03   layouts & ui design - Android
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  • 1. Workshop India
  • 2. » Information that defines what is drawn on the screen. ˃ stored as XML files in the /res/layout resource ˃ Simply a template for a User Interface on the screen.» A type of View class that can display other child controls or components. ˃ text controls ˃ buttons ˃ images
  • 3. What is a control? Any component that forms part of the screen.» Linear Layout ˃ It organizes controls linearly in either a vertical or horizontal fashion» Relative Layout, ˃ It organizes controls relative to one another, or to the parent control’s edges itself.» Table Layout ˃ A grid of made up of rows and columns, where a cell can display a view control» Frame Layout ˃ Frame layouts are the normal layout of choice when you want to overlap different views stacked on on top the other.
  • 4. » XML definitions are used for controlling how these layouts are » res/layout/main.xml is the layout definition for the main view. » setContentView(R.layout.main); for loading and displaying the selected layout.What is XML?eXtended Markup Language is a popular data exchange format
  • 5. » To separate Design from Development ˃ UI Designers (who concern themselves more with layout) ˃ Application Developers (who know Java and implement application functionality).» Complex controls (Also called views), like ListView or GridView, are usually populated with data programmatically» Recommended Practice: ˃ Creating an XML layout file for every screen that your application has ˃ Tying each screen to a specific activity
  • 6. XML and HTML? XML and HTML differ only in implementation as browser standards, XML is for arbitrary data and HTML is for Web Pages<name_of_tag property=“value”> <view01 android:property1=“val1”> </child01> <view02 android:property2=“val2”> </child02> <view03 android:property3=“val3”> </child03></name_of_tag >
  • 7. » Set up Controls with properties that are known at build time set in the XML layout files. ˃ All properties can be changed programmatically for dynamic application behaviour» Set up listeners for the controls: Views allow clients to set listeners that will be notified when something interesting happens to the view. ˃ Button exposes a listener to notify clients when the button is clicked.
  • 8. » Controls are child elements that can be presented to the user for Input/Output/Fanciness.» These controls are also called Widgets.» The design and initial values for the layout can be placed in the view.xml file in the /res/layout folder. <TextView android:text="RED" android:id="@+id/TextView01" android:layout_height="wrap_content" android:background="#f00" android:layout_width="fill_parent" android:layout_weight=".14" android:gravity="center" android:textColor="#000"></TextView>
  • 9. The following example adds two images to a relativelayout view.RelativeLayout rl = (RelativeLayout) findViewById(R.id.main);ImageView iv;RelativeLayout.LayoutParams params;iv = new ImageView(this);iv.setBackgroundColor(Color.YELLOW);params = new RelativeLayout.LayoutParams(30, 40);params.leftMargin = 50;params.topMargin = 60;rl.addView(iv, params);iv = new ImageView(this);iv.setBackgroundColor(Color.RED);params = new RelativeLayout.LayoutParams(30, 40);params.leftMargin = 80;params.topMargin = 90;rl.addView(iv, params);
  • 10. GenerateButton Property editor Tree View window Of Child Controls Preview Generated XML layout Of Layout
  • 11. » Separate Application to help design layouts and modify controls easily» Once done designing, click on generate and past the xml code into the required xml file.» All external resources other than layout.xml can also be generated here.
  • 12. » The linear layout works much as its name implies. ˃ it organizes controls linearly in either a vertical or horizontal fashion» Linear layouts can be defined within XML layout resources or programmatically in the application’s Java code.» DEMO : How to create the following layout in Droid Draw
  • 13. » In DroidDraw’s Widget Control Box, select text view and drop to the screen.» Change root-layout to LinearLayout.» In properties window, make the following changes and click apply: ˃ Id: @+id/text01 ˃ Width: fill_parent ˃ Height: 60dp ˃ Background color: Blue ˃ Padding: 5dp ˃ FontSize: 20sp ˃ Text: alignment: center
  • 14. » Make 4 such text views like this<?xml version="1.0" encoding="utf-8"?><LinearLayout android:id="@+id/widget32" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" xmlns:android="http://schemas.android.com/apk/res/android"><TextView android:id="@+id/widget41_copy" android:layout_width="fill_parent" android:layout_height="60dp" android:background="#ff3333ff" android:padding="5dp" android:text="TextView" android:hint="0" android:textSize="20sp" android:typeface="monospace" android:gravity="center" /><TextView android:id="@+id/widget41_copy"…..[continues]
  • 15. » To any one text view if the property control android:layout_weight=“1”Is given, that property with the highest value willtake up all remaining space in the screen.1 = 100% of remaining space.0.5 = 50% of remaining space.0.25 = 25% of remaining space.» android:layout_width="fill_parent”Makes that property all available space remainingin its parent container.» android:layout_width="wrap_content“Makes that property just as big as the contentinside it
  • 16. The layout weight property is used togive relative weights to the childcontrols of the Linear-Layout.I have 5 controls, 1/5 = 0.2So if I give 0.2 to all of themThey’ll allbe the same height!» And this behaviour will be the same in all android devices of different screen sizes.» Once you’ve made this layout in droid designer, click generate and copy the xml.
