Android — Hiding Views

问题

Okay, so I've done some looking around and I see how you are SUPPOSED to do it, but for me, it is just not working.

I need to be able to set the alpha of a RelativeLayout both in XML and in code. For my XML, I have the following

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/player_controls"
    android:layout_height="match_parent"
    android:layout_width="match_parent"
    android:alpha="0.0">
    <RelativeLayout
        android:layout_height="match_parent"
        android:layout_width="match_parent"
        android:id="@+id/player_controls_touch_me"
        >
        </RelativeLayout>
</RelativeLayout>

I get the error: no resource identifier found for attribute 'alpha' in package 'android'

Also, based on the Android documentation, I should be able to call setAlpha(double) on any View object, but when I try to make that call on a RelativeLayout it tells me that this method is not defined for this object.

Why am I not able to control the alpha transparency for a RelativeLayout object in Android? Am i missing something? Thanks!

Update

Although using the visibility property works, it prevents me from be able to click on the ViewGroup. This is important for me because I am utilizing the OnTouchListener of the ViewGroup.

What I am trying to do is to have a layer with media controls, initially hidden. when the user taps anywere on the screen, I want the controls to fade in and when they tap the screen again I want the controls to fade out. I have this part already working. I am using a viewgroup that sits over-top my entire application with an OnTouchListener attached that can determine if it has or hasn't been touched. My problem is that after the animation runs to fade out the controls, they re-appear. If I use @Hydrangea suggestion, I can have it fade out and immediately made invisible. This gives me the desired effect, but then the ViewGroup is unclickable and the user cannot get the controls to come back (or go away, depending on what we decide to do first).

I hope this makes sense.

回答1:

You'll want to use a alpha animation to fade things in and out. This will maintain your touch events for your layouts. Here's an example

public class Main extends Activity {
/** Called when the activity is first created. */

private boolean mShowing = false;

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

    findViewById(R.id.textview).setOnClickListener(new OnClickListener(){

        @Override
        public void onClick(View arg0) {
            if(mShowing){
            Animation animation = new AlphaAnimation(1.0f, 0.0f);
            animation.setFillAfter(true);
            arg0.startAnimation(animation);
            } else {
                Animation animation = new AlphaAnimation(0.0f, 1.0f);
                animation.setFillAfter(true);
                arg0.startAnimation(animation);
            }

            mShowing = !mShowing;
        }

    });
}

}

Here's the accompanying xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:id="@+id/textview"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/hello"
    android:clickable="true"
    />
</LinearLayout>

回答2:

Unless you need levels of alpha between 0 and 1, I'd suggest, if you truly want to make this item invisible, to use setVisibility();

android:visibility="invisible"

I checked out the android:alpha line, and my ide doesn't find it either. I can't guess why, though... the documentation seems pretty clear.

回答3:

The alpha property is new in Android 3.0, and it's not the most efficient way to hide a view. Use View.setVisibility() or android:visibility to achieve what you want.

回答4:

You can set alpha by setting the (background) color i guess. Color values can be in the format of #aarrggbb (alpha, red, green, blue).

回答5:

You can add to the right answer the following option:

animation.setDuration(xxx);

To each animation instance. In this way your animation will look better.

回答6:

Based on your discription, you should be able to create a view that contains only the relative layout and have the onClickListener set to it. This way you can set the visibility of the relative layout to invisible, but still register a click.

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/clickable_layout"
    android:layout_height="match_parent"
    android:layout_width="match_parent" >
    <RelativeLayout
        android:id="@+id/player_controls"
        android:layout_height="match_parent"
        android:layout_width="match_parent" >
        <RelativeLayout
            android:layout_height="match_parent"
            android:layout_width="match_parent"
            android:id="@+id/player_controls_touch_me"
        >
        </RelativeLayout>
    </RelativeLayout>
</FrameLayout>

回答7:

Use onTouchEvent in Activity, and then you could get touch event to control to your RelativeLayout even if it is "invisible".

来源：https://stackoverflow.com/questions/5228768/android-hiding-views

标签

android

transparency

relativelayout

viewgroup