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1． View 的getDrawingCache方法有时候需要将某个view的内容以图片的方式保存下来，感觉就和截图差不多，可以使用View 的getDrawingCache方法，返回一个Bitmap对象。
2． View的getDrawingCache的具体实现查看View的getDrawingCache（）方法
/** * <p>Calling this method is equivalent to calling <code>getDrawingCache(false)</code>.</p> * * @return A non-scaled bitmap representing this view or null if cache is disabled. * * @see #getDrawingCache(boolean) */ public Bitmap getDrawingCache() { return getDrawingCache(false); }
看代码继续调用了getDrawingCache(false)方法，继续查看getDrawingCache(false)方法。
/** * <p>Returns the bitmap in which this view drawing is cached. The returned bitmap * is null when caching is disabled. If caching is enabled and the cache is not ready, * this method will create it. Calling {@link #draw(android.graphics.Canvas)} will not * draw from the cache when the cache is enabled. To benefit from the cache, you must * request the drawing cache by calling this method and draw it on screen if the * returned bitmap is not null.</p> * * <p>Note about auto scaling in compatibility mode: When auto scaling is not enabled, * this method will create a bitmap of the same size as this view. Because this bitmap * will be drawn scaled by the parent ViewGroup, the result on screen might show * scaling artifacts. To avoid such artifacts, you should call this method by setting * the auto scaling to true. Doing so, however, will generate a bitmap of a different * size than the view. This implies that your application must be able to handle this * size.</p> * * @param autoScale Indicates whether the generated bitmap should be scaled based on * the current density of the screen when the application is in compatibility * mode. * * @return A bitmap representing this view or null if cache is disabled. * * @see #setDrawingCacheEnabled(boolean) * @see #isDrawingCacheEnabled() * @see #buildDrawingCache(boolean) * @see #destroyDrawingCache() */ public Bitmap getDrawingCache(boolean autoScale) { if ((mViewFlags & WILL_NOT_CACHE_DRAWING) == WILL_NOT_CACHE_DRAWING) { return null; } if ((mViewFlags & DRAWING_CACHE_ENABLED) == DRAWING_CACHE_ENABLED) { buildDrawingCache(autoScale); } return autoScale ? mDrawingCache : mUnscaledDrawingCache; }
查看getDrawingCache(false)方法，如果该视图的标志是WILL_NOT_CACHE_DEAWING（表示该view没有任何绘图缓存）则直接返回null，如果视图的标志是DRWING_CACHE_ENABLED（表示该view将自己的绘图缓存成一个bitmap），则调用buildDrawingCache(autoScale)方法。
因为传递过来的autoScale为false，则返回的Bitmap是mUnscaledDrawingCache。
查看buildDrawingCache(autoScale)方法：
/** * <p>Forces the drawing cache to be built if the drawing cache is invalid.</p> * * <p>If you call {@link #buildDrawingCache()} manually without calling * {@link #setDrawingCacheEnabled(boolean) setDrawingCacheEnabled(true)}, you * should cleanup the cache by calling {@link #destroyDrawingCache()} afterwards.</p> * * <p>Note about auto scaling in compatibility mode: When auto scaling is not enabled, * this method will create a bitmap of the same size as this view. Because this bitmap * will be drawn scaled by the parent ViewGroup, the result on screen might show * scaling artifacts. To avoid such artifacts, you should call this method by setting * the auto scaling to true. Doing so, however, will generate a bitmap of a different * size than the view. This implies that your application must be able to handle this * size.</p> * * <p>You should avoid calling this method when hardware acceleration is enabled. If * you do not need the drawing cache bitmap, calling this method will increase memory * usage and cause the view to be rendered in software once, thus negatively impacting * performance.</p> * * @see #getDrawingCache() * @see #destroyDrawingCache() */ public void buildDrawingCache(boolean autoScale) { if ((mPrivateFlags & PFLAG_DRAWING_CACHE_VALID) == 0 || (autoScale ? mDrawingCache == null : mUnscaledDrawingCache == null)) { if (Trace.isTagEnabled(Trace.TRACE_TAG_VIEW)) { Trace.traceBegin(Trace.TRACE_TAG_VIEW, "buildDrawingCache/SW Layer for " + getClass().getSimpleName()); } try { buildDrawingCacheImpl(autoScale); } finally { Trace.traceEnd(Trace.TRACE_TAG_VIEW); } } }
如果mPrivateFlags与PFLAG_DRAWING_CACHE_VALID与运算为0，或者mUnscaledDrawingCache为null，则调用buildDrawingCacheImpl(autoScale)方法。
查看buildDrawingCacheImpl(autoScale)方法,