Question

我的问题是我有一个创建arraylist的方法。我可以根据需要将其传递给其他方法。但是，当用户点击＆＃34;计算＆＃34;时，我想调用方法calculate。使用以前创建的数组列表的按钮，但我不知道该怎么做。

我最接近的是将我的arraylist声明为全局变量，但我知道全局变量通常都很糟糕，即便如此，我在代码Cannot resolve symbol 'al'的最后一行得到lookUpMethod(al, lookUpString);。

我不确定我做错了什么或最好的方法是什么。

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ArrayList<String []> al = new ArrayList<>(); //tried global variable
        exampleArrayListofArray (al);

    }

    public void exampleArrayListofArray (List<String []> al) {
        //ArrayList<String []> al = new ArrayList<>();  //original array list declaration
        al.add(new String[] {"AB","YZ","12"});
        al.add(new String[] {"CD","WX", "34"});
        al.add(new String[] {"EF","UV", "56"});
        al.add(new String[] {"GH","ST", "78"});
        al.add(new String[]{"IJ", "QR", "91"});
        al.add(new String[]{"KL", "OP", "10"});
        displayArrayListofArray(al);
    }

    public void displayArrayListofArray(List<String[]> al) {

        for (String [] row : al)
            for (int column = 0; column <= 2 ; column ++){
                System.out.println("Value at Index Row " + al.indexOf(row) +
                        " Column " + column + " is " + (row)[column]);
            }
        EditText userField = (EditText) findViewById(R.id.user_field);
        String lookUpString = userField.getText().toString();
        lookUpMethod(al, lookUpString);

    }

    public void lookUpMethod(List<String[]> al, String lookUpString) {
        boolean isStringFound = false;
        for (String[] row : al) {
            for (int column = 0; column <= 2; column++) {
                if (al.get(al.indexOf(row))[column].equals(lookUpString)) {
                    System.out.println("Index of '" + lookUpString + "': " + al.indexOf(row) + column);
                    isStringFound = true;
                }
            }
        }
        if (!isStringFound) {
            System.out.println("Search string '" + lookUpString + "' does not exist.");
        }
    }

    public void calculate(View view){
        EditText userField = (EditText) findViewById(R.id.user_field);
        String lookUpString = userField.getText().toString();
        System.out.println("user input : " + lookUpString);

        lookUpMethod(al, lookUpString);

    }
}

Answer 1

全局变量应该在onCreate之外定义，我认为它通常不好，你可以试试这段代码：

public class MainActivity extends AppCompatActivity {

    private ArrayList<String []> al; //global variable in class

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        al = new ArrayList<>();
        exampleArrayListofArray (al);

    }

    public void exampleArrayListofArray (List<String []> al) {
        //ArrayList<String []> al = new ArrayList<>();  //original array list declaration
        al.add(new String[] {"AB","YZ","12"});
        al.add(new String[] {"CD","WX", "34"});
        al.add(new String[] {"EF","UV", "56"});
        al.add(new String[] {"GH","ST", "78"});
        al.add(new String[]{"IJ", "QR", "91"});
        al.add(new String[]{"KL", "OP", "10"});
        displayArrayListofArray(al);
    }

    public void displayArrayListofArray(List<String[]> al) {

        for (String [] row : al)
            for (int column = 0; column <= 2 ; column ++){
                System.out.println("Value at Index Row " + al.indexOf(row) +
                        " Column " + column + " is " + (row)[column]);
            }
        EditText userField = (EditText) findViewById(R.id.user_field);
        String lookUpString = userField.getText().toString();
        lookUpMethod(al, lookUpString);

    }

    public void lookUpMethod(List<String[]> al, String lookUpString) {
        boolean isStringFound = false;
        for (String[] row : al) {
            for (int column = 0; column <= 2; column++) {
                if (al.get(al.indexOf(row))[column].equals(lookUpString)) {
                    System.out.println("Index of '" + lookUpString + "': " + al.indexOf(row) + column);
                    isStringFound = true;
                }
            }
        }
        if (!isStringFound) {
            System.out.println("Search string '" + lookUpString + "' does not exist.");
        }
    }

    public void calculate(View view){
        EditText userField = (EditText) findViewById(R.id.user_field);
        String lookUpString = userField.getText().toString();
        System.out.println("user input : " + lookUpString);

        lookUpMethod(al, lookUpString);

    }
}

Answer 2

在ArrayList<String []> al = new ArrayList<>();函数之外声明onCreate。

我真的不知道你是如何遇到这种问题的，因为现在所有的功能都会看到你的变量。作为清理，您可以在调用函数时删除变量al，因为不再需要它，因为每个函数现在都可以看到它。如果我没弄错的话，你的最终代码如下：

public class MainActivity extends AppCompatActivity {

    ArrayList<String []> al = new ArrayList<>(); //declare it here


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        exampleArrayListofArray ();

    }

    public void exampleArrayListofArray () {

        al.add(new String[] {"AB","YZ","12"});
        al.add(new String[] {"CD","WX", "34"});
        al.add(new String[] {"EF","UV", "56"});
        al.add(new String[] {"GH","ST", "78"});
        al.add(new String[]{"IJ", "QR", "91"});
        al.add(new String[]{"KL", "OP", "10"});
        displayArrayListofArray();
    }

    public void displayArrayListofArray() {

        for (String [] row : al)
            for (int column = 0; column <= 2 ; column ++){
                System.out.println("Value at Index Row " + al.indexOf(row) +
                        " Column " + column + " is " + (row)[column]);
            }
        EditText userField = (EditText) findViewById(R.id.user_field);
        String lookUpString = userField.getText().toString();
        lookUpMethod(lookUpString);

    }

    public void lookUpMethod(String lookUpString) {
        boolean isStringFound = false;
        for (String[] row : al) {
            for (int column = 0; column <= 2; column++) {
                if (al.get(al.indexOf(row))[column].equals(lookUpString)) {
                    System.out.println("Index of '" + lookUpString + "': " + al.indexOf(row) + column);
                    isStringFound = true;
                }
            }
        }
        if (!isStringFound) {
            System.out.println("Search string '" + lookUpString + "' does not exist.");
        }
    }

    public void calculate(View view){
        EditText userField = (EditText) findViewById(R.id.user_field);
        String lookUpString = userField.getText().toString();
        System.out.println("user input : " + lookUpString);

        lookUpMethod(lookUpString);

    }
}

请注意我是如何删除＆＃34; al＆＃34;在函数调用和函数参数中。将al作为通过函数传递的局部变量的问题是，当您点击calculate按钮时，calculate函数看不到al，除非它{＆＃39} ;一个全局变量。

去尝试修改后的代码。

Answer 3

您需要将函数外部的arrayList解析为全局变量。

ArrayList al = new ArrayList＆lt;＆gt;（）;

Answer 4

范围：局部变量仅在声明它们的方法或块中可见，而实例变量可以被类中的所有方法看到。声明它们的位置：局部变量在方法或块内声明，而实例变量在类中但在方法外部声明。

你需要声明

ArrayList<String []> al = new ArrayList<>();

在onCreate函数之外。

如何将arraylist从onClick传递给方法

4 个答案: