android fragment 无法在模拟器中打开

Question

首先，我是新的 android 和英语 :) 对此感到抱歉。我对 fragment 管理器有疑问。我阅读了一些在主要 Activity 中使用 fragment 的代码。但是它不能在模拟器中运行，您也可以在下面查看代码。我认为关于“import android.support.v4.app.FragmentManager;”的问题线。我不知道也许我必须像那样使用它“import android.app.FragmenManager”我希望你能理解我的句子并帮助我。谢谢。

   package com.example.ilk.fragmenttransactions;

import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Toast;



public class MainActivity extends FragmentActivity {

    FragmentManager fm;

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

    public void addA(View v){
        FragmentA f1 = new FragmentA();
        FragmentTransaction transaction = fm.beginTransaction();
        transaction.add(R.id.fragment_container, f1, "A");
        transaction.commit();
    }

    public void removeA(View v){
        FragmentA f1 = (FragmentA)fm.findFragmentByTag("A");
        FragmentTransaction transaction = fm.beginTransaction();
        if(f1 != null){
            transaction.remove(f1);
            transaction.commit();
        }
        else{
            Toast.makeText(this, "There is no A! you cannot delete it", Toast.LENGTH_LONG).show();
        }
    }

    public void addB(View v){
        FragmentB f2 = new FragmentB();
        FragmentTransaction transaction = fm.beginTransaction();
        transaction.add(R.id.fragment_container, f2, "B");
        transaction.commit();
    }

    public void removeB(View v){
        FragmentB f2 = (FragmentB)fm.findFragmentByTag("B");
        FragmentTransaction transaction = fm.beginTransaction();
        if(f2 != null){
            transaction.remove(f2);
            transaction.commit();
        }
        else{
            Toast.makeText(this, " There is no B! you cannot delete it ",Toast.LENGTH_SHORT).show();
        }
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

Answer 1

使用import android.support.v4.app.FragmentManager。

fragment 未加载，因为您在应用初始化时未进行任何交易:

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

我认为您正在尝试通过单击布局的元素来加载 fragment

android:onClick 属性

例如:

<Button
    android:id="@+id/myButton"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:onClick="addA" />

执行这个方法的:

  public void addA(View v){
        FragmentA f1 = new FragmentA();
        FragmentTransaction transaction = fm.beginTransaction();
        transaction.add(R.id.fragment_container, f1, "A");
        transaction.commit();
    }