从ListView打开一个片段

Question

我有一个Activity，它有一个ListView（元素在数据库中）。我的目标是，如果用户点击列表的元素，它将打开一个新片段。但是我在setOnClickListener部分遇到了一些问题。

这是我的活动：

package com.example.program1;


import android.app.Activity;
import android.content.Context;
import android.database.Cursor;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.Toast;

import java.util.ArrayList;


public class ClassA extends AppCompatActivity {

    DB mydb;
    ListView listView;

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

       listView =(ListView) findViewById(R.id.gradesview);
        mydb = new DB(this);

        final ArrayList<String> theList = new ArrayList<>();
        Cursor data =mydb.getObjectsName();

        if (data.getCount()==0){
            Toast.makeText(class_a.this,"Error",Toast.LENGTH_LONG).show();
        }else {
            while (data.moveToNext()) {
                theList.add(data.getString(0));
                ListAdapter listAdapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, thelist);
                listView.setAdapter(listAdapter);

            }


            listView.setOnItemClickListener(
                    new AdapterView.OnItemClickListener() {
                        @Override
                        public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {

                            Fragment grades = new grades();
                            FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
                            ft.replace(R.id.class_a, grades).commit();

                            Toast.makeText(Class_a.this,"Begin",Toast.LENGTH_LONG).show();

                        }
                    }
            );
        }
    }
}

XML：

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="schemas.android.com/apk/res/android" 
   xmlns:tools="schemas.android.com/tools" 
   android:layout_width="match_parent"
   android:layout_height="match_parent" 
   android:orientation="vertical" 
   android:id="@+id/classa">

    <ListView android:id="@+id/gradesview" 
       android:layout_width="match_parent" 
       android:layout_height="match_parent" />

</LinearLayout>

该程序已构建，但是当我单击除Toast消息之外的其中一个列表项时，没有任何事情发生。

Answer 1

试试吧

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:id="@+id/classa"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <ListView
        android:id="@+id/gradesview"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <FrameLayout
        android:id="@+id/frg"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</LinearLayout> 

Java代码

while (data.moveToNext()) {
            theList.add(data.getString(0));
        }
        ListAdapter listAdapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, thelist);
        listView.setAdapter(listAdapter);


        listView.setOnItemClickListener(
                new AdapterView.OnItemClickListener() {
                    @Override
                    public void onItemClick(AdapterView<?> adapterView, View view, int i, long l) {

                        Fragment grades = new grades();
                        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
                        ft.replace(R.id.frg, grades).commit();
                    }
                }
        );

Answer 2

看到您的xml显示id为“classa”，并且您在片段事务中使用“class_a”作为id。

更改您的片段替换如下：

Fragment grades = new grades();
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.classa, grades).commit();  //<-- change id here