleButton android:id="@+id/togglebutton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textOn="Vibrate on"
        android:textOff="Vibrate off"/>

    The attributes android:textOn and android:textOff specify the text for the button when the button has been toggled on or off. The default values are "ON" and "OFF".

  2. To do something when the state is changed, add the following code to the end of the onCreate() method: 
    final ToggleButton togglebutton = (ToggleButton) findViewById(R.id.togglebutton);
togglebutton.setOnClickListener(new OnClickListener() {
    public void onClick(View v) {
        // Perform action on clicks
        if (togglebutton.isChecked()) {
            Toast.makeText(HelloFormStuff.this, "Checked", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(HelloFormStuff.this, "Not checked", Toast.LENGTH_SHORT).show();
        }
    }
});

    This captures the ToggleButton element from the layout, then adds an View.OnClickListener. The View.OnClickListener must implement the onClick(View) callback method, which defines the action to perform when the button is clicked. In this example, the callback method checks the new state of the button, then shows a Toast message that indicates the current state.

    Notice that the ToggleButton handles its own state change between checked and unchecked, so you just ask which it is.

  3. Run the application.

Tip: If you need to change the state yourself (such as when loading a saved CheckBoxPreference), use the setChecked(boolean) or toggle() method.

Rating Bar

In this section, you'll create a widget that allows the user to provide a rating, with the RatingBar widget.

  1. Open the res/layout/main.xml file and add the RatingBar element (inside the LinearLayout): 
        <RatingBar android:id="@+id/ratingbar"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:numStars="5"
        android:stepSize="1.0"/>

    The android:numStars attribute defines how many stars to display for the rating bar. The android:stepSize attribute defines the granularity for each star (for example, a value of 0.5 would allow half-star ratings).

  2. To do something when a new rating has been set, add the following code to the end of the onCreate() method: 
    final RatingBar ratingbar = (RatingBar) findViewById(R.id.ratingbar);
ratingbar.setOnRatingBarChangeListener(new OnRatingBarChangeListener() {
    public void onRatingChanged(RatingBar ratingBar, float rating, boolean fromUser) {
        Toast.makeText(HelloFormStuff.this, "New Rating: " + rating, Toast.LENGTH_SHORT).show();
    }
});

    This captures the RatingBar widget from the layout with findViewById(int) and then sets an RatingBar.OnRatingBarChangeListener. The onRatingChanged() callback method then defines the action to perform when the user sets a rating. In this case, a simple Toast message displays the new rating.

  3. Run the application.

If you've added all the form widgets above, your application should look like this:

References

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