Question

我是本机android开发的新手。我正在使用android studio来开发应用。我正在使用tabbed-activity并使用3个标签。所有3个标签都有单独的classes和layouts，其名称如下图所示。

类和布局名称与图像中显示的相同。

我的标签包含以下功能。

在第一个标签上，我实现了一个google map v2，它显示了我当前的gps位置，上面有坐标和标记。
在第二个标签页上，我实施了一个camera，其中我放置了一个按钮和一个image view。按下按钮，相机将显示，当我拍照时，它显示我的图像视图。此图片也会保存到我的SD CARD中。
在第三个也是最后一个标签中，我添加了一个gird view，它将从SD CARD中获取这些图像并将其显示在网格上。

third tab我跟随此tutorial，因此我分别制作了2个helper和1个adapter课程。 2个辅助类是AppConstant和Utils，适配器名为GridViewImageAdapter，扩展了BaseAdapter。

以上3个（2个辅助和1个适配器）类都在我的pictures类中导入。

现在，当我第一次运行应用程序时，我能够看到我当前的位置。但是，当我点击camera标签时，它会转到Util类，当它找不到任何文件时应用程序崩溃。这不应该发生，因为我的Util类只导入pictures片段，而且与camera片段无关。以下是代码部分

Camera.java

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
  final View rootView = inflater.inflate(R.layout.camera, container, false);

    button = (Button)rootView.findViewById(R.id.getpicture);
    imageView = (ImageView)rootView.findViewById(R.id.imageView);

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            // Check permission for CAMERA
            if (ActivityCompat.checkSelfPermission(getActivity(), CAMERA)
                    != PackageManager.PERMISSION_GRANTED) {

                // Check Permissions Now
                // Callback onRequestPermissionsResult interceptado na Activity MainActivity
                ActivityCompat.requestPermissions(getActivity(),
                        new String[]{CAMERA},
                        Camera.REQUEST_CAMERA);

            }
            else {
                Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
                startActivityForResult(intent, CAPTURE_IMAGE_ACTIVITY_REQUEST_CODE );

            }


        }
    });



    return rootView;
}
//For saving image(s)
private void SaveImage(Bitmap finalBitmap) {

    String root = Environment.getExternalStorageDirectory().getAbsolutePath().toString();
    Log.v(getTag(), root);
    File myDir = new File(root + "/saved_images");
    myDir.mkdirs();
    Random generator = new Random();
    int n = 10000;
    n = generator.nextInt(n);
    String fname = "Image-" + n + ".jpg";
    File file = new File(myDir,fname);
    if (file.exists())file.delete();
    try {
        FileOutputStream out = new FileOutputStream(file);
        finalBitmap.compress(Bitmap.CompressFormat.JPEG,90,out);
        out.flush();
        out.close();


    } catch (Exception e) {
        e.printStackTrace();
    }
    //Toast.makeText(getContext(), "Image is saved", Toast.LENGTH_LONG).show();
}

以下是我的图片代码

Pictures.java

import com.example.accurat.faisal.adapter.GridViewImageAdapter;
import com.example.accurat.faisal.helper.Utils;
import com.example.accurat.faisal.helper.AppConstant;
//other imports
 @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.pictures, container, false);

    gridView = (GridView)rootView.findViewById(R.id.grid_view);
    utils = new Utils(getContext());

    // Initilizing Grid View
    InitilizeGridLayout();

    // loading all image paths from SD card
    imagePaths = utils.getFilePaths();

    // Gridview adapter

    adapter = new GridViewImageAdapter(getActivity(), imagePaths, columnWidth);
    /*adapter = new GridViewImageAdapter(Pictures.this, imagePaths,
            columnWidth);*/

    // setting grid view adapter
    gridView.setAdapter(adapter);


    return rootView;
}

private void InitilizeGridLayout() {

    Resources r = getResources();
    float padding = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,
            AppConstant.GRID_PADDING, r.getDisplayMetrics());

    columnWidth = (int) ((utils.getScreenWidth() - ((AppConstant.NUM_OF_COLUMNS + 1) * padding)) / AppConstant.NUM_OF_COLUMNS);

    gridView.setNumColumns(AppConstant.NUM_OF_COLUMNS);
    gridView.setColumnWidth(columnWidth);
    gridView.setStretchMode(GridView.NO_STRETCH);
    gridView.setPadding((int) padding, (int) padding, (int) padding,
            (int) padding);
    gridView.setHorizontalSpacing((int) padding);
    gridView.setVerticalSpacing((int) padding);
}

上述课程将访问helper和adapter方法。请参阅下面的帮助方法

Utils.java

public class Utils {

         // Reading file paths from SDCard
public ArrayList<String> getFilePaths() {
    ArrayList<String> filePaths = new ArrayList<String>();

