Android之MVC——Model通知View去更新（實用）

下面兩段標紅加深的代碼是重點：

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(); } }