WithClassesMainActivity：
final Button b1= (Button) findViewById(R.id.button1);
final Button b2= (Button) findViewById(R.id.button2);
final Button b3= (Button) findViewById(R.id.button3);
final StoringClas sc=new StoringClas();
b1.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
String array1[]=new String[5];
array1[0]="a";array1[1]="b";array1[2]="y";array1[3]="g";
sc.writeToFile(array1);
}
});
b2.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
String[] ty =new String[5];
ty= sc.readFromFile();
b2.setText("ff"+ty[0]+ty[1]+ty[2]+ty[3]);
}
});
b3.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
String fs[]=new String[4];
try{
FileInputStream fIn = openFileInput("passd.txt");
InputStreamReader isr = new InputStreamReader(fIn);
/* Prepare a char-Array that will
* hold the chars we read back in. */
char[] inputBuffer = new char[6];
// Fill the Buffer with data from the file
isr.read(inputBuffer);
// Transform the chars to a String
String str=new String(inputBuffer);
fs[0]=str.substring(0,1);
fs[1]=str.substring(1,2);
fs[2]=str.substring(2,3);
fs[3]=str.substring(3,4);
b3.setText("g"+fs[0]+fs[1]+fs[2]+fs[3]);
} catch (IOException ioe)
{ioe.printStackTrace();
}}
});
存储类：
public class StoringClas extends Activity {
@SuppressLint("WorldReadableFiles")
@SuppressWarnings("deprecation")
public void writeToFile(String[] args){
try {
FileOutputStream fOut = openFileOutput("passd.txt",MODE_WORLD_READABLE);
OutputStreamWriter osw = new OutputStreamWriter(fOut);
// Write the string to the file
for(int i=0;i<=3;i++){
osw.write(args[i]);
}
//ensure that everything is
// really written out and close
osw.flush();
osw.close();}
catch(Exception Ex){}
}
public String[] readFromFile(){
String fs[]=new String[4];
try{
FileInputStream fIn = openFileInput("passd.txt");
InputStreamReader isr = new InputStreamReader(fIn);
/* Prepare a char-Array that will
* hold the chars we read back in. */
char[] inputBuffer = new char[6];
// Fill the Buffer with data from the file
isr.read(inputBuffer);
// Transform the chars to a String
String str=new String(inputBuffer);
fs[0]=str.substring(0,1);
fs[1]=str.substring(1,2);
fs[2]=str.substring(2,3);
fs[3]=str.substring(3,4);
} catch (IOException ioe)
{ioe.printStackTrace();
}
return fs;
}}
logcat的：
try{07-16 17:21:19.349: I/Adreno-EGL(4013): <qeglDrvAPI_eglInitialize:410>: EGL 1.4 QUALCOMM build:
AU_LINUX_ANDROID_LNX.LA.3.5.1_RB1.04.04.02.048.018_msm8610_LNX.LA.3.5.1_RB1__release_AU ()
07-16 17:21:19.349: I/Adreno-EGL(4013): OpenGL ES Shader Compiler Version: E031.24.00.08
07-16 17:21:19.349: I/Adreno-EGL(4013): Build Date: 03/07/14 Fri
07-16 17:21:19.349: I/Adreno-EGL(4013): Local Branch:
07-16 17:21:19.349: I/Adreno-EGL(4013): Remote Branch: quic/LNX.LA.3.5.1_RB1.1
07-16 17:21:19.349: I/Adreno-EGL(4013): Local Patches: NONE
07-16 17:21:19.349: I/Adreno-EGL(4013): Reconstruct Branch: AU_LINUX_ANDROID_LNX.LA.3.5.1_RB1.04.04.02.048.018
+ f2fd134 + NOTHING
07-16 17:21:19.399: D/OpenGLRenderer(4013): Enabling debug mode 0
07-16 17:21:21.251: D/AndroidRuntime(4013): Shutting down VM
07-16 17:21:21.251: W/dalvikvm(4013): threadid=1: thread exiting with uncaught exception (group=0x4165fd40)
07-16 17:21:21.254: E/AndroidRuntime(4013): FATAL EXCEPTION: main
07-16 17:21:21.254: E/AndroidRuntime(4013): Process: com.example.withclasses, PID: 4013
07-16 17:21:21.254: E/AndroidRuntime(4013): java.lang.NullPointerException
07-16 17:21:21.254: E/AndroidRuntime(4013): at
android.content.ContextWrapper.openFileInput(ContextWrapper.java:179)
07-16 17:21:21.254: E/AndroidRuntime(4013): at
com.example.withclasses.StoringClas.readFromFile(StoringClas.java:46)
07-16 17:21:21.254: E/AndroidRuntime(4013): at
com.example.withclasses.WithClassesMainActivity$2.onClick(WithClassesMainActivity.java:41)
07-16 17:21:21.254: E/AndroidRuntime(4013): at android.view.View.performClick(View.java:4456)
07-16 17:21:21.254: E/AndroidRuntime(4013): at android.view.View$PerformClick.run(View.java:18465)
07-16 17:21:21.254: E/AndroidRuntime(4013): at android.os.Handler.handleCallback(Handler.java:733)
07-16 17:21:21.254: E/AndroidRuntime(4013): at android.os.Handler.dispatchMessage(Handler.java:95)
07-16 17:21:21.254: E/AndroidRuntime(4013): at android.os.Looper.loop(Looper.java:136)
07-16 17:21:21.254: E/AndroidRuntime(4013): at android.app.ActivityThread.main(ActivityThread.java:5086)
07-16 17:21:21.254: E/AndroidRuntime(4013): at java.lang.reflect.Method.invokeNative(Native Method)
07-16 17:21:21.254: E/AndroidRuntime(4013): at java.lang.reflect.Method.invoke(Method.java:515)
07-16 17:21:21.254: E/AndroidRuntime(4013): at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
07-16 17:21:21.254: E/AndroidRuntime(4013): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
07-16 17:21:21.254: E/AndroidRuntime(4013): at dalvik.system.NativeStart.main(Native Method)}
首先，我点击button1写入文件。 但是，当我点击button2应用程序停止工作。 单击按钮3显示文件中没有存储任何内容。 代码有什么问题？ 在此先感谢.....
答案 0 :(得分：3)
您应该将Context（Activity扩展）传递给Util类中的静态方法，从而实现Write a File和Activity本身的干净解耦。
public class FileHelper {
public static void writeFile(Context context, ...) {}
}