图像查看器的片段 (Android)

Question

我正在尝试创建一个仅在单击时显示图像的简单片段。我遇到了很多错误，包括“对于 ExampleFragment 类型的 findViewbyId(int) 方法未定义”、“Inflater 无法解析”和“imageview_main 无法解析或不是字段”。 imageview_main 是我创建的布局，imageView1 是该布局中包含的图像。这是片段代码：

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);
        }

    });

}

Answer 1

findViewById 是 Activity 类中的一个方法。为避免传递整个活动的实例，请使用 Wea​​kRefence（请参阅 http://developer.android.com/reference/java/lang/ref/WeakReference.html） 例如

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);
}

Answer 2

我在您的代码中添加了以下修改；

1) 从支持库导入 Fragment（如果在早期版本的 android 上运行很重要）；

2）Insted of Inflater 我使用收到的inflater作为方法参数；

3) 我创建了一个可以在这个片段中使用的方法 findViewById；

4) 我在 onActivityCreated 方法中移动了一些初始化代码； Here

您可以找到有关该方法的更多信息；

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);
        }

    });

}