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【Android Developers Training】 72. 縮放一個

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注:本文翻譯自Google官方的Android Developers Training文檔,譯者技術一般,由于喜愛安卓而產生了翻譯的念頭,純屬個人興趣愛好。

原文鏈接: http://developer.android.com/training/animation/zoom.html


這節課將展示如何做一個觸摸縮放動畫,這個動畫非常常用,如在圖庫軟件中點擊照片的縮略圖,把照片放大到整個屏幕范圍:

Zoom動畫

如果你希望略過這部分內容直接看代碼樣例,可以直接 下載 樣例代碼,然后選擇淡入淡出動畫的例子。下面的文件是實現代碼:

  • src/TouchHighlightImageButton.java ?(一個簡單的輔助類,當圖片按鈕按下時,顯示一個藍色的觸摸點)
  • src/ZoomActivity.java
  • layout/activity_zoom.xml

一). 創建視圖

創建一個布局文件,包含了你希望縮放的大小視圖版本。下面的例子為一個可點擊的圖片縮略圖創建了一個 ImageButton ,以及展示放大圖片的 ImageView

      
        <
      
      
        FrameLayout 
      
      
        xmlns:android
      
      
        ="http://schemas.android.com/apk/res/android"
      
      
        

    android:id
      
      
        ="@+id/container"
      
      
        

    android:layout_width
      
      
        ="match_parent"
      
      
        

    android:layout_height
      
      
        ="match_parent"
      
      
        >
      
      
        <
      
      
        LinearLayout 
      
      
        android:layout_width
      
      
        ="match_parent"
      
      
        

        android:layout_height
      
      
        ="wrap_content"
      
      
        

        android:orientation
      
      
        ="vertical"
      
      
        

        android:padding
      
      
        ="16dp"
      
      
        >
      
      
        <
      
      
        ImageButton

            
      
      
        android:id
      
      
        ="@+id/thumb_button_1"
      
      
        

            android:layout_width
      
      
        ="100dp"
      
      
        

            android:layout_height
      
      
        ="75dp"
      
      
        

            android:layout_marginRight
      
      
        ="1dp"
      
      
        

            android:src
      
      
        ="@drawable/thumb1"
      
      
        

            android:scaleType
      
      
        ="centerCrop"
      
      
        

            android:contentDescription
      
      
        ="@string/description_image_1"
      
      
        />
      
      
        </
      
      
        LinearLayout
      
      
        >
      
      
        <!--
      
      
         This initially-hidden ImageView will hold the expanded/zoomed version of

         the images above. Without transformations applied, it takes up the entire

         screen. To achieve the "zoom" animation, this view's bounds are animated

         from the bounds of the thumbnail button above, to its final laid-out

         bounds.

         
      
      
        -->
      
      
        <
      
      
        ImageView

        
      
      
        android:id
      
      
        ="@+id/expanded_image"
      
      
        

        android:layout_width
      
      
        ="match_parent"
      
      
        

        android:layout_height
      
      
        ="match_parent"
      
      
        

        android:visibility
      
      
        ="invisible"
      
      
        

        android:contentDescription
      
      
        ="@string/description_zoom_touch_close"
      
      
        />
      
      
        </
      
      
        FrameLayout
      
      
        >
      
    

二). 設置縮放動畫

一旦你應用了你的布局后,配置時間句柄來激活縮放動畫。下面的例子給 ImageButton 添加了一個 View.OnClickListener 來,當用戶點擊按鈕時,執行縮放動畫:

      
        public
      
      
        class
      
       ZoomActivity 
      
        extends
      
      
         FragmentActivity {

    
      
      
        //
      
      
         Hold a reference to the current animator,

    
      
      
        //
      
      
         so that it can be canceled mid-way.
      
      
        private
      
      
         Animator mCurrentAnimator;



    
      
      
        //
      
      
         The system "short" animation time duration, in milliseconds. This

    
      
      
        //
      
      
         duration is ideal for subtle animations or animations that occur

    
      
      
        //
      
      
         very frequently.
      
      
        private
      
      
        int
      
      
         mShortAnimationDuration;



    @Override

    
      
      
        protected
      
      
        void
      
      
         onCreate(Bundle savedInstanceState) {

        
      
      
        super
      
      
        .onCreate(savedInstanceState);

        setContentView(R.layout.activity_zoom);



        
      
      
        //
      
      
         Hook up clicks on the thumbnail views.
      
      
        final
      
       View thumb1View =
      
         findViewById(R.id.thumb_button_1);

        thumb1View.setOnClickListener(
      
      
        new
      
      
         View.OnClickListener() {

            @Override

            
      
      
        public
      
      
        void
      
      
         onClick(View view) {

                zoomImageFromThumb(thumb1View, R.drawable.image1);

            }

        });



        
      
      
        //
      
      
         Retrieve and cache the system's default "short" animation time.
      
