android - 从 .txt 文件加载数组？ (安卓)

Question

我已经四处搜索，但没能想出解决这个问题的办法。我的(第一个)问题是，我在 getLengthOfText(); 方法中的 FileInputStream instream = context.getApplicationContext().openFileInput(textname); 上遇到了 NPE。我已经调试并且正确的文件名似乎传递给了这个方法。我已经坚持了几个星期，真的希望它能工作(新手)。

这个方法正在被另一个类调用。此外，文件在数据/数据中，其他一切都应该如此。请帮忙!!-技巧

/***** this class takes a text file and loads it into an array **/

public class loadArray {

Context context;
textWriter textwriter;
public loadArray (Context cxt) {
     this.context = cxt;
     textwriter = new textWriter (cxt);
     context = cxt;
}

    FileInputStream instream;
    textWriter tw = new textWriter(context);
    String[] choiceAry, dummyAry;
    P p = new P(); // shared prefs helper
    String Choice;
    String comp = "notnull";

    int addChoiceCount, length;

    // Context context = this.getApplicationContext();

    public void buildDummies(int length) {
        // addChoiceCount = p.gisI("addChoiceCount");
        choiceAry = new String[length];
        p.pisI("length", length, context);

        // dummyAry = new String[100];

    }

    public Integer getLengthOfText(String textname)
            throws FileNotFoundException {// counts how many lines of text
        // DataInputStream dis = new DataInputStream(openFileInput("file.dat"));
        int length = 0;
        instream = context.getApplicationContext().openFileInput(textname);
        InputStreamReader inputreader = new InputStreamReader(instream);
        BufferedReader buffreader = new BufferedReader(inputreader);

        try {
            // while (!comp.equals(null)){
            while (buffreader.ready()) {
                String temp = buffreader.readLine();
                length++;
            }
            buffreader.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return length;
    }

    public String[] laft(String textname) throws FileNotFoundException {
        // loads a text file to an array...load array from text........
        length = getLengthOfText(textname);
        buildDummies(length);
        try {
            instream = context.getApplicationContext().openFileInput(textname);
            InputStreamReader inputreader = new InputStreamReader(instream);
            BufferedReader buffreader = new BufferedReader(inputreader);
            // load array from text
            for (int i = 0; i < (length); i++) {
                try {
                    Choice = buffreader.readLine();
                    choiceAry[i] = Choice;
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                buffreader.close();
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return choiceAry;

    }

    public String getOrderName() {
        // TODO Auto-generated method stub
        return null;
    }

}

感谢来自#android-dev 的 Leeds 和 billiard，我找到了答案

我正在做的也是从另一个没有扩展 Activity 的类调用 loadArry.. 所以它是 Activity >calling> 不扩展 Activity 的类 >calling> 不扩展 Activity 的类。不知何故，上下文丢失了。我基本上在顶部应用了类似的行

Context context;
textWriter textwriter;
public loadArray (Context cxt) {
     this.context = cxt;
     textwriter = new textWriter (cxt);
     context = cxt;

希望这能在将来为某人节省很多时间。

Answer 1

您在代码中把事情弄得太复杂了。最后，复杂的代码 = 更难调试。

我一直将文本文件加载到数组中。

考虑使用 java.util.StringTokenizer类或类 java.lang.String 中的 String split() 方法。

TenFour4 提出了另一个好点。

代码应该是这样的...

Context context;
textWriter textwriter;
public loadArray (Context cxt){
     this.context = cxt;
     textwriter = new textWriter (cxt);
}

--更新--

一个常见的错误是您尝试读取的文件没有正确关闭，因此每当您尝试访问仍然打开的文件时都会收到 NullPointerException。

例如

PrintWriter pw = new PrintWriter (new FileWriter (fileName));
pw.println ("This is output data: " + data);
//new loadArray ().getLengthOfText (fileName); //ERROR Throws NPE
pw.close(); //Make Sure you Close Before trying to read the file again!
new loadArray ().getLengthOfText (fileName); //Works like a charm :)