ImageView 四个指定图片的方法区别

今天在看人家一个继承ImagView的自定义控件，发现他覆写了这下面这四个方法。就在网上找了下这四个方法有啥区别，最后在Google Plus上找到了下面的解释。英文很差的我都看懂了，所以就不翻译了，直接搬运过来了。

ImageView has 4 APIs to specify the image. Which one to use? What is the difference?

1. setImageDrawable(Drawable drawable)
2. setImageBitmap(Bitmap bm)
3. setImageResource(int resId)
4. setImageURI(URI uri)

ImageView, by the name, is used to display an image. But what is a image? A Bitmap is-a image, not hard to understand and we use setImageBitmap for that purpose. However, internally, the ImageView has-a Drawable but not a Bitmap and that is what setImageDrawable for. When you call setImageBitmap, internally, first the bitmap will be wrapped to BitmapDrawable, which IS-A Drawable , and then call setImageDrawable.

Here is the code.

public void setImageBitmap(Bitmap bm) {
setImageDrawable(new BitmapDrawable(mContext.getResources(), bm));
}

So, what about the 3 and 4 API?

You should already know that that are bunches of ways to create a bitmap, from a file path, from the Uri, or from the resource file.

BitmapFactory.decodeFile(String pathName)
BitmapFactory.decodeStream(Inputstream)
BitmapFactory.decodeResource(Resource res, int id)
BitmapFactory.decodeByteArray(byte[] data)

Aware of this, it is easy to understand setImageResource/setImageUri is just same as setImageBitmap.

To sum up, setImageDrawable is the primitive function other APIs rely on. The other 3 are just helper methods making you write less code.

In addition, it is very important to keep in mind that ImageView actually has-a Drawable, which not necessarily to be a BitmapDrawable! You could set any Drawable to the Image view.

Besides setting the Drawable through Java API, you could also using XML attribution to set the source Drawable for ImageView. See example below. Note that the shape could be either an image file (.png,.jpg,.bmp) or xml file.

<ImageView
                           android:layout_width="match_parent"
                           android:layout_height="50dip"
                           android:src="@drawable/shape"/>

shape.xml

<shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="rectangle">
   <gradient android:startColor="#FFFF0000" android:endColor="#80FF00FF" android:angle="270"/>
   <padding android:left="7dp" android:top="7dp android:right="7dp" android:bottom="7dp" />
   <corners android:radius="8dp" />
</shape>

原文链接（要梯子）：
https://plus.google.com/+PierrChen/posts/VNAfFLDcKrw