    File directory = new File(
            android.os.Environment.getExternalStorageDirectory(),AppConstant.PHOTO_ALBUM);

    // check for directory
    if (directory.isDirectory()) {
        // getting list of file paths
        File[] listFiles = directory.listFiles();

        // Check for count
        if (listFiles.length > 0) {

            // loop through all files
            for (int i = 0; i < listFiles.length; i++) {

                // get file path
                String filePath = listFiles[i].getAbsolutePath();

                // check for supported file extension
                if (IsSupportedFile(filePath)) {
                    // Add image path to array list
                    filePaths.add(filePath);
                }
            }
        } else {
            // image directory is empty
            Toast.makeText(
                    _context,
                    AppConstant.PHOTO_ALBUM
                            + " is empty. Please load some images in it !",
                    Toast.LENGTH_LONG).show();
        }

    } else {
        AlertDialog.Builder alert = new AlertDialog.Builder(_context);
        alert.setTitle("Error!");
        alert.setMessage(AppConstant.PHOTO_ALBUM
                + " directory path is not valid! Please set the image directory name AppConstant.java class");
        alert.setPositiveButton("OK", null);
        alert.show();
    }

    return filePaths;
   }
}

此类中还有其他方法，但我只发布了上述方法，因为当我转到我的pictures标签时，此方法首先被调用，它适用于图片标签，但是当我转到我的{ {1}}选项卡再次调用上面的方法并调用它，因为我的相机类中没有任何东西可以访问辅助类。我不知道为什么会发生这种情况，因为所有课程都是分开的所以它不应该像这样工作，我得到camera

有关清单，请参阅下文

null exception

以下是错误

 <uses-permission android:name="com.example.accurat.faisal.permission.MAPS_RECEIVE"/>
<uses-permission android:name="android.permission.CAMERA" />
<uses-permission android:name="android.hardware.camera"/>
<uses-feature android:name="android.hardware.camera.autofocus" />
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="com.google.android.providers.gsf.permission.READ_GSERVICES"/>
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>
<uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>

FATAL EXCEPTION: main Process: com.example.accurat.faisal, PID: 25624 java.lang.NullPointerException: Attempt to get length of null array at com.example.accurat.faisal.helper.Utils.getFilePaths(Utils.java:42) at com.example.accurat.faisal.Pictures.onCreateView(Pictures.java:45) at android.support.v4.app.Fragment.performCreateView(Fragment.java:2184) at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1298) at android.support.v4.app.FragmentManagerImpl.moveFragmentsToInvisible(FragmentManager.java:2323) at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2136) at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2092) at android.support.v4.app.FragmentManagerImpl.execSingleAction(FragmentManager.java:1969) at android.support.v4.app.BackStackRecord.commitNowAllowingStateLoss(BackStackRecord.java:620) at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:143) at android.support.v4.view.ViewPager.populate(ViewPager.java:1268) at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:668) at android.support.v4.view.ViewPager.setCurrentItemInternal(ViewPager.java:630) at android.support.v4.view.ViewPager.setCurrentItem(ViewPager.java:611) at android.support.design.widget.TabLayout$ViewPagerOnTabSelectedListener.onTabSelected(TabLayout.java:2178) at android.support.design.widget.TabLayout.dispatchTabSelected(TabLayout.java:1155) at android.support.design.widget.TabLayout.selectTab(TabLayout.java:1148) at android.support.design.widget.TabLayout.selectTab(TabLayout.java:1118) at android.support.design.widget.TabLayout$Tab.select(TabLayout.java:1413) at android.support.design.widget.TabLayout$TabView.performClick(TabLayout.java:1523) at android.view.View$PerformClick.run(View.java:22596) 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:7325) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)是

Utlis.java:42

// check for directory if (directory.isDirectory()) { // getting list of file paths File[] listFiles = directory.listFiles(); // Check for count if (listFiles.length > 0) {// do the needful为Pictures.java:42

更新1

在// loading all image paths from SD card imagePaths = utils.getFilePaths();和Mike M我向每个帮助程序和适配器类导入Ruben2112的建议之后，还在READ_EXTERNAL_STORAGE中检查了listFiles课程如下

Utils

现在我的应用程序没有崩溃，但它仍然显示警报框上的错误，如下图所示

点击确定后，应用仍会运行

我坚持不懈，不知道该怎么做。任何帮助都将受到高度赞赏。

Answer 1

这不应该发生，因为我的Util类只导入了图片片段，而且与相机片段无关。

使用标签时要注意的一件重要事情是，正在打开的标签旁边的标签也会被加载。这样就可以加载标签，这样转换就更顺畅了，这是怎么回事可以滑动以转到下一个标签。

切换到android studio时，标签不能正常工作

1 个答案: