Skip to content

Latest commit

 

History

History
140 lines (125 loc) · 7.15 KB

basicWidgets.md

File metadata and controls

140 lines (125 loc) · 7.15 KB

#Basic Android Widgets

Android defines many UI widgets, organized in a hierarchy; it helps to look at some of them, and at the basic hierarchy; notice that many attributes can be specified in xml and also in code; usually the mapping is easy.

The most used Android widgets are:

  • TextView, which represents a label, or any widget with text attached; this is the superclass of buttons and editviews.
  • EditText, which represents an editable text field. This is a subclass of TextView.
  • Button, which represents a simple button; since this has text, it is a subclass of TextView.
  • ImageButton, button with an image instead of text.
  • CompoundButton, buttons that can be checked or unchecked. Android provides 4 subclasses,Checkbox,ToggleButton, Switch, and RadioButton (RadioButtons belong to a RadioGroup, and only one is selected at any given time.

##Basic view parameters

  • all widgets inherit from View
  • can set background color (or image) with android:background
  • Use android:id to give your widget a name (accessed as R.id....)
  • need to specify android:layout_width and android:layout_height (can do other layout paraemeters)
    • match_parent (was fill_parent)
    • wrap_content
    • or specific widht in pixels, dp, %
  • every view has android:onClick
    <ImageView
        android:id="@+id/imageView1"
        android:layout_width="120dp"
        android:layout_height="120dp"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="29dp"
        android:src="@drawable/all_blue" 
        android:background="#00bb99"
        android:onClick="whacked"
	/>

##TextView and EditText

  • has android:text, getText,setText
    • notice text is NOT a string, but a CharSequence (which is a superclass of string), can use toString to convert to a string.
    • in xml, eclipse will complain if you use an actual string, since it wants you to use a reference (for internalization etc); we'll talk about those values later.
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />
  • EditText is editable
  • android:inputType controls which characters get accepted (and which keyboard gets displayed)
  • can use styles etc android:textAppearance="?android:attr/textAppearanceLarge"
  • can make multiline android:inputType="textMultiLine"
    <EditText
        android:id="@+id/editText1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceLarge"         
        android:background="#aa5555"
        android:maxLines="10"
        android:minLines="5"
        android:inputType="textMultiLine" >
        <requestFocus />
    </EditText>

Buttons

  • buttons are TextViews, so all of their attributes work for them
  • we normally use their onClick (although every view has onclick !)
  • buttons can have text and a pic with their android:drawableLeft attribute
  • we can use their android:onClick attribute, or set onClickListener in code
    <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        
        android:text="Full Screen Activity" 
        android:onClick="showFullScreenForm"
        android:drawableLeft="@drawable/whack"/>

##Compound Buttons (Checkboxes)

    <CheckBox
        android:id="@+id/checkBox1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="checkboxClicked"
        android:text="CheckBox" />

    <ToggleButton
        android:id="@+id/toggleButton1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="checkboxClicked"
        android:textOff="No"
        android:textOn="Yes" />
  • RadioButtons need to be embeded in a radio group; you can later ask if checked, or ask the group for the id of the button which is checked
    <RadioGroup
        android:id="@+id/radioGroup1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" 
        android:orientation="horizontal"
        >
        <RadioButton
            android:id="@+id/radio0"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:checked="true"
            android:text="Uno" />
	...
	</RadioGroup>

##Images

  • ImageView, which allows you to display an image
  • ImageButton, which is a button that displays an image instead of text.
  • Gallery, which is now deprecated, but widely used :) it displays a bunch of images and allows you to browse through them

##Other widgets

##Challenges

  1. Create an app that converts to/from decimal, binary, octal, hex. Java's Integer class has parseInt that takes a radix, and also toOctalString etc. Use radio buttons to decide what to convert from/to
  2. For an application of your choice, create a form, using as many different widgets as it makes sense.