Basic Android

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Android Basics

Basics

  • src folder containing all the source
  • res folder containing all the resources

folder hierarchy explained http://developer.android.com/tools/projects/index.html

First app demo http://developer.android.com/training/basics/firstapp/running-app.html

App lifecycle http://developer.android.com/guide/components/activities.html

activity_lifecycle.png

Resources

No DPI or PPI Andoid uses dp density independent pixels or sp scale interdependent pixels http://developer.android.com/guide/topics/resources/more-resources.html#Dimension

also see supporting multiple screens http://developer.android.com/guide/practices/screens_support.html

Activities

Activity life cycle http://developer.android.com/guide/topics/fundamentals/activities.html#Lifecycle

Get an instance of an object from the R class

/** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        //Get the Button and the TextView from the Resource class
        Button btn = (Button)this.findViewById(R.id.button1); //needs import android.widget.Button;

        //Final in java can only be initialized once this is necessary to for use in inner method
        final TextView tv = (TextView)this.findViewById(R.id.textView1);  //needs import android.widget.TextView;
        String s = "hello";
        tv.setText(s);
    }
notice the cast to the type also notice that the TextView is marked as final 
this is so that we can use it in an inner method

handle a click event

btn.setOnClickListener(new View.OnClickListener() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				tv.setText(d.About());
			}
		});

We can also do this without the inner method by declaring a click method in the class

public void buttonPressMe_OnCLick(View v)
    {
        TextView tv = (TextView)this.findViewById(R.id.textView2);
        tv.setText("Hello From Button!!");
    }

Then we can set the click handler in the layout xml in out case acivity_main.xml

<Button
        android:text="Press Me"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textView"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_marginLeft="13dp"
        android:layout_marginStart="13dp"
        android:layout_marginTop="24dp"
        android:id="@+id/buttonPressMe"
        android:onClick="buttonPressMe_OnCLick (MainActivity)" />

Events

Lots more good reading http://developer.android.com/guide/topics/fundamentals.html


AVD

Dog Class in java

public class Dog {
    public String Name; //Java uses capital S String
    public int Weight;
    public String BarkSound;

    //Constructor
    public Dog()
    {
        this.Name = "fido";
        this.Weight = 1;
        this.BarkSound = "woof";
    }

    public void Eat()
    {
        this.Weight++;
    }
    public void Poop()
    {
        this.Weight--;
    }

    public String About()
    {
        //Java string.format is similar to c# but used %s for string substitution
        return String.format("Hello my name is %s. I weigh %s lbs",
                this.Name, this.Weight);
    }
}

In Class Demo

AndroidStudioConfigure.png

  • Select Android SDK Manager

AndroidStudioSDKManager.png

  • Make sure you have a current SDK for this Demo we will use 24

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  • Go back to the main menu and select New Project

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  • Name the Project OOPDog and select Next

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  • Select a Minimum SDK for this demo we will use API15 : IceCreamSandwich

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  • Select Blank Activity for the Project template

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  • The defaults are fine for the activity name select next

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  • After a minute or so you can open the Project window if it isn't already open Att-1 or View/Tool Windows/Project

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  • Add Dog class

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  • Name the class Dog

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  • Here is the c# dog class we have been using we need to change it a bit

Android Studio CSharpDog Code

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