1.layout

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

    <ImageView
        android:layout_gravity="center_horizontal"
        android:layout_width="200dp"
        android:layout_height="200dp"
        android:id="@+id/imag" />

    <Button
        android:layout_marginTop="20sp"
        android:layout_gravity="center"
        android:id="@+id/next"
        android:text="下一張"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>
 

2.java

public class MainActivity extends AppCompatActivity {
    String[] images = null;
    AssetManager assets = null;
    int currentImg = 0;
    ImageView image;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        /*Bitmap b = new Bitmap();
        BitmapDrawable bd = new BitmapDrawable(b);
        Bitmap a = bd.getBitmap();*/

        image = (ImageView) findViewById(R.id.imag);
        try{
            assets = getAssets();
            images = assets.list("");//引數為資料夾的名字，空就是所有檔案.返回指定路徑下的所有檔案及目錄名string陣列
        } catch (Exception e){
            Log.i("mydate" , "錯誤1");
        }

        Button next = (Button) findViewById(R.id.next);
        next.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (currentImg >= images.length){
                    currentImg = 0;
                }
                //找下一張圖片
                while(!images[currentImg].endsWith(".png") && !images[currentImg].endsWith(".jpg") && !images[currentImg].endsWith(".gif")) {
                    currentImg ++; //過濾掉不為圖片的
                    if (currentImg >= images.length){
                        currentImg = 0;
                    }
                }
                InputStream assetFile = null;
                try{
                    //assets下的檔案只能讀(用open開啟inputsream)，不能寫
                    assetFile = assets.open(images[currentImg++]);
                } catch (Exception e){
                    Log.i("mydate" , "錯誤2");
                }

                //得到image的圖片
                BitmapDrawable bitmapDrawable = (BitmapDrawable) image.getDrawable();

                //先回收之前那張圖片
                if (bitmapDrawable != null && !bitmapDrawable.getBitmap().isRecycled()){
                    bitmapDrawable.getBitmap().recycle();
                }

                //設定新的圖片
                image.setImageBitmap(BitmapFactory.decodeStream(assetFile)); //將assets目錄下的圖片給image
            }
        });
 

3.assets中的檔案列表