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[英]how to pass a value from an activity class to a java class in android?
[英]How do I pass arrays from a java android activity class to a normal java class?
我是java的新手,在類之間傳遞數組時遇到問題。 我想將從主活動收集的數據傳遞給另一個正在進行計算的類。 當我嘗試將數組值打印到我的計算類中的調試日志時,我收到錯誤“java.lang.NullPointerException:嘗試從空數組中讀取”
這是我的計算課:
package com.example.pokerholdemcalculator;
import android.util.Log;
public class CardHandling {
private int[] usedCards;
private MainActivity ma;
CardHandling() {
usedCards = new int[13];
ma = new MainActivity();
usedCards = ma.getPlayerCardContents();
}
public void printC () {
for (int i = 0; i < 13; i++) {
String card = Integer.toString(usedCards[i]);
Log.d("CARDS", card);
}
}
}
我的MainActivity類:
package com.example.pokerholdemcalculator;
import android.graphics.PorterDuff;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ImageButton;
import android.widget.ViewFlipper;
public class MainActivity extends AppCompatActivity {
private ViewFlipper viewFlipper;
private boolean[] playerCardFlag;
private ImageButton[] playerCard;
private int[] playerCardContents;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
playerCard = new ImageButton[13];
playerCardFlag = new boolean[13];
playerCardContents = new int[13];
}
public void testing (View v) {
printArr();
}
public void printArr() {
CardHandling ch = new CardHandling();
ch.printC();
}
public int[] getPlayerCardContents() {
return playerCardContents;
}
這是來自控制台的錯誤消息:
Caused by: java.lang.NullPointerException: Attempt to read from null array
at com.example.pokerholdemcalculator.MainActivity.getPlayerCardContents(MainActivity.java:70)
at com.example.pokerholdemcalculator.CardHandling.<init>(CardHandling.java:12)
at com.example.pokerholdemcalculator.MainActivity.printArr(MainActivity.java:64)
at com.example.pokerholdemcalculator.MainActivity.testing(MainActivity.java:60)
我嘗試過以不同方式初始化但無法解決錯誤。
這里的主要問題是您的活動不能像這樣被引用:
ma = new MainActivity();
usedCards = ma.getPlayerCardContents();
想要做的就是在主要活動上啟動課程
CardHandling ch = new CardHandling();
ch.usedCard = getPlayerCardContents();
MainActivity擴展了AppCompatActivity,這意味着您的活動不是普通對象
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