下面两段标红加深的代码是重点：
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
import java.util.Observable;
import java.util.Observer;
// you must implements Observer
public class ObserverExample extends Activity implements Observer { // Button variables for our 4 UI buttons which perform touchdowns and field
// goals for the Home and Away teams.
Button button1;
Button button2;
Button button3;
Button button4; // Score variable for the Score object we'll be using to track and report
// out both teams' scores.
Score score; // TextView variables for our scoreboard display, #2 is Home score, #4 is
// Vistors score.
TextView textView2;
TextView textView4; // Set some constants to make the code more human-readable.
private static final int HOME = 1;
private static final int VISITOR = 2; @Override
public void update(Observable observable, Object data) { // Set the score to the current score each time there's a change.
// Creating a helper method is a nice way to simplify the code here.
setScore();
} // Grabs the score for the Home team and Away team and displays them in
// the correct TextView's of the scoreboard. private void setScore() { textView2.setText(String.valueOf(score.getScore(HOME)));
textView4.setText(String.valueOf(score.getScore(VISITOR)));
} @Override
protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main); // Create a new score object, this will contain all of the logic to
// track and report out both team's scores.
score = new Score(); // Score is an Observable class, therefore, we can use the method
// addObserver to add this Activity as an Observer using it's local
// context. This is the magic sauce that enables instant updates
// whenever the Score changes. When the Score reports a change, the
// update() method runs in this Activity.
score.addObserver(this); // This code ties in our TextView variables to the actual ID's of the UI
// elements themselves.
textView2 = (TextView) findViewById(R.id.textView2);
textView4 = (TextView) findViewById(R.id.textView4); // Ties in the ID of the button to our variable set above.
button1 = (Button) findViewById(R.id.button1); // Creates a new instance of OnClickListener which fires the onClick()
// method upon, well, a click.
button1.setOnClickListener(new OnClickListener() { @Override
public void onClick(View v) { // Update the score by running the touchDown() method for the
// Home team.
score.touchDown(HOME); }
}); // Same idea as above repeated for buttons 2 - 4.
button2 = (Button) findViewById(R.id.button2); button2.setOnClickListener(new OnClickListener() { @Override
public void onClick(View v) { // Update the score by running the fieldGoal() method for the
// Home team.
score.fieldGoal(HOME); }
}); button3 = (Button) findViewById(R.id.button3); button3.setOnClickListener(new OnClickListener() { @Override
public void onClick(View v) { score.touchDown(VISITOR);
}
}); button4 = (Button) findViewById(R.id.button4); button4.setOnClickListener(new OnClickListener() { @Override
public void onClick(View v) { score.fieldGoal(VISITOR);
}
}); } }
import java.util.Observable; // In order to report changes to any interested objects, such as Activities, we
// need to extend the Observable class. This enables other objects to register
// themselves as an Observer by using the addObserver() method.
public class Score extends Observable { // Initialize the score, scores always start at zero.
private int home_score = 0;
private int visitor_score = 0; public Score() { } // Grant 1 point to the team based on the variable fed in HOME == 1
// and VISITOR == 2;
public void fieldGoal(int team)
{ switch (team) {
case 1:
this.home_score = this.home_score + 1;
break; case 2:
this.visitor_score = this.visitor_score + 1;
break;
} triggerObservers(); } // Returns the score of the Home or Visitor teams depending on which
// variable is fed.
public int getScore(int team) { switch (team) {
case 1:
return home_score;
case 2:
return visitor_score;
} return 0;
} // Adds six points to score of the team fed in as a variable, HOME == 1 and
// VISITOR == 2
public void touchDown(int team) { switch (team) {
case 1:
this.home_score = this.home_score + 6;
break; case 2:
this.visitor_score = this.visitor_score + 6;
break;
} triggerObservers();
} // Create a method to update the Observerable's flag to true for changes and
// notify the observers to check for a change. These are also a part of the
// secret sauce that makes Observers and Observables communicate
// predictably.
private void triggerObservers() { setChanged();
notifyObservers();
} }