Question

在我的活动中，用户可以拍摄照片，然后将拍摄图像设置为gridview.And gridview中有一些图像（捕获图像）和2个编辑文本。现在我想将信息保存在2个编辑文本中共享onPause（）中的首选项文件;并将共享首选项文件中的值返回到onResume中的edittext。

这是我的代码

public class MainActivity extends Activity {

private Button btPhoto, btSave;
private GridView gridview;
private File imgFile;
private String path;
private ArrayList<File> List_File;
private static final int imageCode = 100;
private Context context;
SharedPreferences preference;
SharedPreferences.Editor editor;




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

    btPhoto = (Button) findViewById(R.id.btPhoto);
    btSave = (Button) findViewById(R.id.bt_save);
    gridview = (GridView) findViewById(R.id.gridview);

    path = "/TongFolder/";
    context = this;
    List_File = new ArrayList<File>();
    File imgDir = new File(Environment.getExternalStorageDirectory()+path);
    imgDir.mkdirs();
    boolean check = imgDir.isDirectory();
    if(check == true){
    btPhoto.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            capture();

        }
    });
    }else{
        System.out.println("not create");
    }
 }


public void capture(){
    Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
    imgFile = new File(Environment.getExternalStorageDirectory()+path, 
            "img_"+System.currentTimeMillis()+".jpg");
    intent.putExtra(MediaStore.EXTRA_OUTPUT, Uri.fromFile(imgFile));
    startActivityForResult(intent, imageCode);
}

protected void onActivityResult(int requestCode, int resultCode, Intent data){

    if(requestCode == imageCode && resultCode == RESULT_OK){

        //add path to arrayList
        List_File.add(imgFile);
        for (File file : List_File) {
            String showPath = file.getPath();
            System.out.println(showPath);
        }

        gridview.setAdapter(new gridViewAdapter(context, List_File));


    }

}

public void onPause(){

    super.onPause();
      //initialize
    preference = getPreferences(Context.MODE_PRIVATE);
    EditText edit_num = new EditText(getApplicationContext());
    EditText edit_info = new EditText(getApplicationContext());

    //count child of gridview
    int size = gridview.getChildCount();
    System.out.println("size_"+size);
    if(size == 0){

    }else{
        ViewGroup child_grid = (ViewGroup) gridview.getChildAt(size);
        //get editText in child_gridview
        edit_num = (EditText) child_grid.findViewById(R.id.editText_num);
        edit_info = (EditText) child_grid.findViewById(R.id.editText_info);

        String num = edit_num.getText().toString();
        String info = edit_info.getText().toString();

        //save data to sharedpreference file
        editor = preference.edit();
        editor.putString("number_recipe_"+size, num);
        editor.putString("info_recipe_"+size, info);
        editor.commit();

        System.out.println("data in position "+size+" is "+num+"and"+info);
    }
}

public void onResume(){
    super.onResume();

    //initialize
    EditText edit_num = new EditText(getApplicationContext());
    EditText edit_info = new EditText(getApplicationContext());

    //count child in gridview
    int size = gridview.getChildCount();
    System.out.println("onResume_child in gridview have "+size);

    //for loop to put data in shared preference to edittext(2)
    for(int i = 0; i<size; i++){
        ViewGroup child_grid = (ViewGroup) gridview.getChildAt(i);
        //findviewById edittext in childAt (i)
        edit_num = (EditText) child_grid.findViewById(R.id.editText_num);
        edit_info = (EditText) child_grid.findViewById(R.id.editText_info);
        //get value from shared preference file and set text to editText
        String number = preference.getString("number_recipe_"+i, null);
        String information = preference.getString("info_recipe_"+i, null);

        edit_num.setText(number);
        edit_info.setText(information);
    }

}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

}

这是我的logcat

02-19 21:11:51.136: E/AndroidRuntime(15891): FATAL EXCEPTION: main
02-19 21:11:51.136: E/AndroidRuntime(15891): java.lang.RuntimeException: Unable to pause activity {com.example.imagecapture/com.example.imagecapture.MainActivity}: java.lang.NullPointerException
02-19 21:11:51.136: E/AndroidRuntime(15891):    at android.app.ActivityThread.performPauseActivity(ActivityThread.java:2902)
02-19 21:11:51.136: E/AndroidRuntime(15891):    at android.app.ActivityThread.performPauseActivity(ActivityThread.java:2858)
02-19 21:11:51.136: E/AndroidRuntime(15891):    at android.app.ActivityThread.handlePauseActivity(ActivityThread.java:2836)
02-19 21:11:51.136: E/AndroidRuntime(15891):    at android.app.ActivityThread.access$900(ActivityThread.java:140)
02-19 21:11:51.136: E/AndroidRuntime(15891):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1248)
02-19 21:11:51.136: E/AndroidRuntime(15891):    at android.os.Handler.dispatchMessage(Handler.java:99)
02-19 21:11:51.136: E/AndroidRuntime(15891):    at android.os.Looper.loop(Looper.java:137)
02-19 21:11:51.136: E/AndroidRuntime(15891):    at android.app.ActivityThread.main(ActivityThread.java:4921)
02-19 21:11:51.136: E/AndroidRuntime(15891):    at java.lang.reflect.Method.invokeNative(Native Method)
02-19 21:11:51.136: E/AndroidRuntime(15891):    at java.lang.reflect.Method.invoke(Method.java:511)
02-19 21:11:51.136: E/AndroidRuntime(15891):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038)
02-19 21:11:51.136: E/AndroidRuntime(15891):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805)
02-19 21:11:51.136: E/AndroidRuntime(15891):    at dalvik.system.NativeStart.main(Native Method)
02-19 21:11:51.136: E/AndroidRuntime(15891): Caused by: java.lang.NullPointerException
02-19 21:11:51.136: E/AndroidRuntime(15891):    at com.example.imagecapture.MainActivity.onPause(MainActivity.java:123)
02-19 21:11:51.136: E/AndroidRuntime(15891):    at android.app.Activity.performPause(Activity.java:5304)
02-19 21:11:51.136: E/AndroidRuntime(15891):    at android.app.Instrumentation.callActivityOnPause(Instrumentation.java:1240)
02-19 21:11:51.136: E/AndroidRuntime(15891):    at android.app.ActivityThread.performPauseActivity(ActivityThread.java:2889)
02-19 21:11:51.136: E/AndroidRuntime(15891):    ... 12 more

谢谢

Answer 1

我在代码中看到一个可能导致NullPointerException的错误。

在下面的代码中，getChildCount返回ViewGroup中的子项数量，但不返回最高子项索引。你必须使用 size - 1 来获得最后一个孩子！

<强>错误

int size = gridview.getChildCount();
ViewGroup child_grid = (ViewGroup) gridview.getChildAt(size);

<强>正确

int size = gridview.getChildCount();
ViewGroup child_grid = (ViewGroup) gridview.getChildAt(size - 1);

无法暂停活动java.lang.NullPointerException

1 个答案: