通过程序操作除 main_xml 之外的 xml
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【中文标题】通过程序操作除 main_xml 之外的 xml【英文标题】：manipulating xml other then main_xml through program 【发布时间】：2019-01-14 06:42:33 【问题描述】：我正在创建一个图像下载应用程序，它获取图像 URL、下载图像并将它们显示在列表视图中。为此，我正在通过程序操作 xml。问题是我如何通过程序操作不是我的主要 xml 文件的 xml 文件。
ImageDownloader 类：
public class ImageDownloader extends AsyncTask<String, Void, Bitmap>
private ImageView imageView;
private ProgressBar progressBar;
public ImageDownloader(ImageView imageView, ProgressBar progressBar)
this.imageView = imageView;
this.progressBar = progressBar;
@Override
protected void onPreExecute()
super.onPreExecute();
imageView.setVisibility(View.GONE);
progressBar.setVisibility(View.VISIBLE);
@Override
protected Bitmap doInBackground(String... params)
try
URL url = new URL(params[0]);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.connect();
if(connection.getContentType().contains("image"))
InputStream inputStream = connection.getInputStream();
return BitmapFactory.decodeStream(inputStream);
catch(Exception e)
e.printStackTrace();
return null;
@Override
protected void onPostExecute(Bitmap bitmap)
super.onPostExecute(bitmap);
try
imageView.setImageBitmap(bitmap);
progressBar.setVisibility(View.GONE);
imageView.setVisibility(View.VISIBLE);
catch (Exception e)
e.printStackTrace();
ImageUI 类：
public class ImageUI
private Context context;
private ArrayList<String> urls;
private ImageView imageView;
private ProgressBar progressBar;
private RelativeLayout relativeLayout;
public ImageUI(Context context, ArrayList<String> urls, RelativeLayout relativeLayout)
this.context = context;
this.urls = urls;
this.relativeLayout = relativeLayout;
private void buildUI()
imageView = new ImageView(context);
imageView.setVisibility(View.GONE);
progressBar = new ProgressBar(context);
progressBar.setIndeterminate(true);
progressBar.setVisibility(View.GONE);
relativeLayout = new RelativeLayout(context);
relativeLayout.setGravity(1);
relativeLayout.addView(imageView);
relativeLayout.addView(progressBar);
public RelativeLayout downloadImages()
int i = 0;
while(i < urls.size())
buildUI();
ImageDownloader imageDownloader = new ImageDownloader(imageView, progressBar);
imageDownloader.execute(urls.get(i));
imageDownloader = null;
i++;
return relativeLayout;
return null;
RowItem 类：
public class RowItem
private RelativeLayout relativeLayout;
public RowItem(RelativeLayout relativeLayout)
this.relativeLayout = relativeLayout;
public RelativeLayout getRelativeLayout()
return relativeLayout;
public void setRelativeLayout(RelativeLayout relativeLayout)
this.relativeLayout = relativeLayout;
CustomListViewAdapter 类：
public class CustomListViewAdapter extends ArrayAdapter<RowItem>
Context context;
public CustomListViewAdapter(Context context, int resourseID, List<RowItem> items)
super(context, resourseID, items);
this.context = context;
private class ViewHolder
RelativeLayout relativeLayout;
public View getView(int position, View convertView, ViewGroup parent)
ViewHolder holder = null;
RowItem rowItem = getItem(position);
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
if(convertView == null)
convertView = inflater.inflate(R.layout.list_item, null);
holder = new ViewHolder();
holder.relativeLayout = (RelativeLayout) convertView.findViewById(R.id.relativeLayout);
convertView.setTag(holder);
else
holder = (ViewHolder) convertView.getTag();
return convertView;
MainActivity 类：
public class MainActivity extends AppCompatActivity
ArrayList<RelativeLayout> images;
ArrayList<String> urls = new ArrayList<>();
RelativeLayout relativeLayout = (RelativeLayout) findViewById(R.id.relativeLayout);
List<RowItem> rowItems;
ListView listView;
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
addUrls();
images = new ArrayList<>();
for (int i = 0; i < urls.size(); i++)
ImageUI imageUI = new ImageUI(this, urls, relativeLayout);
images.add(imageUI.downloadImages());
rowItems = new ArrayList<>();
for (int i = 0; i < images.size(); i++)
RowItem item = new RowItem(images.get(i));
rowItems.add(item);
listView = (ListView) findViewById(R.id.listView);
CustomListViewAdapter adapter = new CustomListViewAdapter(this,
