我正在尝试将我的设置保存在文件中，但总是在写入文件时，我得到NullPointerException
02-05 09:54:21.021 4102-4102/? I/art: Not late-enabling -Xcheck:jni (already on)
02-05 09:54:21.092 4102-4102/com.example.andy.newshit W/System: ClassLoader referenced unknown path: /data/app/com.example.andy.newshit-1/lib/x86_64
02-05 09:54:22.588 4102-4180/com.example.andy.newshit D/OpenGLRenderer: Use EGL_SWAP_BEHAVIOR_PRESERVED: true
02-05 09:54:22.618 4102-4180/com.example.andy.newshit I/OpenGLRenderer: Initialized EGL, version 1.4
02-05 09:54:22.630 4102-4180/com.example.andy.newshit W/EGL_emulation: eglSurfaceAttrib not implemented
02-05 09:54:22.630 4102-4180/com.example.andy.newshit W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0x7f76333968c0, error=EGL_SUCCESS
02-05 09:54:26.746 4102-4102/com.example.andy.newshit W/art: Before Android 4.1, method int android.support.v7.widget.ListViewCompat.lookForSelectablePosition(int, boolean) would have incorrectly overridden the package-private method in android.widget.ListView
02-05 09:54:26.795 4102-4180/com.example.andy.newshit W/EGL_emulation: eglSurfaceAttrib not implemented
02-05 09:54:26.795 4102-4180/com.example.andy.newshit W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0x7f7633396c80, error=EGL_SUCCESS
02-05 09:54:28.031 4102-4180/com.example.andy.newshit W/EGL_emulation: eglSurfaceAttrib not implemented
02-05 09:54:28.031 4102-4180/com.example.andy.newshit W/OpenGLRenderer: Failed to set EGL_SWAP_BEHAVIOR on surface 0x7f7626d5a640, error=EGL_SUCCESS
02-05 09:54:28.142 4102-4180/com.example.andy.newshit E/Surface: getSlotFromBufferLocked: unknown buffer: 0x7f7637d5a780
02-05 09:54:28.145 4102-4180/com.example.andy.newshit E/Surface: getSlotFromBufferLocked: unknown buffer: 0x7f7637d59e50
02-05 09:54:28.146 4102-4180/com.example.andy.newshit D/OpenGLRenderer: endAllStagingAnimators on 0x7f7626dba000 (ListPopupWindow$DropDownListView) with handle 0x7f7626edad00
02-05 09:54:32.604 4102-4102/com.example.andy.newshit D/AndroidRuntime: Shutting down VM
02-05 09:54:32.604 4102-4102/com.example.andy.newshit E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.andy.newshit, PID: 4102 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 android.content.ContextWrapper.openFileOutput(ContextWrapper.java:183)
at com.example.andy.newshit.Filehandling.writeFile(Filehandling.java:20)
at com.example.andy.newshit.IPandPort.setIP(IPandPort.java:45)
at com.example.andy.newshit.SettingsActivity$1.onClick(SettingsActivity.java:29)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
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)
这是我必须处理文件的类
package com.example.andy.newshit;
import android.content.Context;
import android.support.v7.app.AppCompatActivity;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
/**
* Created by buddy on 05.02.16.
*/
public class Filehandling extends AppCompatActivity{
public void writeFile(String Filename, String Text) throws IOException {
FileOutputStream fos = openFileOutput(Filename, Context.MODE_PRIVATE);
fos.write(Text.getBytes());
fos.close();
}
public void readFile(String File) throws IOException {
try {
BufferedReader inputReader = new BufferedReader(new InputStreamReader(openFileInput(File)));
String inputString;
StringBuffer stringBuffer = new StringBuffer();
inputString = inputReader.readLine();
}
catch (IOException e){
e.printStackTrace();
}
}
}
我真的希望能得到一些帮助。
答案 0 :(得分：1)
100％肯定＆amp;经过测试.. 使用此代码文件将从设备读取：
public void readFile(String File) throws IOException {
File cacheDir = new File(android.os.Environment.getExternalStorageDirectory(), "/stackover");
//for make the directory if not exist
if (!cacheDir.exists())
cacheDir.mkdirs();
File f = new File(cacheDir, File);
FileInputStream fin = new FileInputStream(f);
InputStreamReader isr = new InputStreamReader(fin);
char[] ib = new char[1000];
String str ="";
int cr ;
while( (cr=isr.read(ib))>0)
{
String s = String.copyValueOf(ib,0,cr);
str+=s;
ib = new char[1000];
}
isr.close();
Toast.makeText(getApplicationContext(),str+"", Toast.LENGTH_SHORT).show();
}
}
答案 1 :(得分：0)
从堆栈中看，很明显你是从Filehanlding调用SettingsActivity活动方法。
你不能这样做。为了使用与Context相关的方法，Filehandling需要是一个创建的Activity。
为了从SettingsActivity的OnClickListener中执行您想要的操作，您必须使Filehandling成为一个接收工作Activity的Context的util类。
public final class Filehandling {
private Filehandling() {
}
public static void writeFile(Context context, String Filename, String Text) throws IOException {
FileOutputStream fos = context.openFileOutput(Filename, Context.MODE_PRIVATE);
fos.write(Text.getBytes());
fos.close();
}
public sttaic void readFile(Context context, String File) throws IOException {
try {
BufferedReader inputReader = new BufferedReader(new InputStreamReader(context.openFileInput(File)));
String inputString;
StringBuffer stringBuffer = new StringBuffer();
inputString = inputReader.readLine();
}
catch (IOException e){
e.printStackTrace();
}
}
}
public class IPandPort {
public static void setIp(Context context) {
try {
FileHandling.writeFile(context, "file.txt", "yourtext");
} catch (IOException e) {
// TODO
}
}
}
从SettingsActivity，您可以这样做
btn.setOnClickListener(bew View.OnClickListener() {
@Override
public void onClick(View v) {
// Pass a Context as SettingsActivity from anonymous listener. Note if it's not an inner class you can just pass "this"
IPandPort.setIp(SettingsActivity.this);
}
});
答案 2 :(得分：0)
100％确定
使用此代码文件将使用satyam文件夹写入您的Internel存储中。 试着快乐编码...
public void writeFile(String Filename, String Text) throws IOException {
File cacheDir = new File(android.os.Environment.getExternalStorageDirectory(), "/satyam");
//for make the directory if not exist
if (!cacheDir.exists())
cacheDir.mkdirs();
File f = new File(cacheDir, Filename);
FileOutputStream fout = new FileOutputStream(f);
OutputStreamWriter osw = new OutputStreamWriter(fout);
osw.write(Text);
osw.flush();
osw.close();
Toast.makeText(getApplicationContext(),"Success",Toast.LENGTH_SHORT).show();
}
答案 3 :(得分：-1)
首先尝试检查您想要阅读的file是否存在
File data = new File(filePath);
if(data.exists()) {
// your code to read file
}
更新
正确地将数据写入文件：
public void writeFile(String Filename, String Text) throws IOException {
String path = Environment.getExternalStorageDirectory() + File.separator + "/"+Filename + File.separator;
File dir = new File(path);
if (!dir.exists()) {
dir.mkdirs();
}
File data = new File(path);
if (!data.createNewFile()) {
data.delete();
data.createNewFile();
}
ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(data));
objectOutputStream.writeObject(Text.getBytes());
objectOutputStream.close();
}