      

        mShortAnimationDuration =
      
         getResources().getInteger(

                android.R.integer.config_shortAnimTime);

    }

    ...

}
      
    

三). 縮放視圖

你現在需要再恰當地時間從標準尺寸變化到縮放后的視圖。一般而言,你需要將標準尺寸圖片的邊框擴大到更大的尺寸圖片的邊框。下面的方法展示了如何實現一個縮放動畫,它把一個圖片從縮略圖放大,具體是做了下面一些事情:

將高分辨率圖像指定到隱藏的“放大的” ImageView 。為了方便起見,下面的例子在UI資源加載了一個大圖片資源。你可能會希望在另一個線程進行加載來防止阻塞UI線程,之后再UI線程顯示位圖。在理想狀態下,位圖的大小應該不能超過屏幕的大小。

計算 ImageView 的起始和中止邊框大小。

在四個方向和尺寸屬性 X Y ,( SCALE_X ,和 SCALE_Y )同時執行動畫,從起始邊框一直到結束邊框。這四個動畫被添加到一個 AnimatorSet ,這樣他們能同時開始。

縮小時,執行同樣的動畫,但在用戶點擊已放大的圖像時,執行的是反向的動畫。你可以通過向 ImageView 添加 View.OnClickListener 來實現。當點擊時, ImageView 縮小為縮略圖的大小,并將它的可視性設置為 GONE 來隱藏它。

      
        private
      
      
        void
      
       zoomImageFromThumb(
      
        final
      
       View thumbView, 
      
        int
      
      
         imageResId) {

    
      
      
        //
      
      
         If there's an animation in progress, cancel it

    
      
      
        //
      
      
         immediately and proceed with this one.
      
      
        if
      
       (mCurrentAnimator != 
      
        null
      
      
        ) {

        mCurrentAnimator.cancel();

    }



    
      
      
        //
      
      
         Load the high-resolution "zoomed-in" image.
      
      
        final
      
       ImageView expandedImageView =
      
         (ImageView) findViewById(

            R.id.expanded_image);

    expandedImageView.setImageResource(imageResId);



    
      
      
        //
      
      
         Calculate the starting and ending bounds for the zoomed-in image.

    
      
      
        //
      
      
         This step involves lots of math. Yay, math.
      
      
        final
      
       Rect startBounds = 
      
        new
      
      
         Rect();

    
      
      
        final
      
       Rect finalBounds = 
      
        new
      
      
         Rect();

    
      
      
        final
      
       Point globalOffset = 
      
        new
      
      
         Point();



    
      
      
        //
      
      
         The start bounds are the global visible rectangle of the thumbnail,

    
      
      
        //
      
      
         and the final bounds are the global visible rectangle of the container

    
      
      
        //
      
      
         view. Also set the container view's offset as the origin for the

    
      
      
        //
      
      
         bounds, since that's the origin for the positioning animation

    
      
      
        //
      
      
         properties (X, Y).
      
      
            thumbView.getGlobalVisibleRect(startBounds);

    findViewById(R.id.container)

            .getGlobalVisibleRect(finalBounds, globalOffset);

    startBounds.offset(
      
      -globalOffset.x, -
      
        globalOffset.y);

    finalBounds.offset(
      
      -globalOffset.x, -
      
        globalOffset.y);



    
      
      
        //
      
      
         Adjust the start bounds to be the same aspect ratio as the final

    
      
      
        //
      
      
         bounds using the "center crop" technique. This prevents undesirable

    
      
      
        //
      
      
         stretching during the animation. Also calculate the start scaling

    
      
      
        //
      
      
         factor (the end scaling factor is always 1.0).
      
      
        float
      
      
         startScale;

    
      
      
        if
      
       ((
      
        float
      
      ) finalBounds.width() /
      
         finalBounds.height()

            
      
      > (
      
        float
      
      ) startBounds.width() /
      
         startBounds.height()) {

        
      
      
        //
      
      
         Extend start bounds horizontally
      
      

        startScale = (
      
        float
      
      ) startBounds.height() /
      
         finalBounds.height();

        
      
      
        float
      
       startWidth = startScale *
      
         finalBounds.width();

        
      
      
        float
      
       deltaWidth = (startWidth - startBounds.width()) / 2
      
        ;

        startBounds.left 
      
      -=
      
         deltaWidth;

        startBounds.right 
      
      +=
      
         deltaWidth;

    } 
      
      
        else
      
      
         {

        
      
      
        //
      
      
         Extend start bounds vertically
      
      

        startScale = (
      
        float
      
      ) startBounds.width() /
      
         finalBounds.width();

        
      
      
        float
      
       startHeight = startScale *
      
         finalBounds.height();

