Java 更改按钮上的图像单击

我是android开发的新手，在这里我尝试通过点击按钮来改变图像，我使用动画方法来淡出其中一幅图像并获得效果。第一次点击按钮是淡出图像，但第二次点击这个按钮时，它不会给出任何结果图像不会淡出

给我任何可能的解决办法。谢谢

.java文件

package e.nani.bestimage;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ImageView;

public class MainActivity extends AppCompatActivity {

public void change(View view) {
    int flag=0;
    ImageView img1 = (ImageView) findViewById(R.id.single);
    ImageView img2 = (ImageView) findViewById(R.id.withands);
    switch(flag){

    case 0:img1.animate().alpha(0f).setDuration(2000);
                img2.animate().alpha(1f).setDuration(2000);
                flag=1;
                break;
        case 1:    img1.animate().alpha(1f).setDuration(2000);
            img2.animate().alpha(0f).setDuration(2000);
            flag=0;
            break;
    }
    }
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ImageView img1=(ImageView) findViewById(R.id.single);
    ImageView img2=(ImageView) findViewById(R.id.withands);
    img1.animate().alpha(1f).setDuration(2000);
    img2.animate().alpha(0f).setDuration(2);

}

}

xml文件

<?xml version="1.0" encoding="utf-8"?>
<android.widget.RelativeLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@android:color/holo_purple"
tools:context=".MainActivity">

<ImageButton
    android:id="@+id/single"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:scaleType="centerCrop"
    app:srcCompat="@drawable/imgthree" />

<ImageView
    android:id="@+id/withands"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_weight="1"
    android:clickable="true"
    app:srcCompat="@drawable/imgsix" />

<Button
    android:id="@+id/button"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_centerHorizontal="true"
    android:layout_marginBottom="98dp"
    android:alpha="0.7"
    android:background="@android:color/background_dark"
    android:onClick="change"
    android:text="find out the person"
    android:textColor="@android:color/holo_blue_bright" />
    </android.widget.RelativeLayout>

---

只要调用change方法，它就会将标志设置为0。试试这个：

public class MainActivity extends AppCompatActivity {

int flag;
public void change(View view) {

ImageView img1 = (ImageView) findViewById(R.id.single);
ImageView img2 = (ImageView) findViewById(R.id.withands);
switch(flag){

  case 0:
            img1.animate().alpha(0f).setDuration(2000);
            img2.animate().alpha(1f).setDuration(2000);
            flag=1;
            break;
    case 1:   
        img1.animate().alpha(1f).setDuration(2000);
        img2.animate().alpha(0f).setDuration(2000);
        flag=0;
        break;
  }
}
 @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_main);
   flag = 0;
   ImageView img1=(ImageView) findViewById(R.id.single);
   ImageView img2=(ImageView) findViewById(R.id.withands);
   img1.animate().alpha(1f).setDuration(2000);
   img2.animate().alpha(0f).setDuration(2);

 }

 }