Android之MVC——Model通知View去更新（实用）

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();
    }

}