在我的应用程序中读取/写入文件时出错

Question

MainActivity：

package com.example.jaypatel.file;

import android.content.Context;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.nio.Buffer;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    public void writeData(View view)
    {
        BufferedWriter bufferWriter = null;
        try {
            FileOutputStream fileOutputStream = openFileOutput("testFile", Context.MODE_PRIVATE);
            bufferWriter = new BufferedWriter(new OutputStreamWriter(fileOutputStream));
            bufferWriter.write(((EditText)this.findViewById(R.id.editText1)).getText().toString());
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally
        {
            try {
                bufferWriter.close();
            }catch (IOException e){
                e.printStackTrace();
            }
        }
    }

    public void readData(View view)
    {
        BufferedReader bufferedReader = null;
        StringBuilder result = new StringBuilder();
        try {
            FileInputStream fileInputStream = openFileInput("testFile");
            BufferedReader bufferReader = new BufferedReader(new InputStreamReader(fileInputStream));
            String line;
            while ((line=bufferReader.readLine())!=null){
                result.append(line + "\r\n");
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e){
            e.printStackTrace();
        }finally {
            try {
                bufferedReader.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        ((EditText)this.findViewById(R.id.editText2)).setText(result);
    }
}

错误日志：

FATAL EXCEPTION: main
Process: com.example.jaypatel.file, PID: 3382
java.lang.IllegalStateException: Could not execute method for android:onClick
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
    at android.view.View.performClick(View.java:4438)
    at android.view.View$PerformClick.run(View.java:18422)
    at android.os.Handler.handleCallback(Handler.java:733)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:136)
    at android.app.ActivityThread.main(ActivityThread.java:5017)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:515)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
    at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.reflect.InvocationTargetException
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:515)
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
    at android.view.View.performClick(View.java:4438) 
    at android.view.View$PerformClick.run(View.java:18422) 
    at android.os.Handler.handleCallback(Handler.java:733) 
    at android.os.Handler.dispatchMessage(Handler.java:95) 
    at android.os.Looper.loop(Looper.java:136) 
    at android.app.ActivityThread.main(ActivityThread.java:5017) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:515) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
    at dalvik.system.NativeStart.main(Native Method) 
Caused by: java.lang.NullPointerException
    at com.example.jaypatel.file.MainActivity.readData(MainActivity.java:65)
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:515) 
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) 
    at android.view.View.performClick(View.java:4438) 
    at android.view.View$PerformClick.run(View.java:18422) 
    at android.os.Handler.handleCallback(Handler.java:733) 
    at android.os.Handler.dispatchMessage(Handler.java:95) 
    at android.os.Looper.loop(Looper.java:136) 
    at android.app.ActivityThread.main(ActivityThread.java:5017) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:515) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595) 
    at dalvik.system.NativeStart.main(Native Method)

 

Answer 1

我收到了你的错误，因为你声明了两个时间缓冲区读取器，因此它显示空指针异常，

只需浏览我下面编辑的代码即可

  public void readData(View view)
  {
     BufferedReader bufferedReader = null;
     StringBuilder result = new StringBuilder();
     try {
         FileInputStream fileInputStream = openFileInput("testFile");
         bufferReader = new BufferedReader(new InputStreamReader(fileInputStream));
         String line;
          while ((line=bufferReader.readLine())!=null){
              result.append(line + "\r\n");
         }
      } catch (FileNotFoundException e) {
        e.printStackTrace();
      } catch (IOException e){
        e.printStackTrace();
     }finally {
        try {
            bufferedReader.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    ((EditText)this.findViewById(R.id.editText2)).setText(result);
}

Answer 2

问题在于editText2，你还没有初始化它。我希望您执行以下操作：

1. 声明一个私有字段private EditText editText;

2. 像这样在onCreate()方法中绑定视图(editText2)

   editText = (EditText) findViewById(R.id.editText2);

3. 在readData() 内而不是
   
   ((EditText)this.findViewById(R.id.editText2)).setText(result);
   
   使用这行代码：

   this.editText.setText(result);