在Android中实现放大或缩小

放大和缩小动画分别用于在Android应用程序中放大和缩小视图的大小。开发人员通常使用这些类型的动画为应用程序提供动态特性。通过观看这些动画，用户还可以感觉到应用程序中正在发生的变化。

比例标记的XML属性

通过使用scale标签在XML文件中定义了“放大”和“缩小”动画的特性。

XML attribute	Description
android:duration	Used to define the duration of the animation in millisecond
android:fromXScale	Used to set initial size of the view in X-axis
android:fromYScale	Used to set initial size of the view in Y-axis
android:pivotX	To define the X coordinate of the point about which the object is being zoom in/out
android:pivotY	To define the Y coordinate of the point about which the object is being zoom in/out
android:toXScale	Used to set final size of the view in X-axis
android:toYScale	Used to set final size of the view in Y-axis

如何在Android中添加放大/缩小动画

下面的示例演示了对图像文件实施“放大”和“缩小”动画所涉及的步骤。使用ImageView将图像文件添加到活动中。

Note: Following steps are performed on Android Studio version 4.0

步骤1：建立新专案

1. 单击文件，然后单击新建=>新建项目。
2. 选择语言作为Kotlin。
3. 根据需要选择最小的SDK。

步骤2：修改activity_main.xml文件

以下是activity_main.xml文件的代码，用于在activity_main.xml中添加TextView，ImageView和两个Button。

步骤3：为图片的“放大”和“缩小”动画定义XML文件

通过右键单击res => New => Android Resource Directory在应用程序的res文件夹中创建一个新目录。选择资源类型作为动画，目录名称也应该是动画。在此目录中，创建2个动画资源文件，即zoom_in和zoom_out 。这两个文件是XML文件，其中包含动画的详细信息。以下是这两个文件的代码。

The android:fillAfter attribute under set tag is used to fix the final size of the image file until any other animation happens.

步骤4：修改MainActivity.kt文件

以下是MainActivity.kt文件的代码，可根据用户单击的按钮在ImageView小部件上加载和启动动画。

MainActivity.kt

package com.example.zomminout
   
import android.os.Bundle
import android.view.animation.AnimationUtils
import android.widget.Button
import android.widget.ImageView
import androidx.appcompat.app.AppCompatActivity
   
   
class MainActivity : AppCompatActivity() {
   
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
   
        // assigning id of the button
        // which zoom in the image
        val buttonZoomIn: Button = findViewById(R.id.zoomInButton)
   
        // assigning id of the button
        // which zoom out the image
        val buttonZoomOut: Button = findViewById(R.id.zoomOutButton)
   
        // assiging id of imageview on
        // which zoom in/out will be performed
        val image: ImageView = findViewById(R.id.imageView)
   
        // actions to be performed when
        // "Zoom In" button is clicked
        buttonZoomIn.setOnClickListener() {
   
            // loading the animation of
            // zoom_in.xml file into a variable
            val animZoomIn = AnimationUtils.loadAnimation(this,
                                                R.anim.zoom_in)
            // assigning that animation to
            // the image and start animation
            image.startAnimation(animZoomIn)
        }
   
        // actions to be performed when
        // "Zoom Out" button is clicked
        buttonZoomOut.setOnClickListener() {
   
            // loading the animation of
            // zoom_out.xml file into a variable
            val animZoomOut = AnimationUtils.loadAnimation(this,
                                                R.anim.zoom_out)
   
            // assigning that animation to
            // the image and start animation
            image.startAnimation(animZoomOut)
        }
    }
}

步骤5：修改字符串.xml文件

此文件中列出了活动中使用的所有字符串。

字符串.xml

    ZoomInOut
    Zoom In/Out in Android
    Zoom Out
    Zoom In

输出：在模拟器上运行

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