Question

我想在扩展FragmentStatePagerAdapter的非Activity类中将String写入文件。

任何帮助？

我希望将String写入文件文件的方法如下所示：

Context ctx;

public void saveFile() {
    String xmlString = "";
    for (int i=0; i<mNumOfTabs; i++) {
        xmlString += days[i].toString() + "\n";
    }

    try{
        FileOutputStream fOut = ctx.openFileOutput("config.txt", MODE_WORLD_READABLE);

        OutputStreamWriter osw = new OutputStreamWriter(fOut);

        osw.write(xmlString);

        osw.flush();

        osw.close();
    }

    catch (IOException ioe)
    {
        ioe.printStackTrace();
    }

}

这是logcat：

  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.FileOutputStream android.content.Context.openFileOutput(java.lang.String, int)' on a null object reference
                                                                       at com.skolarac.skolarac.PageAdapter.saveFile(PageAdapter.java:78)
                                                                       at com.skolarac.skolarac.Day.onActivityResult(Day.java:165)
                                                                       at android.support.v4.app.FragmentActivity.onActivityResult(FragmentActivity.java:164)
                                                                       at android.app.Activity.dispatchActivityResult(Activity.java:6932)
                                                                       at android.app.ActivityThread.deliverResults(ActivityThread.java:4085)
                                                                       at android.app.ActivityThread.handleSendResult(ActivityThread.java:4132) 
                                                                       at android.app.ActivityThread.-wrap20(ActivityThread.java) 
                                                                       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1533) 
                                                                       at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                       at android.os.Looper.loop(Looper.java:154) 
                                                                       at android.app.ActivityThread.main(ActivityThread.java:6119) 
                                                                       at java.lang.reflect.Method.invoke(Native Method) 
                                                                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
                                                                       com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

Answer 1

问题是你的Context是null。

要解决此问题，您可以将上下文添加到类构造函数中：

public class MyClass extends FragmentStatePagerAdapter {
    Context ctx;
    public MyClass(Context context) { ctx = context;}

    ...
}

如何在FragmentStatePagerAdapter类中将String写入文件

1 个答案: