Fragment for Image Viewer (Android)

问题:

I'm trying to create a simple fragment that merely displays an image when clicked. I'm getting numerous errors inlcuding "the method findViewbyId(int) is undefined for the type ExampleFragment", "Inflater cannot be resolved", and "imageview_main cannot be resolved or is not a field." imageview_main is a layout I have created, imageView1 is an image contained in that layout. Here is the fragment code:

package com.firstproject.simplemenu;
import android.app.Activity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup; 
import android.view.View.OnClickListener;
import android.widget.Button;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;

import android.app.Fragment;
import android.widget.ImageView;

public class ExampleFragment extends Fragment {

Button button;
ImageView image;


public ExampleFragment() {

}

public static ExampleFragment newInstance() {
    return new ExampleFragment();
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
    ImageView imageview = (ImageView)findViewById(R.id.imageView1);
    return Inflater.inflate(R.layout.iamgeview_main, container, false);
    }

public void addListenerOnButton() {


    button = (Button) findViewById(R.id.btnChangeImage);
    button.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View arg0) {
            image.setImageResource(R.drawable.eagle);
        }

    });

}

回答1:

findViewById is a method in the class Activity. To avoid passing an instance of the entire activity use a WeakRefence (see http://developer.android.com/reference/java/lang/ref/WeakReference.html) for example

private WeakReference<MainActivity> activity;

public ExampleFragment(MainActivity mainActivity) {
   activity = new WeakReference<MainActivity>(mainActivity);
} 

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
    Bundle savedInstanceState) {
    ImageView imageview = (ImageView)activity.findViewById(R.id.imageView1);
    return Inflater.inflate(R.layout.iamgeview_main, container, false);
}

回答2:

I added the following modifications to your code ;

1) Import Fragment from support library(important if running on early versions of android);

2) Insted of Inflater I used the inflater received as method param;

3) I created a method findViewById that can be used in this fragment;

4) I moved some of the initialisation code in the method onActivityCreated ; Here

you cand find more about that method ;

package com.example.gctest;
import android.app.Activity;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup; 
import android.view.View.OnClickListener;
import android.webkit.WebView.FindListener;
import android.widget.Button;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;

import android.widget.ImageView;

public class ExampleFragment extends Fragment {

Button button;
ImageView image;


public ExampleFragment() {

}

public static ExampleFragment newInstance() {
    return new ExampleFragment();
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {

        //ImageView imageview = (ImageView)findViewById(R.id.imageView1); this will raise NullPointerException because the parent view has not been created. Is is created with this method;
        return inflater.inflate(R.layout.iamgeview_main, container, false); //just return the  view ;
    }

@Override
    public void onActivityCreated(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        //here you can initialise your variables,listeners,e.t.c ;
        super.onActivityCreated(savedInstanceState);

        ImageView imageview = (ImageView)findViewById(R.id.imageView1);
        addListenerOnButton();
    }

/**
 * You can use this method in order to access the child views of the fragment parent view;
 * @param id
 * @return
 */
protected View findViewById(int id)
{
    return getView().findViewById(id);
}

public void addListenerOnButton() {


    button = (Button) findViewById(R.id.btnChangeImage);
    button.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View arg0) {
            image.setImageResource(R.drawable.eagle);
        }

    });

}