具有多態性的隨機類android

Question

我正在構建一個算命的 android 應用程序，它使用隨機類從數組中選擇不同的財富，它基於多態性。 我知道我編碼得很好，但我的應用程序甚至無法打開，有什么幫助嗎？ 這是我的代碼：

public class fortuneList {
    Random good = new Random();
    Random bad = new Random();

    public String getGood() {
        String goodFortunes[] = new String[20];
        int sel = 0;
        for (int i = 0; i < 9; i++) {
            sel = good.nextInt();
        }
        goodFortunes[0] = "Adel is awesome";
        goodFortunes[1] = "Adel is cool";
        goodFortunes[2] = "Adel is nice";
        goodFortunes[3] = "Adel is gentle";
        goodFortunes[4] = "Adel is smart";
        goodFortunes[5] = "Adel is rich";
        goodFortunes[6] = "Adel is good";
        goodFortunes[7] = "This is 8";
        goodFortunes[8] = "Change the quotes later";
        return goodFortunes[sel];
    }

    public String getBad() {
        String badFortunes[] = new String[5];
        int sele = 0;
        for (int is = 0; is < 5; is++) {
            sele = bad.nextInt();
        }
        badFortunes[0] = "WTF";
        badFortunes[1] = "Bad 1";
        badFortunes[2] = "Nigga";
        badFortunes[3] = "bish";
        badFortunes[4] = "haha";
        return badFortunes[sele];
    }
}

這是我關於主要活動的代碼：

public class MainActivity extends AppCompatActivity {
    TextView fortuneText;
    Random select = new Random();
    ImageView ball;
    Button button;
    Drawable blue = getResources().getDrawable(R.drawable.blue);
    Drawable red = getResources().getDrawable(R.drawable.red);
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ball = (ImageView) findViewById(R.id.ball);
        button = (Button) findViewById(R.id.button);
        fortuneText = (TextView) findViewById(R.id.fortuneText);

    }

    public void getFortune(View view){
        fortuneList obj = new fortuneList();
        String fortuneType[]={obj.getGood(),obj.getBad()};
        int fortuneSel = 0;
        for(int i =0; i<2;i++){
            fortuneSel = select.nextInt();
        }
        fortuneText.setText(fortuneType[fortuneSel]);
        if (fortuneSel == 0) {
            ball.setImageDrawable(blue);
        }
        if(fortuneSel == 1){
            ball.setImageDrawable(red);
        }
    }
} 

Answer 1

您看到的問題是由於以下幾行：

Drawable blue = getResources().getDrawable(R.drawable.blue);
Drawable red = getResources().getDrawable(R.drawable.red);

在建立上下文之前，您無法實例化可繪制資源。 換句話說，此時您的 Activity 尚未創建，因此您無法調用 getResources()。 您可能在 logcat 中收到NullPointerException 。 嘗試這個：

public class MainActivity extends AppCompatActivity {
    TextView fortuneText;
    Random select = new Random();
    ImageView ball;
    Button button;
    Drawable blue;
    Drawable red;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //Instantiate AFTER your activity.
        blue = getResources().getDrawable(R.drawable.blue);
        red = getResources().getDrawable(R.drawable.red);

        ball = (ImageView) findViewById(R.id.ball);
        button = (Button) findViewById(R.id.button);
        fortuneText = (TextView) findViewById(R.id.fortuneText);

    }

    public void getFortune(View view){
        fortuneList obj = new fortuneList();
        String fortuneType[]={obj.getGood(),obj.getBad()};
        int fortuneSel = 0;
        for(int i =0; i<2;i++){
            fortuneSel = select.nextInt();
        }
        fortuneText.setText(fortuneType[fortuneSel]);
        if (fortuneSel == 0) {
            ball.setImageDrawable(blue);
        }
        if(fortuneSel == 1){
            ball.setImageDrawable(red);
        }
    }
}