Fragment问题：java.lang.IllegalStateException

错误提示： 

 Process: com.example.accountapp, PID: 3987
                                                                                                    java.lang.IllegalStateException: Could not execute method for android:onClick
                                                                                                        at androidx.appcompat.app

 Caused by: java.lang.IllegalStateException: commit already called
                                                                                                        at androidx.fragment.app.BackStackRecord.commitInternal(BackStackRecord.java:315)
                                                                                                        at androidx.fragment.app.BackStackRecord.commit(BackStackRecord.java:294) 

这是一个Android应用程序中的严重错误，其中涉及到"java.lang.IllegalStateException"异常。具体来说，错误信息是"Could not execute method for android:onClick"，并且也提到了"commit already called"的问题。这种错误通常出现在Fragment的事务提交上，可能是由于重复调用了commit方法导致的。 

原因：

在Android中，每个 FragmentTransaction 对象只能提交一次。一旦调用了 commit() 方法提交一个事务，该事务就被提交到活动的 FragmentManager 中，之后再次调用 commit() 方法会导致 "Can not perform this action after onSaveInstanceState" 异常或者 "commit already called" 异常。这是因为 commit() 方法已经被调用，再次调用会导致不可预测的行为。

原有代码：

package com.example.accountapp.pages;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.FragmentContainerView;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;

import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

import com.example.accountapp.R;
import com.example.accountapp.fragment.addaccount.AddExchangeFragment;
import com.example.accountapp.fragment.addaccount.AddInFragment;
import com.example.accountapp.fragment.addaccount.AddOutFragment;

public class AddAccount extends AppCompatActivity {
    private int tabIndex = 1; //当前选中的tab页
    private TextView tab1,tab2,tab3,cancelTxt;
    private View divider1,divider2;
    private FragmentContainerView fragmentContainerView;
    private FragmentManager fragmentManager;
    private FragmentTransaction fragmentTransaction;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_add_account);
        initView();
        // 动态加载 Fragment
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();//开启事务
        fragmentTransaction.add(R.id.icon_frag,new AddOutFragment());
        fragmentTransaction.commit();
    }

    // 切换 tab页 点击方法
    public void tabChange(View view) {
        int index = view.getId();
        if(index == R.id.tab1){
            System.out.println("支出");
            divider1.setVisibility(View.INVISIBLE);
            divider2.setVisibility(View.VISIBLE);
            tab1.setBackgroundResource(R.drawable.selec_tab);
            tab3.setBackgroundResource(0);
            tab2.setBackgroundResource(0);
            fragmentTransaction.replace(R.id.icon_frag,new AddOutFragment());
        }else if(index == R.id.tab2){
            System.out.println("收入");
            divider1.setVisibility(View.INVISIBLE);
            divider2.setVisibility(View.INVISIBLE);
            tab2.setBackgroundResource(R.drawable.selec_tab);
            tab1.setBackgroundResource(0);
            tab3.setBackgroundResource(0);
            FragmentManager fragmentManager = getSupportFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();//开启事务
            fragmentTransaction.replace(R.id.icon_frag,new AddInFragment());
        }else{
            System.out.println("转账");
            divider1.setVisibility(View.VISIBLE);
            divider2.setVisibility(View.INVISIBLE);
            tab3.setBackgroundResource(R.drawable.selec_tab);
            tab1.setBackgroundResource(0);
            tab2.setBackgroundResource(0);
            fragmentTransaction.replace(R.id.icon_frag,new AddExchangeFragment());
        }
        fragmentTransaction.commit();
    }
}

修改过后:

每次创建新的 FragmentTransaction 对象

package com.example.accountapp.pages;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.FragmentContainerView;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;

import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

import com.example.accountapp.R;
import com.example.accountapp.fragment.addaccount.AddExchangeFragment;
import com.example.accountapp.fragment.addaccount.AddInFragment;
import com.example.accountapp.fragment.addaccount.AddOutFragment;

public class AddAccount extends AppCompatActivity {
    private int tabIndex = 1; //当前选中的tab页
    private TextView tab1,tab2,tab3,cancelTxt;
    private View divider1,divider2;
    private FragmentContainerView fragmentContainerView;
    private FragmentManager fragmentManager;
    private FragmentTransaction fragmentTransaction;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_add_account);
        initView();
        // 动态加载 Fragment
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();//开启事务
        fragmentTransaction.add(R.id.icon_frag,new AddOutFragment());
        fragmentTransaction.commit();
    }
 // 切换 tab页 点击方法
    public void tabChange(View view) {
        int index = view.getId();
        if(index == R.id.tab1){
            System.out.println("支出");
            divider1.setVisibility(View.INVISIBLE);
            divider2.setVisibility(View.VISIBLE);
            tab1.setBackgroundResource(R.drawable.selec_tab);
            tab3.setBackgroundResource(0);
            tab2.setBackgroundResource(0);
            FragmentManager fragmentManager = getSupportFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();//开启事务
            fragmentTransaction.replace(R.id.icon_frag,new AddOutFragment());
            fragmentTransaction.commit();
        }else if(index == R.id.tab2){
            System.out.println("收入");
            divider1.setVisibility(View.INVISIBLE);
            divider2.setVisibility(View.INVISIBLE);
            tab2.setBackgroundResource(R.drawable.selec_tab);
            tab1.setBackgroundResource(0);
            tab3.setBackgroundResource(0);
            FragmentManager fragmentManager = getSupportFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();//开启事务
            fragmentTransaction.replace(R.id.icon_frag,new AddInFragment());
            fragmentTransaction.commit();
        }else{
            System.out.println("转账");
            divider1.setVisibility(View.VISIBLE);
            divider2.setVisibility(View.INVISIBLE);
            tab3.setBackgroundResource(R.drawable.selec_tab);
            tab1.setBackgroundResource(0);
            tab2.setBackgroundResource(0);
            FragmentManager fragmentManager = getSupportFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();//开启事务
            fragmentTransaction.replace(R.id.icon_frag,new AddExchangeFragment());
            fragmentTransaction.commit();
        }
    }
}