R.layout.list_item, rowItems);
listView.setAdapter(adapter);
public void addUrls()
urls.add("https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcTXEZRoYOhIJxL5foNz_NlatDlgYStzZgVIiKuo6vtRtz2wY-8b4Q");
urls.add("https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSFL3WYbqNOX-dwjtT1LroBlY5W-3YuwSIuCMRaLpnjMXbVPEJy");
urls.add("https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQiwgrJeAJN-7lcy92N51uP7XzccK_p-fTSJNCXPLPSVih8wqPf");
urls.add("https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcT19dYLCEZlMRqojedJB-05jTrflD74nasvkXs-SdVeyM2BEpCSFA");
urls.add("http://wallpaperswide.com/download/high_tech_earth-wallpaper-2880x1800.jpg");
urls.add("https://www.gettyimages.ca/gi-resources/images/Homepage/Hero/UK/CMS_Creative_164657191_Kingfisher.jpg");
urls.add("https://images.unsplash.com/photo-1418489098061-ce87b5dc3aee?ixlib=rb-0.3.5&ixid=eyJhcHBfaWQiOjEyMDd9&s=2f033882f3c25404e3f904fbfe2351be&w=1000&q=80");
urls.add("https://techcrunch.com/wp-content/uploads/2018/03/gettyimages-705351545.jpg?w=730&crop=1");
此代码给出错误：
08-07 13:29:31.865 17741-17741/com.example.danishrizvi.test3 E/MemoryLeakMonitorManager: MemoryLeakMonitor.jar is not exist!
08-07 13:29:31.916 17741-17741/? E/androidRuntime: FATAL EXCEPTION: main
Process: com.example.danishrizvi.test3, PID: 17741
java.lang.RuntimeException: Unable to instantiate activity ComponentInfocom.example.danishrizvi.test3/com.example.danishrizvi.test3.MainActivity: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3092)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3302)
at android.app.ActivityThread.-wrap12(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1891)
at android.os.Handler.dispatchMessage(Handler.java:108)
at android.os.Looper.loop(Looper.java:166)
at android.app.ActivityThread.main(ActivityThread.java:7425)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference
at android.support.v7.app.AppCompatDelegateImplBase.<init>(AppCompatDelegateImplBase.java:120)
at android.support.v7.app.AppCompatDelegateImplV9.<init>(AppCompatDelegateImplV9.java:155)
at android.support.v7.app.AppCompatDelegateImplV11.<init>(AppCompatDelegateImplV11.java:31)
at android.support.v7.app.AppCompatDelegateImplV14.<init>(AppCompatDelegateImplV14.java:55)
at android.support.v7.app.AppCompatDelegateImplV23.<init>(AppCompatDelegateImplV23.java:33)
at android.support.v7.app.AppCompatDelegateImplN.<init>(AppCompatDelegateImplN.java:33)
at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:201)
at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:185)
at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:519)
at android.support.v7.app.AppCompatActivity.findViewById(AppCompatActivity.java:190)
at com.example.danishrizvi.test3.MainActivity.<init>(MainActivity.java:18)
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1178)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3082)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3302)
at android.app.ActivityThread.-wrap12(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1891)
at android.os.Handler.dispatchMessage(Handler.java:108)
at android.os.Looper.loop(Looper.java:166)
at android.app.ActivityThread.main(ActivityThread.java:7425)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)
在这一行：
RelativeLayout relativeLayout = (RelativeLayout) findViewById(R.id.relativeLayout);
【问题讨论】：
【参考方案1】：移动
RelativeLayout relativeLayout = (RelativeLayout) findViewById(R.id.relativeLayout);
里面
onCreate:
@Override
protected void onCreate(Bundle savedInstanceState)
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
RelativeLayout relativeLayout = (RelativeLayout) findViewById(R.id.relativeLayout)
addUrls();
// the rest of your code
您需要先调用setContentView，然后才能使用findViewById，或者换句话说：您需要先扩充View，然后才能在其中搜索子视图。
这是因为，在内部，findViewById 确实在做getWindow().findViewById(id)
【讨论】：
这消除了错误，应用程序运行成功，但应用程序是空白的，什么都不显示？ @SyedDanish 这是因为您没有在 CustomListViewAdapter 的 getView 方法中对 RecyclerView 项目设置任何内容。您需要沿 holder.image.setImageBitmap(image) 行添加一些内容，并对 R.layout.list_item 中的每个视图执行相同操作。您将在this answer 中找到一个工作示例。我希望它有所帮助；）以上是关于通过程序操作除 main_xml 之外的 xml的主要内容，如果未能解决你的问题，请参考以下文章
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