android：onClick =“ @ drawable /…不更新按钮onClick

Question

I'm attempting to update a button's image when it is clicked however the method I'm using within my XML file does not seem to be creating the desired effect (or any at all for that matter).

XML SNIPPET:

  <Button
      android:id="@+id/update_button"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_below="@+id/update_text"
      android:layout_centerHorizontal="true"
      android:layout_marginTop="90dp"
      android:background="@drawable/btn_update_inactive_hdpi" 
      android:onClick="@drawable/btn_update_active_hdpi"/>

Answer 1

In order to change the button's background when it is clicked you need to give it a selector.

btn_selector.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@drawable/btn_update_active_hdpi" android:state_pressed="true"></item>
    <item android:drawable="@drawable/btn_update_inactive_hdpi"></item>
</selector>

In your layout:

<Button
     android:id="@+id/update_button"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:layout_below="@+id/update_text"
     android:layout_centerHorizontal="true"
     android:layout_marginTop="90dp"
     android:background="@drawable/btn_selector"/>

Answer 2

android:onClick invokes a method. According to the docs:

android:onClick :

Name of the method in this View's context to invoke when the view is clicked. This name must correspond to a public method that takes exactly one parameter of type View. For instance, if you specify android:onClick="sayHello", you must declare a public void sayHello(View v) method of your context (typically, your Activity).

So, try to call a function when button clicks and in your Java code and change the drawable programatically inside that function. Something like:

In the xml file:

android:onClick="changeBackground"

In your code(activity where you set the view of this xml file), declare following dunction:

public void changeBackground(){
    Button button = (Button)findViewById(R.id.update_button);
    button .setBackgroundResource(R.drawable.btn_update_active_hdpi); 
}

PS: I haven't run the code, but I hope you get the sense of what I'm trying to say. Hope that helps

Answer 3

You can just use a selector to accomplish this. Create a new XML in your drawable folder and call it something like "btn_background.xml" and add the following:

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">

  <item android:drawable="@drawable/btn_update_active_hdpi" android:state_selected="true"></item>
  <item android:drawable="@drawable/btn_update_active_hdpi" android:state_pressed="true"></item>
  <item android:drawable="@drawable/btn_update_inactive_hdpi"></item>

</selector>

Then set your button's background

android:background="@drawable/btn_background"

The onClick property is used to assign a method in your Activity's java method to your button. (This is basically like doing the button.setOnClickListener().) If you want to set up an onClick listener, then you can do do the following:

In XML

android:onClick="NameOfMethod"

In Java Activity

public void NameOfMethod(View v){
  //Do Click Stuff Here
}