java - textviewArray[i].setText(stringArray[i]);一片空白

Question

我创建了 TextView 数组并定义了数组中的每个元素，我得到了一个带有 Intent 的字符串数组，但是当我尝试使用通过 for 循环接收字符串数组的元素设置 textview 文本时，它返回 null 这段代码有什么问题？我是java初学者，

public class dizilisActivity extends AppCompatActivity {
TextView player1, player2,player3,player4,player5,player6,player7,player8,player9,player10;
TextView[] players = {player1, player2,player3,player4,player5,player6,player7,player8,player9,player10};
String[] receivedNames;


protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_dizilis);
    player1= (TextView) findViewById(R.id.player1);
    player2= (TextView) findViewById(R.id.player2);
    player3= (TextView) findViewById(R.id.player3);
    player4= (TextView) findViewById(R.id.player4);
    player5= (TextView) findViewById(R.id.player5);
    player6 = (TextView) findViewById(R.id.player6);
    player7 = (TextView) findViewById(R.id.player7);
    player8 = (TextView) findViewById(R.id.player8);
    player9 = (TextView) findViewById(R.id.player9);
    player10 = (TextView) findViewById(R.id.player10);
    Intent intent = getIntent();
    receivedNames = intent.getStringArrayExtra("names");
    for (int i = 0; i<receivedNames.length; ++i)
    players[i].setText(receivedNames[i]);

    }

}

和 logcat

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference at com.easoft.aldimverdim.dizilisActivity.onCreate(dizilisActivity.java:33)

第 33 行是

players[i].setText(receivedNames[i];

Answer 1

TL;DR

1) 改变你的 来自

TextView[] players = {player1, player2,player3,player4,player5,player6,player7,player8,player9,player10}

进入

TextView[] players;

2)移动初始化，所以之后

player10 = (TextView) findViewById(R.id.player10);

添加:

players = new TextView[]{player1, player2, player3, player4, player5, player6, player7, player8, player9, player10};

3) 当receivedNames将为null时，您可以添加额外的条件，例如:

// Check if receivedNames are NOT null
if (receivedNames != null) {
    for (int i = 0; i < receivedNames.length; ++i) {
        // here rest of codes
    }
}

错误解释

1)线路:

TextView player1, player2,player3,player4,player5,player6,player7,player8,player9,player10;

导致声明了 10 个变量。它们都是nulls

2)所以在下一行:

TextView[] players = {player1, player2,player3,player4,player5,player6,player7,player8,player9,player10};

声明新数组并使用 null 值对其进行初始化，以便您的数组内部包含 10 个 null。

[null, null, null, null, null, null, null, null, null, null]

3) 当在 onCreate() 中尝试调用 players[i].setText(...) 时，players[i] 具有 null 值。因此，您对 null 调用 setText。这就是崩溃的原因。

完整的工作代码:

public class MainActivity extends AppCompatActivity {
    TextView player1, player2, player3, player4, player5, player6, player7, player8, player9,
            player10;

    TextView[] players;

    String[] receivedNames;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_dizilis);

        player1 = findViewById(R.id.player1);
        player2 = findViewById(R.id.player2);
        player3 = findViewById(R.id.player3);
        player4 = findViewById(R.id.player4);
        player5 = findViewById(R.id.player5);
        player6 = findViewById(R.id.player6);
        player7 = findViewById(R.id.player7);
        player8 = findViewById(R.id.player8);
        player9 = findViewById(R.id.player9);
        player10 = findViewById(R.id.player10);

        players = new TextView[]{player1, player2, player3, player4, player5, player6, player7,
                player8, player9, player10};

        Intent intent = getIntent();
        receivedNames = intent.getStringArrayExtra("names");

        if (receivedNames != null) {
            for (int i = 0; i < receivedNames.length; ++i) {
                players[i].setText(receivedNames[i]);
            }
        }
    }
}

提示#1

好的做法是从较短或“导致更多问题”中获取索引，因此您可以更改:

i < receivedNames.length

至:

i < players.length

当您从 getStringArrayExtra() 接收到较少数据时 = 没有任何反应(只是空 TextView)。

但是当您尝试分配给不存在的 TextView 或在不存在的数组中定位时=崩溃

提示#2

如果您遇到相同/类似的循环问题，您可以:

• 使用断点(关于在调试模式下构建Android应用程序`) 或
• 添加简单的try-catch block 来检查哪个索引导致问题。例如:

for (int i = 0; i < receivedNames.length; ++i) {
    try {
        players[i].setText(receivedNames[i]);
    } catch (Exception e) {
        System.out.println("Problem with id = " + i);
    }
}