JPG文件選取器（Android）不起作用

Question

我從android-coding.blogspot得到JPG文件選取器

Java - 1.7; Android - 2.2;蝕。

package com.androidcustomdialog; 

import java.io.File; 

public class AndroidCustomDialogActivity extends Activity { 

Button buttonOpenDialog; 
Button buttonUp; 
TextView textFolder; 
ImageView image; 

String KEY_TEXTPSS = "TEXTPSS"; 
static final int CUSTOM_DIALOG_ID = 0; 

ListView dialog_ListView; 

File root; 
File curFolder; 

private List<String> fileList = new ArrayList<String>(); 

    /** Called when the activity is first created. */ 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.main); 

     image = (ImageView)findViewById(R.id.image); 

     buttonOpenDialog = (Button)findViewById(R.id.opendialog); 
     buttonOpenDialog.setOnClickListener(new Button.OnClickListener(){ 
      public void onClick(View arg0) { 
       showDialog(CUSTOM_DIALOG_ID); 
      }}); 

     root = new File(Environment.getExternalStorageDirectory().getAbsolutePath()); 
     curFolder = root; 
    } 

@Override 
protected Dialog onCreateDialog(int id) { 

    Dialog dialog = null; 

    switch(id) { 
    case CUSTOM_DIALOG_ID: 
     dialog = new Dialog(AndroidCustomDialogActivity.this); 
     dialog.setContentView(R.layout.dialoglayout); 
     dialog.setTitle("Select JPG"); 

     dialog.setCancelable(true); 
     dialog.setCanceledOnTouchOutside(true); 

     textFolder = (TextView)dialog.findViewById(R.id.folder); 

     buttonUp = (Button)dialog.findViewById(R.id.up); 
     buttonUp.setOnClickListener(new OnClickListener(){ 
      public void onClick(View v) { 
       ListDir(curFolder.getParentFile()); 
      }}); 

     //Prepare ListView in dialog 
     dialog_ListView = (ListView)dialog.findViewById(R.id.dialoglist); 
     dialog_ListView.setOnItemClickListener(new OnItemClickListener(){ 
      public void onItemClick(AdapterView<?> parent, View view, 
        int position, long id) { 
       File selected = new File(fileList.get(position)); 
       if(selected.isDirectory()){ 
        ListDir(selected); 
       }else { 
        Toast.makeText(AndroidCustomDialogActivity.this, 
          selected.toString() + " selected", 
          Toast.LENGTH_LONG).show(); 
        dismissDialog(CUSTOM_DIALOG_ID); 

        Bitmap bm = BitmapFactory.decodeFile(selected.getAbsolutePath()); 
        image.setImageBitmap(bm); 
     }}}); 
     break; 
    } 
    return dialog; 
} 

@Override 
protected void onPrepareDialog(int id, Dialog dialog, Bundle bundle) 
{ 
    super.onPrepareDialog(id, dialog, bundle); 
    switch(id) { 
    case CUSTOM_DIALOG_ID: 
     ListDir(curFolder); 
     break; 
    } 
} 

void ListDir(File f) 
{ 
    if(f.equals(root)){ 
    buttonUp.setEnabled(false); 
    }else{       //115 134 54 
    buttonUp.setEnabled(true); 
    } 

    curFolder = f; 
    textFolder.setText(f.getPath()); 

    File[] files = f.listFiles(); 
    fileList.clear(); 
    for (File file : files) 
    { 
     if(file.isDirectory()){ 
     fileList.add(file.getPath()); 
     }else{ 
     Uri selectedUri = Uri.fromFile(file); 
     String fileExtension 
     = MimeTypeMap.getFileExtensionFromUrl(selectedUri.toString()); 
     if(fileExtension.equalsIgnoreCase("jpg")){ 
     fileList.add(file.getPath()); 
     } 
     } 
    } 

    ArrayAdapter<String> directoryList 
    = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, fileList); 
    dialog_ListView.setAdapter(directoryList); 
} 

有沒有錯誤的開始之前，但按「加載JPG」這是「意外停止」之後。日誌是：

07-24 07:43:10.328: E/AndroidRuntime(5634): FATAL EXCEPTION: main 
07-24 07:43:10.328: E/AndroidRuntime(5634): java.lang.NullPointerException 
07-24 07:43:10.328: E/AndroidRuntime(5634): at com.androidcustomdialog.AndroidCustomDialogActivity.ListDir(AndroidCustomDialogActivity.java:129) 
07-24 07:43:10.328: E/AndroidRuntime(5634): at com.androidcustomdialog.AndroidCustomDialogActivity.onPrepareDialog(AndroidCustomDialogActivity.java:111) 
07-24 07:43:10.328: E/AndroidRuntime(5634): at android.app.Activity.showDialog(Activity.java:2555) 
07-24 07:43:10.328: E/AndroidRuntime(5634): at android.app.Activity.showDialog(Activity.java:2514) 
07-24 07:43:10.328: E/AndroidRuntime(5634): at com.androidcustomdialog.AndroidCustomDialogActivity$1.onClick(AndroidCustomDialogActivity.java:54) 
07-24 07:43:10.328: E/AndroidRuntime(5634): at android.view.View.performClick(View.java:2408) 
07-24 07:43:10.328: E/AndroidRuntime(5634): at android.view.View$PerformClick.run(View.java:8816) 
07-24 07:43:10.328: E/AndroidRuntime(5634): at android.os.Handler.handleCallback(Handler.java:587) 
07-24 07:43:10.328: E/AndroidRuntime(5634): at android.os.Handler.dispatchMessage(Handler.java:92) 
07-24 07:43:10.328: E/AndroidRuntime(5634): at android.os.Looper.loop(Looper.java:123) 
07-24 07:43:10.328: E/AndroidRuntime(5634): at android.app.ActivityThread.main(ActivityThread.java:4627) 
07-24 07:43:10.328: E/AndroidRuntime(5634): at java.lang.reflect.Method.invokeNative(Native Method) 
07-24 07:43:10.328: E/AndroidRuntime(5634): at java.lang.reflect.Method.invoke(Method.java:521) 
07-24 07:43:10.328: E/AndroidRuntime(5634): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
07-24 07:43:10.328: E/AndroidRuntime(5634): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
07-24 07:43:10.328: E/AndroidRuntime(5634): at dalvik.system.NativeStart.main(Native Method) 

Answer 1

錯誤明顯是印刷在日誌中 - 你已經有了一個NullPointerException處出現線129

不匹配但是你打印的源線，所以很難確切地識別錯誤。我的猜測是f中的ListDir爲空，或者f.listFiles()返回null，因爲curFile不是有效的目錄。