Android编程权威指南（第2版）—第16章挑战练习

16.7挑战练习：优化照片显示

(1)新建dialog_photo.xml

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"              android:orientation="vertical"              android:layout_width="match_parent"              android:layout_height="match_parent">    <ImageView        android:id="@+id/crime_photo_detail"        android:layout_width="match_parent"        android:layout_height="match_parent"        /></LinearLayout>

(2)新建PhotoDetailFragment.java

public class PhotoDetailFragment extends DialogFragment {    private static final String ARG_File = "file";    private ImageView mPhotoView;    public static PhotoDetailFragment newInstance(File file) {        Bundle args = new Bundle();        args.putSerializable(ARG_File, file);        PhotoDetailFragment fragment = new PhotoDetailFragment();        fragment.setArguments(args);        return fragment;    }    @NonNull    @Override    public Dialog onCreateDialog(Bundle savedInstanceState) {        File file = (File) getArguments().getSerializable(ARG_File);        View v = LayoutInflater.from(getActivity())                .inflate(R.layout.dialog_photo, null);        mPhotoView = (ImageView) v.findViewById(R.id.crime_photo_detail);        Bitmap bitmap = PictureUtils.getScaledBitmap(                file.getPath(), getActivity());        mPhotoView.setImageBitmap(bitmap);        return new AlertDialog.Builder(getActivity())                .setView(v)                //.setTitle(R.string.date_picker_title)                .setPositiveButton(android.R.string.ok, null)                .create();    }}

(3)修改CrimeFragment.java

private static final int REQUEST_PHOTO = 3;private static final String DIALOG_PHOTO = "DialogPhoto";

onCreateView增加处理

mPhotoView = (ImageView) v.findViewById(R.id.crime_photo);        mPhotoView.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View view) {                if (mPhotoFile == null || !mPhotoFile.exists()) {                    mPhotoView.setImageDrawable(null);                } else {                    FragmentManager manager = getFragmentManager();                    PhotoDetailFragment dialog = PhotoDetailFragment.newInstance(mPhotoFile);                    dialog.setTargetFragment(CrimeFragment.this, REQUEST_PHOTO);                    dialog.show(manager, DIALOG_PHOTO);                }            }        });        updatePhotoView();

16.8 挑战练习：优化缩略图加载

修改CrimeFragment.java

(1)updatePhotoView,调用带宽高参数的getScaledBitmap

private void updatePhotoView(int width, int height) {        if (mPhotoFile == null || !mPhotoFile.exists()) {            mPhotoView.setImageDrawable(null);        } else {            Bitmap bitmap = PictureUtils.getScaledBitmap(                    mPhotoFile.getPath(), width, height); // change this one            mPhotoView.setImageBitmap(bitmap);        }    }

(2)onCreateView加上

mPhotoObserver = mPhotoView.getViewTreeObserver();        mPhotoObserver.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {            @Override            public void onGlobalLayout() {                updatePhotoView(mPhotoView.getWidth(), mPhotoView.getHeight());            }        });        return v;

(3)修改onActivityResult，不然返回拍完照片返回CrimeFragment的时候会显示不出略缩图

else if (requestCode == REQUEST_PHOTO) {                    updatePhotoView(mPhotoView.getWidth(), mPhotoView.getHeight());        }

参考：点击打开链接

上述代码运行无误，可以达到效果，但是OnGlobalLayoutListener的原理还没有太搞懂，只知道可以通过这个方式获取视图的宽和高，待以后深入学习后再加补充。