  • 17. » Make a new project» Open the main.xml file in /res/layout and paste the markup there.» See if the same thing Is generated in the dynamic preview.» Hit Run and open an AVD to see the application running.
  • 18. » The text for the UI layouts is stored seperately in a strings.xml file.» Enter a string identifier. (not the contents of the string, just something to identify it)
  • 19. » This is a recommended practice for android applications,» because it allows your application to be translated to different languages more easily!
  • 20. » The orientation attribute (required), which can be set to vertical or horizontal (class: LinearLayout)» The layout_weight attribute (optional, applied to each child control) specifies each child control’s relative importance within the parent linear layout (class: LinearLayout.LayoutParams)» Generic Layout Parameters such as layout_height (required) and layout_width (required) (class: ViewGroup.LayoutParams)» Margin Layout Parameters such as margin_top, margin_left, margin_right and margin_bottom (class: ViewGroup. MarginLayoutParams)» Layout Parameters such as layout_height and layout_width (class: ViewGroup.LayoutParams)
  • 21. » Now, we move on to programming things in the .java file» On the right side, we see the src/…/something.java» This is the main file that we have to edit.
  • 22. This indicates that the project is part of com.example. All code files part of this project should declare this on top.package com.example; All imports required by code goes hereimport android.app.Activity;import android.os.Bundle; Each activity has its own class, some applications may not need this class dependingpublic class MyActivity extends Activity upon implementation{ /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) This function is the entry point. in case the application was { interrupted last time, the super.onCreate(savedInstanceState); previous state is sent as a Bundle setContentView(R.layout.main); to the application } Loads the layout from} main.xml and displays it on the screen
  • 23. » All syntax rules are that of Java!» We implement a java class inherited from activity and override any functions required as per our requirements.» “extends activity” means activity is our base class.» If we want to insert our own functions, they have to be public to be handled by the android engine.
  • 24. » To be able to “listen” to clicks on various objects/views in out UI ˃ Maybe buttons, textviews, radioclicks.. Etc. First,» public class Tabtest01 extends Activity implements OnClickListener { .. } ˃ This allows us to use the OnClickListener interface in the rest of our code.» Then we write a public onclick() function that handles all click events in our activity.» Then we attach the view that we want to be clicked to this function in the oncreate() function
  • 25. TextView clickMe; • First, we need to identify the view using the findViewById() and typecasting it to what we @Override know our result should be. public void onCreate(Bundle savedInstanceState) • clickMe is an object of the exact type of view { that’s going to be returned. super.onCreate(savedInstanceState); • setOnClickListener() attaches the interface to setContentView(R.layout.main); the click listener to the textview with clickMe = (TextView)findViewById(R.id.widget02); id:widget02 clickMe.setOnClickListener(this); }@Override • This method is called whenever a public void onClick(View v) { click is called. The argument “V” if(v==clickMe) { contains details of the view that Toast.makeText(this, “ Clicked! ”,Toast.LENGTH_SHORT).show(); was clicked. clickMe.setBackgroundResource(R.color.green); • Since both functions are part of clickMe.setText("ABCDEFG") the same class, if v==clickMe, then } we know that id:widget02 was } clicked. • Then we can perform manipulations on the required object!
  • 26. » Make a new xml file in res/values/color.xml» Put this inside it:<resources> <color name="white">#ffffffff</color> <color name="black">#ff000000</color> <color name="red">#ffff0000</color> <color name="green">#ff00ff00</color> <color name="blue">#ff0000ff</color></resources>Any number of custom colors that you want can be inserted here andaccessed via R.color.name
  • 27. » Apart from clicking a control/view, in android phones, long pressing on any element performs a secondary function ˃ Serves the purpose of doubleclick which is not recommended.» First in oncreate(), after finding the element, we need to register for context menu.» Then we write two handler functions onCreateContextMenu() and onContextItemSelected() to implement the behaviour we require.
  • 28. TextView clickMe; @Override • First, like we need to identify the view using public void onCreate(Bundle savedInstanceState) the findViewById() and typecasting it and { saving it in a object of same type as the view. super.onCreate(savedInstanceState); setContentView(R.layout.main); • registerForContextMenu() takes a view as clickMe = (TextView)findViewById(R.id.widget02); parameter and registers that view for the clickMe.setOnClickListener(this); longpress to context menu. registerForContextMenu(clickMe); }@Override public void onCreateContextMenu(ContextMenu menu, Viewv,ContextMenuInfo menuInfo) { super.onCreateContextMenu(menu, v, menuInfo); • This method creates the required menu.setHeaderTitle("Context Menu"); context menu and populates its entries. menu.add(0, v.getId(), 0, "Action 1"); • menu.setHeaderTitle() sets the title of menu.add(0, v.getId(), 0, "Action 2"); the context menu. } • And the menu.add() function can set up all the actions possible in that menu.
  • 29. @Override public boolean onContextItemSelected(MenuItem item) { if(item.getTitle()=="Action 1"){ Toast.makeText(this, "function 1 called", Toast.LENGTH_SHORT).show(); } else if(item.getTitle()=="Action 2"){ Toast.makeText(this, "function 1 called", Toast.LENGTH_SHORT).show(); } else {return false;} return true; • This onContextItemSelected() function is called when a } menu item is pressed from the previous function. • The data (as always) comes as argument to the function call.. • using item.getTitle()=="Action 1") we can identify which menu item was pressed and do actions accordingly.. • this function must return true if a valid menu item was processed so that the system can remove the context menu.
  • 30. » A little more flexible than linear layouts.» Allow you to specify views position in relation t each other and their container.» Nested views increase the performance overhead required for application.
  • 31. <?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_height="fill_parent" android:layout_width="fill_parent"> <TextView android:text="RED" android:id="@+id/TextView01" android:layout_height="wrap_content" android:background="#f00" android:gravity="center" android:textColor="#000" android:layout_width="wrap_content" android:padding="25dp"></TextView></RelativeLayout>
  • 32. […]<TextView android:text="ORANGE" android:layout_height="wrap_content" android:background="#ffa500" android:gravity="center" android:textColor="#000" android:id="@+id/TextView02" android:layout_width="wrap_content" android:layout_centerHorizontal="true" android:padding="25dp"></TextView>[…]
  • 33. […]<TextView android:text="YELLOW" android:layout_height="wrap_content" android:background="#ffff00" android:gravity="center" android:textColor="#000" android:id="@+id/TextView03" android:layout_width="wrap_content" android:layout_alignParentRight="true" android:padding="25dp"></TextView>[…]
  • 34. […]<TextView <TextView android:text="GREEN" android:layout_height="wrap_content" android:background="#0f0" android:gravity="center" android:textColor="#000" android:id="@+id/TextView04" android:layout_width="wrap_content" android:layout_toLeftOf="@+id/TextView05" android:padding="25dp" android:layout_centerVertical="true"></TextView>[…]
  • 35. […]<TextView <TextView android:text="BLUE" android:layout_height="wrap_content" android:background="#00f" android:gravity="center" android:textColor="#fff" android:id="@+id/TextView05" android:layout_width="wrap_content" android:layout_centerInParent="true" android:layout_margin="10dp" android:padding="25dp"></TextView>[…]
  • 36. […]<TextView android:text="INDIGO" android:layout_height="wrap_content" android:gravity="center" android:textColor="#fff" android:id="@+id/TextView06" android:layout_width="wrap_content" android:layout_toRightOf="@+id/TextView05" android:background="#4b0082" android:padding="25dp" android:layout_centerVertical="true"></TextView>[…]
  • 37. […]<TextView android:text="VIOLET" android:layout_height="wrap_content" android:background="#ee82ee" android:gravity="center" android:textColor="#000" android:id="@+id/TextView07" android:layout_alignParentBottom="true" android:layout_width="fill_parent" android:padding="25dp"></TextView>[…]