从另一片段的其他视图控制片段的视图

Question

我正在写一个使用片段的简单示例。在主体活动中，有两个片段。第一个片段有一些文本视图，第二个片段有一些按钮。当用户点击textview时，文本打开按钮将被更改。

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal"
    tools:context=".MainActivity" android:background="@drawable/ic_launcher_background">

    <fragment
        android:id="@+id/MenuFrag"
        android:name="www.myapplication.MenuFrag"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1" />

    <fragment
        android:id="@+id/ContentFrag"
        android:name="www.myapplication.ContentFrag"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="3" />
</LinearLayout>

mainactivity.java

package www.application;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity implements MenuFrag.IFragmentClickListener{

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

    @Override
    public void onMenuItemClick(int position) {
        ContentFrag content = (ContentFrag) getSupportFragmentManager().findFragmentById(R.id.ContentFrag);
        if(content!=null)
            content.updateContent(position);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorPrimaryDark"
    tools:context=".MenuFrag">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <TextView
            android:id="@+id/tv1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:fontFamily="sans-serif-smallcaps"
            android:text="TextView 1"
            android:textSize="20sp"
            android:typeface="serif" />

        <TextView
            android:id="@+id/tv2"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:fontFamily="sans-serif-smallcaps"
            android:text="TextView 2"
            android:textSize="20sp"
            android:typeface="serif" />

        <TextView
            android:id="@+id/tv3"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:fontFamily="sans-serif-smallcaps"
            android:text="TextView 3"
            android:textSize="20sp"
            android:typeface="serif" />

        <TextView
            android:id="@+id/tv4"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:fontFamily="sans-serif-smallcaps"
            android:text="TextView 4"
            android:textSize="20sp"
            android:typeface="serif" />

        <TextView
            android:id="@+id/tv5"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:fontFamily="sans-serif-smallcaps"
            android:text="TextView 5"
            android:textSize="20sp"
            android:typeface="serif" />
    </LinearLayout>

</FrameLayout>

package www.application;

import android.content.Context;
import android.os.Bundle;
import android.support.v4.app.ListFragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ListView;
import android.widget.TextView;

public class MenuFrag extends ListFragment {
    IFragmentClickListener itemfragment;
    TextView tv1;

    private View.OnClickListener onclick = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
                 itemfragment.onMenuItemClick(1);
        }
    };

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.menu_frag, container, false);
        tv1= view.findViewById(R.id.tv1);
        tv1.setOnClickListener(onclick);
        return view;
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        try {
            itemfragment = (IFragmentClickListener) context;
        }catch(ClassCastException e){e.printStackTrace();}
    }

    @Override
    public void onListItemClick(ListView l, View v, int position, long id) {
        itemfragment.onMenuItemClick(position);
    }

    public interface IFragmentClickListener{
        public void onMenuItemClick(int position);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorPrimary"
    tools:context=".ContentFrag">
    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/btmessage"/>
    </ScrollView>

</FrameLayout>

contentFrag.java

package www.application;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;

public class ContentFrag extends Fragment {

    Button btmessage;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.content_frag, container, false);
        btmessage = v.findViewById(R.id.btmessage);
        return v;
    }

    public void updateContent(int position){
        btmessage.setText("You clicked !");
    }
}

我没有编写控制按钮的操作，只是生成onclick事件。但是，我弄错了。请帮助我修复错误，并继续完成我的任务。

Answer 1

问题在于MenuFrag片段初始化TextView的方式。
ietv1=getActivity().findViewById(r.id.tv1)；

相反，我建议将其移动到onCreateView()。像这样：

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.menu_frag, container, false);
    tv1 = view.findViewById(R.id.tv1);
    tv1.setOnClickListener(onclick);
    return view;
} 

当您调用getActivity().findViewByID时，它会在Activity的布局中搜索找不到的TextView id。