Question

我在FragmentPagerAdapter中有一堆片段，每个片段旁边有一个ImageView。如果我快速刷卡，则会出现此错误：

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"/>
<script src="jquery.js"></script>
<script type="text/javascript">

function dataRet (d){
console.log(d);
}
function ajaxreq(){
debugger
 $.ajax({

url: *some link*
      error: function(jqxhr) {
          alert(jqxhr.responseText); // @text = response error, it is will be errors: 324, 500, 404 or anythings else
          },
      dataType:'html',
      success: function(data) {
           alert(data);
           console.log(data);
           var decoding = sDecodeURI(data);
           console.log(decoding);
      },

      type: 'post'
   })

function sDecodeURI(vsStr) 
{
debugger
  try {
    if (typeof(vsStr) !== "string")
      return vsStr;

    var slSplit = vsStr.split('%u');
    if (slSplit.length === 1)
      return decodeURIComponent(vsStr);

    var sResult = new StringBuilder(decodeURIComponent(slSplit[0]));
    for (var i = 1; i < slSplit.length; ++i) {
      var sTmp = slSplit[i];
      var len = sTmp.length;
      if (len < 4)
        sResult.append("%u" + sTmp);
      else {
        var charCode = sTmp.substr(0, 4);
        sResult.append(String.fromCharCode(parseInt(charCode,16)));
        sResult.append(decodeURIComponent(sTmp.substr(4, sTmp.length-4)));
      }
    }
    return sResult.toString();
  }
  catch (e) {
    // Fallback to old-style encoding
    return unescape(vsStr);
  }
} 
   ;
}

</script></head>
<body>
<input onclick="ajaxreq()" type="button" value="Click me to load info!"></input>
<div id="info"></div>
</body>
</html>

如果我慢慢滑动，那么它的效果非常好。

Android代码（每个片段的代码相同.AsyncTask中的代码）：

E/AndroidRuntime: FATAL EXCEPTION: main
                Process: com.wilsapp.wilsapp, PID: 21319
                java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
                at com.wilsapp.wilsapp.Fragments.BuyerHomePageFragment9$DownloadImageTask.onPostExecute(BuyerHomePageFragment9.java:212)
                at com.wilsapp.wilsapp.Fragments.BuyerHomePageFragment9$DownloadImageTask.onPostExecute(BuyerHomePageFragment9.java:192)
                at android.os.AsyncTask.finish(AsyncTask.java:651)
                at android.os.AsyncTask.-wrap1(AsyncTask.java)
                at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:668)
                at android.os.Handler.dispatchMessage(Handler.java:102)
                at android.os.Looper.loop(Looper.java:148)
                at android.app.ActivityThread.main(ActivityThread.java:5417)
                at java.lang.reflect.Method.invoke(Native Method)
                at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Android onCreatView方法：

   protected void onPostExecute(Bitmap result) {
    try {
        ImageView img = (ImageView) getView().findViewById(R.id.ProductOneImageView);
        img.setImageBitmap(result);
    }catch (Exception e){
        ImageView img = (ImageView) getView().findViewById(R.id.ProductOneImageView);
        int id = getResources().getIdentifier("com.wilsapp.wilsapp:drawable/" + "error", null, null);
        img.setImageResource(id);
    }
}

我怎样才能避免NullPointerException？

Answer 1

ImageView img = (ImageView) getView().findViewById(R.id.ProductFiveImageView);

ImageView需要在onCreateView中初始化。你的案例getView()会返回null ...

Answer 2

使用onViewCreated方法而不是onCreateView添加初始化代码段。它将确保在您的观看次数膨胀后初始化imageview。

@Override
    public void onViewCreated(final View view, @Nullable Bundle savedInstanceState) {

 ImageView img = (ImageView) view.findViewById(R.id.ProductFiveImageView);
            img.setImageBitmap(result);

}

Answer 3

ImageView img = (ImageView) getView().findViewById(R.id.ProductFiveImageView);

hi您可以添加判断，getView是否为null，以及容错处理！

FragmentPagerAdapter中Fragment中的ImageView上的NullPointerException

3 个答案: