无法动态添加片段

Question

我尝试动态添加片段，但每次我切换到动态添加片段而不是静态添加片段时，应用程序都会停止。

package com.hiro.empty;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentTransaction;

import android.os.Bundle;

public class MainActivity extends AppCompatActivity
{

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

        Fragment fragment = new MyFragment();
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.add(R.id.container, fragment);
        transaction.addToBackStack(null);
        transaction.commit();
    }
}

Logcat 输出：

2019-10-02 15:38:51.056 16022-16022/com.hiro.empty E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.hiro.empty, PID: 16022
    java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
        at android.view.ViewGroup.addViewInner(ViewGroup.java:5106)
        at android.view.ViewGroup.addView(ViewGroup.java:4935)
        at android.view.ViewGroup.addView(ViewGroup.java:4875)
        at android.view.ViewGroup.addView(ViewGroup.java:4848)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:887)
        at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238)
        at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1303)
        at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:439)
        at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManagerImpl.java:2079)
        ...

MyFragment 类

public class MyFragment extends Fragment
{
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
    {
        return inflater.inflate(R.layout.fragment, container);
    }
}

Answer 1

一个关键是inflate 方法中的第三个布尔参数。它会将膨胀的视图附加到父级。要修复错误，您应该将 onCreateView 方法更改为：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
    return inflater.inflate(R.layout.fragment, container, false);
}

避免将 null 作为父级传递以正确设置 LayoutParams。