点击发送后图片查看大图的实现思路

图片加载与显示策略

最新推荐文章于 2024-11-25 21:30:00 发布

原创最新推荐文章于 2024-11-25 21:30:00 发布 · 669 阅读

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#android #图片显示

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本文介绍了一种通过Intent传递图片大小图key，并利用缓存显示图片的方法。在缓存中有大图时直接显示，若无则先展示小图并后台下载大图。此方法适用于移动端应用的大图预览场景。

点击发送后图片查看大图的实现思路：

1.通过Intent传递key,包括大图和小图的key

2.通过大图的key从缓存中查询图片的Bitmap

3.如果缓存中已经有了，则直接显示

4.如果缓存中没有，则先显示小图，然后下载大图后再显示

主要代码如下：



/**
 * Created by zhanghuirong on 2016/2/26.
 */
public class ImageDisplayActivity extends Activity {

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);

		Intent intent = getIntent();

		mLocalHandler = new LocalHandler();
		mLocalHandler.registerHandleCallback(mCallback);

		mImageView = (ImageView)findViewById(R.id.image_view);
		
		ViewTreeObserver viewTreeObserver = mImageView.getViewTreeObserver();
		viewTreeObserver.addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
			@Override
			public void onGlobalLayout() {
				mImageView.getViewTreeObserver().removeGlobalOnLayoutListener(this);
				if (intent != null) {
					String smallImageKey = intent.getStringExtra(SMALL_IMAGE_KEY);
					String imageKey = intent.getStringExtra(IMAGE_KEY);
					Bitmap bitmap = ImageMsgManager.getCacheBitmap(imageKey);
					if (bitmap == null) {
						Bitmap smallBitmap = ImageMsgManager.getCacheBitmap(smallImageKey);
						if (smallBitmap != null) {
							showImage(smallBitmap);
						}
						downloadImage(imageKey);
					} else {
						showImage(bitmap);
					}
				}
			}
		});
	}

	private void downloadImage(String imageKey) {
		ImageMsgManager.ImgageDownloadListener listener = new ImageMsgManager.ImgageDownloadListener() {

			@Override
			public void onSuccess(final Bitmap img) {
				ImageMsgManager.setCacheBitmap(imageKey, img);
				if (mLocalHandler != null) {
					mLocalHandler.sendMessageDelayed(mLocalHandler.obtainMessage(CALLBACK_DOWNLOAD_BIG_IMAGE_SUCCESS, imageKey), 1000);
				}
			}

			@Override
			public void onFailure() {

			}
		};
		String filePath = ImageBitmapUtil.getBitmapCacheDirByUrl(ctx, imageKey);
		ImageMsgManager.downloadImage(imageKey, filePath, listener);
	}

	private void showImage(Bitmap bitmap) {
		if (bitmap == null || bitmap.isRecycled()) {
			return;
		}

		int viewWidth = mImageView.getMeasuredWidth();
		int viewHeight = mImageView.getMeasuredHeight();
		int imgWidth = bitmap.getWidth();
		int imgHeight = bitmap.getHeight();

		float scale = 1;
		float baseX = 0;
		float baseY = 0;

		float scaleX = (float) viewWidth / imgWidth;
		float scaleY = (float) viewHeight / imgHeight;

		if (scaleX < scaleY) { //按宽度缩放
			scale = scaleX;
			baseY = ((viewHeight - (imgHeight * scale)) / 2);
		} else if (scaleX > scaleY) { //按高度缩放
			scale = scaleY;
			baseX = ((viewWidth - (imgWidth * scale)) / 2);
		}

		Matrix matrix = new Matrix();
		matrix.set(mImageView.getImageMatrix());
		matrix.postScale(scale, scale);
		matrix.postTranslate(baseX, baseY);
		mImageView.setImageMatrix(matrix);
		mImageView.setImageBitmap(bitmap);
	}

	@Override
	protected void onDestroy() {
		super.onDestroy();
		mLocalHandler.unRegisterHandleCallback();
		mLocalHandler = null;
	}

	private Handler.Callback mCallback = new Handler.Callback() {
		@Override
		public boolean handleMessage(Message msg) {
			switch (msg.what) {
				case CALLBACK_DOWNLOAD_BIG_IMAGE_SUCCESS:
					String imageKey = (String) msg.obj;
					Bitmap bitmap = ImageMsgManager.getCacheBitmap(imageKey);
					showImage(bitmap);
					break;
				default:
					break;
			}
			return false;
		}
	};
}