Question

我尝试将文件拼接到类，我有文件VKFile.java：

public class VKFile extends Activity {
public VKFile() {
    Log.d("BTCR", "Object VKFile created.");
}
public String read(String FILENAME){
    JSONArray result = new JSONArray();
    String line;
    InputStream inputStream;
    try {
        inputStream = openFileInput(FILENAME);
        InputStreamReader isr = new InputStreamReader(inputStream);
        BufferedReader reader = new BufferedReader(isr);

        while ((line = reader.readLine()) != null) {
            result = new JSONArray(line);
        }
        inputStream.close();
    } catch (JSONException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    Log.d("BTCR", "file.read, respond: "+result);
    return result.toString();
}

然后我在AuthorizedActivity.java中创建对象 - onCreate：

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.authorized_main);
    VKFile vkFile = new VKFile();
    vkFile.read("myfile");
}

运行此代码后，我的应用程序崩溃了这个日志：

java.lang.RuntimeException: Unable to start activity ComponentInfo{id.mirgorod.btcrussia/id.mirgorod.btcrussia.AuthorizedActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.FileInputStream android.content.Context.openFileInput(java.lang.String)' on a null object reference

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.FileInputStream android.content.Context.openFileInput(java.lang.String)' on a null object reference
at android.content.ContextWrapper.openFileInput(ContextWrapper.java:175)
at id.mirgorod.btcrussia.VKFile.read(VKFile.java:25)
at id.mirgorod.btcrussia.AuthorizedActivity.onCreate(AuthorizedActivity.java:129)

为什么会这样？如果我将类放在AuthorizedActivity.java中，相同的代码工作是完美的，但如果我尝试将代码放在其他类中，则给我错误。

Answer 1

Toumash，谢天谢地！

除非它们是静态的，否则不要从其他Activity类调用方法，现在你要创建更多的活动 - 它们很重。而是删除扩展活动或执行

public static String read(Context context , String FILENAME){

和

inputStream = context.openFileInput(FILENAME);

然后通过

使用它

VkFile.read(AuthorizedActivity.this,"myfile");

FileInputStream创建了类导入

1 个答案: