Android 获取最近应用的缩略图

最近有项需求是获取应用的缩略,用于在动画时显示。因此就对此块知识简要了解了一下。


在android中获取视频文件的缩略图有三种方法:

1.从媒体库中查询
新视频增加后需要SDCard重新扫描才能给新增加的文件添加缩略图,灵活性差,而且不是很稳定,适合简单应用
2. android 2.2以后使用ThumbnailUtils类获取
实现简单,但2.2以前的版本不支持
3.调用jni文件,实现MediaMetadataRetriever类

实现复杂,但比较灵活,推荐使用


那么Android 中如何获取最近应用的缩略图,这块也有现成的函数,不过都被 @hide 掉了,所以需要利用java reflect 反射才能使用


核心代码如下:

package com.example.testondraw;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

import android.app.ActivityManager;
import android.graphics.Bitmap;
import android.util.Log;

/**
 * 调用隐藏方法的助手类
 */
public class HideExploder {
	static final String TAG = "HideExploder";
	private final static Object refLock = new Object();

	private static Method getTaskThumbnails = null;
	private static Field taskThumbnailsBitmap = null;

	@SuppressWarnings("rawtypes")
	public static void listAllObject(String classFullName) {
		try {
			Log.i(TAG, "listAllObject classFullName: " + classFullName);
			Class clazz = Class.forName(classFullName);

			// 反射属性字段
			Field[] fields = clazz.getDeclaredFields();

			// 反射方法字段
			Method[] methods = clazz.getDeclaredMethods();

			// 反射构造器
			Constructor[] constuctors = clazz.getDeclaredConstructors();

			Log.i(TAG, "FIELD========");
			for (Field f : fields) {
				Log.i(TAG, "TYPE: " + f.getType() + " NAME: " + f.getName());
			}

			Log.i(TAG, "METHOD========");
			for (Method m : methods) {
				Log.i(TAG, "METHOD NAME: " + m.getName());
			}

			Log.i(TAG, "CONSTUCTOR========");
			for (Constructor c : constuctors) {
				Log.i(TAG, "NAME:" + c.getName());

				Class[] clss = c.getParameterTypes();
				Object o = null;

				// 产生实例
				try {
					if (clss.length == 0)
						o = c.newInstance();
					else if (clss.length > 0) {
						// TODO
					}
					Log.i(TAG, "object: " + o);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	/**
	 * 调用逻辑
		 * TaskThumbnails o = am.getTaskThumbnails(id)
	 * Bitmap b = o.mainThumbnail;
		 * @param am ActivityManager 类实例
	 * @param id 标识值
	 * @return
	 */

	public static Bitmap getTaskThumbnailsBitmap(ActivityManager am, int id) {
		synchronized (refLock) {
			try {
				if (getTaskThumbnails == null) {
					getTaskThumbnails = am.getClass().getDeclaredMethod(
							"getTaskThumbnails", int.class);
				}
				if (getTaskThumbnails != null) {
					Object thumbnails = getTaskThumbnails.invoke(am,
							Integer.valueOf(id));
					if (thumbnails != null) {
						if (taskThumbnailsBitmap == null)
							taskThumbnailsBitmap = thumbnails.getClass()
									.getField("mainThumbnail");
						if (taskThumbnailsBitmap != null) {
							return (Bitmap) taskThumbnailsBitmap
									.get(thumbnails);
						}
					}
				}
			} catch (Exception e) {
				Log.w(TAG, "getTaskThumbnailsBitmap error:" + e);
				e.printStackTrace();
			}
		}
		return null;
	}
}

测试用例如下:


// 应用缩略图测试
	static final int MAX_RECENT_TASKS = 64;

	Bitmap loadThumbnail(int index) {
		ActivityManager am = (ActivityManager) this
				.getSystemService(Context.ACTIVITY_SERVICE);
		List recentTasks = am.getRecentTasks(
				MAX_RECENT_TASKS, ActivityManager.RECENT_IGNORE_UNAVAILABLE);
		int numTasks = recentTasks.size();

		if (index < numTasks) {
			final ActivityManager.RecentTaskInfo info = recentTasks.get(index);
			if (info != null) {
				Bitmap b = HideExploderX.getTaskThumbnailsBitmap(am,
						info.persistentId);
				return b;
			}
		}
		return null;
	}

调用 loadThumbnail(X) 【索引值为0就是上一次的缩略图】拿到Bitmap对象,利用 SurfaceView 方法画出来即可:

 

public void drawBitmap() {
		// 锁定画布,得到canvas
		if (mSurfaceHolder == null || this.mBitmap == null)
			return;

		Canvas canvas = mSurfaceHolder.lockCanvas();
		if (canvas == null) {
			return;
		}

		// 绘图
		Paint paint = new Paint();
		paint.setAntiAlias(true);
		paint.setColor(Color.BLUE);

		canvas.drawBitmap(this.mBitmap, 0, 0, paint);

		// 绘制后解锁,绘制后必须解锁才能显示
		mSurfaceHolder.unlockCanvasAndPost(canvas);
	}


注意点:

1、添加应用权限

    
    

   否则会报:

W/System.err( 3314): Caused by: java.lang.SecurityException: Permission Denial: getTaskThumbnails() from pid=3314, uid=10040 requires android.permission.READ_FRAME_BUFFER


2、有 eclipse 上调试运行时,即使加上权限了也还是会报上述错误,有两个方法解决,要么进行系统签名,要不放到linux上编译,利用platform 签名,Android.mk 如下:

LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)

LOCAL_MODULE_TAGS := optional

# Only compile source java files in this apk.
LOCAL_SRC_FILES := $(call all-java-files-under, src)

$(warning build apk)

LOCAL_PACKAGE_NAME := test

LOCAL_CERTIFICATE := platform

include $(BUILD_PACKAGE)

include $(call all-makefiles-under,$(LOCAL_PATH))


下一篇文章将针对其系统代码及原理分析清楚,用于新需求开发使用。


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