Android Button setAlpha

Question

有一组按钮，我想得到结果：

当我点击其中一个时，我首先将它们分成两部分：点击的部分和其他部分。我正在尝试为它们设置不同的颜色或 alpha 值。

现在我使用setAlpha，但是当我将值从 0 更改为 255 时，它可以工作，但是当我将值从 255 更改为 0 时，它不工作。我不知道为什么。

也许在我调用方法Button.setAlpha()之后，我需要调用另一个方法？

我的代码：

public class MainActivity extends Activity {
 // button alpha value: minimize value
 public static int BUTTON_ALPHA_MIN = 0;

 // button alpha value: maximize value
 public static int BUTTON_ALPHA_MAX = 255;

 private LinearLayout centerRegion;
 private LinearLayout bottomRegion;

 private Button btnCheckIn;
 private Button btnReview;
 private Button btnMyCircles;
 private Button btnSettings;

 @Override
 public void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.main);

  // get all the widgets
  getAllWidgets();

  // set buttons click response function
  btnCheckIn.setOnClickListener(new OnClickListener() {
   public void onClick(View v) {
    centerRegion.setBackgroundColor(android.graphics.Color.RED);

    btnReview.getBackground().setAlpha(BUTTON_ALPHA_MIN);
    btnMyCircles.getBackground().setAlpha(BUTTON_ALPHA_MIN);
    btnSettings.getBackground().setAlpha(BUTTON_ALPHA_MIN);

    btnCheckIn.getBackground().setAlpha(BUTTON_ALPHA_MAX);
   }
  });

  btnReview.setOnClickListener(new OnClickListener() {

   public void onClick(View v) {
    centerRegion.setBackgroundColor(android.graphics.Color.BLUE);

    btnCheckIn.getBackground().setAlpha(BUTTON_ALPHA_MIN);
    btnMyCircles.getBackground().setAlpha(BUTTON_ALPHA_MIN);
    btnSettings.getBackground().setAlpha(BUTTON_ALPHA_MIN);

    btnReview.getBackground().setAlpha(BUTTON_ALPHA_MAX);
   }
  });

  btnMyCircles.setOnClickListener(new OnClickListener() {
   public void onClick(View v) {
    centerRegion.setBackgroundColor(android.graphics.Color.YELLOW);

    btnCheckIn.getBackground().setAlpha(BUTTON_ALPHA_MAX);
    btnReview.getBackground().setAlpha(BUTTON_ALPHA_MAX);
    btnSettings.getBackground().setAlpha(BUTTON_ALPHA_MAX);

    v.getBackground().setAlpha(BUTTON_ALPHA_MIN);
   }
  });

  btnSettings.setOnClickListener(new OnClickListener() {

   public void onClick(View v) {
    centerRegion.setBackgroundColor(android.graphics.Color.MAGENTA);

    btnCheckIn.getBackground().setAlpha(BUTTON_ALPHA_MAX);
    btnReview.getBackground().setAlpha(BUTTON_ALPHA_MAX);
    btnMyCircles.getBackground().setAlpha(BUTTON_ALPHA_MAX);

    v.getBackground().setAlpha(BUTTON_ALPHA_MIN);
   }
  });
 }

 /**
  * get all the widgets
  */
 public void getAllWidgets() {
  this.centerRegion = (LinearLayout) this.findViewById(R.id.center_region);
  this.bottomRegion = (LinearLayout) this.findViewById(R.id.bottom_region);

  this.btnCheckIn = (Button) this.findViewById(R.id.button_check_in);
  this.btnReview = (Button) this.findViewById(R.id.button_review);
  this.btnMyCircles = (Button) this.findViewById(R.id.button_my_circles);
  this.btnSettings = (Button) this.findViewById(R.id.button_setting);
 }
}

Answer 1

使用 AlphaAnimation 应该可以；在我的设备上验证。

public class Test extends Activity implements OnClickListener {

    private AlphaAnimation alphaDown;
    private AlphaAnimation alphaUp;
    private Button b1;
    private Button b2;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        LinearLayout ll = (LinearLayout) findViewById(R.id.linear_layout);

        b1 = new Button(this);
        b1.setText("Button 1");
        b1.setOnClickListener(this);
        ll.addView(b1);

        b2 = new Button(this);
        b2.setText("Button 2");
        b2.setOnClickListener(this);
        ll.addView(b2);

        alphaDown = new AlphaAnimation(1.0f, 0.3f);
        alphaUp = new AlphaAnimation(0.3f, 1.0f);
        alphaDown.setDuration(1000);
        alphaUp.setDuration(1000);
        alphaDown.setFillAfter(true);
        alphaUp.setFillAfter(true);
    }

    public void onClick(View v) {
        if (v == b1) {
            b1.startAnimation(alphaUp);
            b2.startAnimation(alphaDown);
        } else {
            b1.startAnimation(alphaDown);
            b2.startAnimation(alphaUp);
        }
    }
}

关键是调用setFillAfter(true)，这样alpha 变化就会持续存在。

Answer 2

感谢您的提问和回答。这真的帮助了我。

对于我的解决方案，我需要在没有看到任何动画效果的情况下设置按钮的 alpha，但 button.setAlpha(x) 偶尔会失败。改用动画就可以了，但我必须将持续时间设置为零才能获得自动效果。

alphaDown = new AlphaAnimation(1.0f, 0.3f);
alphaUp = new AlphaAnimation(0.3f, 1.0f);
alphaDown.setDuration(0);
alphaUp.setDuration(0);
alphaDown.setFillAfter(true);
alphaUp.setFillAfter(true);

我将它用于媒体应用程序中的播放器控件，所以我有这样的东西：

    boolean bInitPrevEnabled = m_btPrev.isEnabled();
    boolean bInitNextEnabled = m_btNext.isEnabled();
    boolean bInitPlayEnabled = m_btPlay.isEnabled();

    m_btPrev.setEnabled(true);
    m_btNext.setEnabled(true);
    m_btPlay.setEnabled(true);

    // Process enabling of the specific buttons depending on the state

    if (bInitPrevEnabled != m_btPrev.isEnabled())
            m_btPrev.startAnimation((m_btPrev.isEnabled()) ? alphaUp : alphaDown);

    if (bInitNextEnabled != m_btNext.isEnabled())
            m_btNext.startAnimation((m_btNext.isEnabled()) ? alphaUp : alphaDown);

    if (bInitPlayEnabled != m_btPlay.isEnabled())
            m_btPlay.startAnimation((m_btPlay.isEnabled()) ? alphaUp : alphaDown);

Answer 3

Button btn;

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);   
    setContentView(R.layout.main);  
    btn = (Button) findViewById(R.id.main_btn);  
    Drawable d = getResources().getDrawable(R.drawable.imagen);  
    d.setAlpha(60);  
    btn.setBackgroundDrawable(d);  
}

这对我有用:)

Answer 4

public void setAlpha (int alpha) - 已弃用

public void setAlpha (float alpha) (0f