        
      
      
        float
      
       deltaHeight = (startHeight - startBounds.height()) / 2
      
        ;

        startBounds.top 
      
      -=
      
         deltaHeight;

        startBounds.bottom 
      
      +=
      
         deltaHeight;

    }



    
      
      
        //
      
      
         Hide the thumbnail and show the zoomed-in view. When the animation

    
      
      
        //
      
      
         begins, it will position the zoomed-in view in the place of the

    
      
      
        //
      
      
         thumbnail.
      
      
            thumbView.setAlpha(0f);

    expandedImageView.setVisibility(View.VISIBLE);



    
      
      
        //
      
      
         Set the pivot point for SCALE_X and SCALE_Y transformations

    
      
      
        //
      
      
         to the top-left corner of the zoomed-in view (the default

    
      
      
        //
      
      
         is the center of the view).
      
      
            expandedImageView.setPivotX(0f);

    expandedImageView.setPivotY(0f);



    
      
      
        //
      
      
         Construct and run the parallel animation of the four translation and

    
      
      
        //
      
      
         scale properties (X, Y, SCALE_X, and SCALE_Y).
      
      

    AnimatorSet set = 
      
        new
      
      
         AnimatorSet();

    set

            .play(ObjectAnimator.ofFloat(expandedImageView, View.X,

                    startBounds.left, finalBounds.left))

            .with(ObjectAnimator.ofFloat(expandedImageView, View.Y,

                    startBounds.top, finalBounds.top))

            .with(ObjectAnimator.ofFloat(expandedImageView, View.SCALE_X,

            startScale, 1f)).with(ObjectAnimator.ofFloat(expandedImageView,

                    View.SCALE_Y, startScale, 1f));

    set.setDuration(mShortAnimationDuration);

    set.setInterpolator(
      
      
        new
      
      
         DecelerateInterpolator());

    set.addListener(
      
      
        new
      
      
         AnimatorListenerAdapter() {

        @Override

        
      
      
        public
      
      
        void
      
      
         onAnimationEnd(Animator animation) {

            mCurrentAnimator 
      
      = 
      
        null
      
      
        ;

        }



        @Override

        
      
      
        public
      
      
        void
      
      
         onAnimationCancel(Animator animation) {

            mCurrentAnimator 
      
      = 
      
        null
      
      
        ;

        }

    });

    set.start();

    mCurrentAnimator 
      
      =
      
         set;



    
      
      
        //
      
      
         Upon clicking the zoomed-in image, it should zoom back down

    
      
      
        //
      
      
         to the original bounds and show the thumbnail instead of

    
      
      
        //
      
      
         the expanded image.
      
      
        final
      
      
        float
      
       startScaleFinal =
      
         startScale;

    expandedImageView.setOnClickListener(
      
      
        new
      
      
         View.OnClickListener() {

        @Override

        
      
      
        public
      
      
        void
      
      
         onClick(View view) {

            
      
      
        if
      
       (mCurrentAnimator != 
      
        null
      
      
        ) {

                mCurrentAnimator.cancel();

            }



            
      
      
        //
      
      
         Animate the four positioning/sizing properties in parallel,

            
      
      
        //
      
      
         back to their original values.
      
      

            AnimatorSet set = 
      
        new
      
      
         AnimatorSet();

            set.play(ObjectAnimator

                        .ofFloat(expandedImageView, View.X, startBounds.left))

                        .with(ObjectAnimator

                                .ofFloat(expandedImageView, 

                                        View.Y,startBounds.top))

                        .with(ObjectAnimator

                                .ofFloat(expandedImageView, 

                                        View.SCALE_X, startScaleFinal))

                        .with(ObjectAnimator

                                .ofFloat(expandedImageView, 

                                        View.SCALE_Y, startScaleFinal));

            set.setDuration(mShortAnimationDuration);

            set.setInterpolator(
      
      
        new
      
      
         DecelerateInterpolator());

            set.addListener(
      
      
        new
      
      
         AnimatorListenerAdapter() {

                @Override

                
      
      
        public
      
      
        void
      
      
         onAnimationEnd(Animator animation) {

                    thumbView.setAlpha(1f);

                    expandedImageView.setVisibility(View.GONE);

                    mCurrentAnimator 
      
      = 
      
        null
      
      
        ;

                }



                @Override

                
      
      
        public
      
      
        void
      
      
         onAnimationCancel(Animator animation) {

                    thumbView.setAlpha(1f);

                    expandedImageView.setVisibility(View.GONE);

                    mCurrentAnimator 
      
      = 
      
        null
      
      
        ;

                }

            });

            set.start();

            mCurrentAnimator 
      
      =
      
         set;

        }

    });

}
      
    

【Android Developers Training】 72. 縮放一個視圖


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