在android中使用允许的字符验证EditText输入

import android.text.Editable;
import android.text.TextWatcher;
import android.widget.EditText;
import java.util.regex.Pattern;

public class MainActivity extends AppCompatActivity {

    private EditText editText;

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

        editText = findViewById(R.id.editText);

        // 添加文本变化监听器
        editText.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {
            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
            }

            @Override
            public void afterTextChanged(Editable s) {
                // 获取输入的文本
                String input = s.toString();

                // 定义允许的字符正则表达式
                String allowedCharacters = "^[a-zA-Z0-9]+$";

                // 验证输入是否符合允许的字符规则
                boolean isValid = Pattern.matches(allowedCharacters, input);

                if (!isValid) {
                    // 输入不符合规则，给出错误提示
                    editText.setError("只允许输入字母和数字");
                }
            }
        });
    }
}