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在我的应用程序中，我有一个活动（MainActivity.java）和一个类（非活动类 - SubClass.java）。子类有一个 ProgressDialog。我将从 MainActivity 调用子类。

我的问题是如何使用来自活动类（MainActivity.java）的非活动类（SubClass.java）的 ProgressDialog

我在 setProgress() 和包声明处收到空指针异常错误。

我做了以下事情

1) 在 MainActivity 中，我使用构造函数为子类创建对象。

    SubClass pro = new SubClass(MainActivity.this);
    pro.call_fun();

2）在SubClass中：整体编码；

package com.progresss;  // Line No : 1 ; Shows Null Pointer Exception
public class SubClass {
Context context = null;
public static final int DIALOG_DOWNLOAD_PROGRESS = 0;
private NotificationManager notificationManager;
private Notification notification;
private int progress_val = 0;
private String fileURL = "http://xxxxx.com/folder/sampleproject.apk";
private String destination = null;
private ProgressDialog downloadProgressDialog;

public SubClass(MainActivity progress_DialiogActivity) {
    this.context = progress_DialiogActivity;
}

public void call_fun(){
    new DownloadFileAsync().execute(fileURL);
}

    //  Updated APK File Download Task.
class DownloadFileAsync extends AsyncTask<String, String, String> {
    @Override
    protected void onPreExecute() {
        super.onPreExecute();

        ((Activity) context).showDialog(DIALOG_DOWNLOAD_PROGRESS);
    //          Notification Coding     
        ...........
        notification.contentIntent = contentIntent;
    //          -------------------            
        notificationManager =(NotificationManager) context.getSystemService(context.NOTIFICATION_SERVICE);
        notificationManager.notify(0, notification);
    }

    @Override
    protected String doInBackground(String... aurl) {
        try {
    //              .......         
        } catch (Exception e) {
            Log.e("Error Report Download Manager", e.getMessage());
          }
        return null;
    }

    protected void onProgressUpdate(String... progress) {
         progress_val = Integer.parseInt(progress[0]);
         .......
         downloadProgressDialog.setProgress(Integer.parseInt(progress[0]));   // Line No : 100 ; Shows Null Pointer Exception
    }

    @Override
    protected void onPostExecute(String unused) {
        notificationManager.cancel(0);
    //          ((Activity) context).dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
        ((Activity) context).removeDialog(DIALOG_DOWNLOAD_PROGRESS);
        Log.e("Download", "Stop");

    //          Notification Coding     
        notificationManager = (NotificationManager) context.getSystemService(context.NOTIFICATION_SERVICE);
        .........
        notificationManager.notify(0, notification);

    //          Open The Install App Activity(Intent) Here.            
        ........
    }
} // Async Task Class End

    //our progress bar settings
protected Dialog onCreateDialog(int id) {
    switch (id) {
        case DIALOG_DOWNLOAD_PROGRESS: //we set this to 0
            downloadProgressDialog = new ProgressDialog(context);
            downloadProgressDialog.setMessage("Downloading file...");
            downloadProgressDialog.setMax(100);
            downloadProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
            downloadProgressDialog.setCancelable(false);
            downloadProgressDialog.show();
            return downloadProgressDialog;
        default:
            return null;
    }
  }
}

这是 LogCat 错误消息：

    FATAL EXCEPTION: main
java.lang.NullPointerException
at com.progresss.SubClass$DownloadFileAsync.onProgressUpdate(SubClass.java:100)
at com.progresss.SubClass$DownloadFileAsync.onProgressUpdate(SubClass.java:1)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:432)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:4627)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:521)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
at dalvik.system.NativeStart.main(Native Method)

进度对话框代码在活动类中运行良好。我猜 ProgressDialog 可能没有正确初始化。请帮我。

4

2 回答 2

1

onCreateDialog不执行。请将代码移至onPreExecuteMethod 。

onCreateDialog是回调方法，它只会在活动中被调用，在你的子类中它只是一个方法。

于 2012-10-06T07:29:08.893 回答
0

我遇到了同样的问题。在我将 onCreateDialog 移到 onPreExecute 之后，它不起作用。

我改成后解决了问题pro.call_fun()，pro.call_fun(MainActivity.this)然后downloadProgressDialog = new ProgressDialog(context)在pro.call_fun(MainActivity.this).

这个对我有用。

于 2014-11-05T10:33:01.300 回答