是否有比调用onClickListener更好的方法来启动按钮单击上的新活动？

Question

Is there a better way of starting a new activity on a button click than using the onClick attribute to specify a callback method as in the example below?

--- xml ---

<Button
    android:id="@+id/button1"
    android:onClick="someMethod"
    android:text="@string/someString" />

--- java ---

public void someMethod(View view) {
    startActivity(new Intent(this, SomeActivity.class));
}

I would rather like to specify the name of the activity to be started than the name of a callback method. Like this:

<Button
    android:id="@+id/button1"
    android:onClick="SomeActivity"
    android:text="@string/someString" />

• I don't want to subclass the Button class.
• I don't want to specify the same callback method for all buttons and have a switch case in the callback method that starts the correct activity.
• Adding a custom xml attribute to the button that is specifying the activity to start (if it is possible?)

Answer 1

As a solution I would recommend the following. Please excuse the pseudo-like non-compiling (probably) code:

Button a = findViewById(R.id.button1);
Button b = findViewById(R.id.button2);

// Strings to be fed to the intent. You can use YourActivity.getClass() as well here
String mFirstTag  = "your.first.activity.class"
String mSecondTag = "your.second.activity.class"

// This is critical as it will be used by the listener
a.setTag(mFirstTag);
b.setTag(mSecondTag);

// Self explanatory
a.setOnClickListener(mClickListener);
b.setOnClickListener(mClickListener);


// This listener will grab the "tag" object from the clicked view.
// It will be the same tag which we previously set on those buttons.
private OnClickListener mClickListener = new OnClickListener() {
    @Override
    public void onClick(View v) {
        Intent i = new Intent(v.getTag()); // Maybe you'll need toString(), or a cast here
        startActivity(i);
    }
}

I hope you get the general idea.

Answer 2

This is what I came up with thanks to Jitsu and Mike M.

The Activity to be started when a button is pressed is specified using the android:tag xml attribute and the constructor will set the onClickListeners to all buttons in the View.

This way I don't have to:

1. Implement a onClick method for every button.
2. Implement one common onClick method with a switch statement that handles all buttons.
3. Subclass Button.
4. Create my own xml attribute.

--- xml ---

<RelativeLayout xmlns:tools="http://schemas.android.com/tools"
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/MainActivity"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.playground.MainActivity" >

        <Button
            android:id="@+id/button1"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:tag="showActivity"
            android:text="@string/somestring" />
</RelativeLayout>

--- java ---

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        connectButtonClickListeners(findViewById(R.id.MainActivity));
    }

    // Walk down the View tree starting with parent and connect an onClickListener to each Button.
    private void connectButtonClickListeners(View parent) {
        if (parent == null)
            return;

        LinkedList<View> list = new LinkedList<View>();
        list.add(parent);

        while (list.isEmpty() == false) {
            View v = list.pollFirst();
            if (v instanceof ViewGroup) {
                ViewGroup vg = (ViewGroup) v;
                for (int i = 0; i < vg.getChildCount(); i++)
                    list.add(vg.getChildAt(i));
            } else if (v instanceof Button) {
                Button b = (Button) v;
                b.setOnClickListener(new View.OnClickListener() {
                    public void onClick(View v) {
                        // TODO: Start the new Activity.
                        System.out.println("Clicked!" + v.getTag());
                    }
                });
            }
        }

Answer 3

It's simple. Subclass Button in a separate class file, MySpecialButton.java :

public class MySpecialButton extends Button {
  public MySpecialButton(Context context) {
     super(context);
     setupOnClickListener();
  }
  public MySpecialButton(Context context, AttributeSet attrs) {
     super(context);
     setupOnClickListener();
  }
  public MySpecialButton(Context context, AttributeSet attrs, int defStyle) {
     super(context);
     setupOnClickListener();
  }

  protected void setupOnClickListener() {
     setOnClickListener(new OnClickListener() {
          @Override
          public void onClick(View v) {
             startActivity(...);
          }
     });
  }
}

I haven't compiled this code, I wrote it in a hurry, but should work.

Then in your XML, instead of Button declare your view as com.yourpacket.yourappname.yourpackage.MySpecialButton .

EDIT: You do need to add some things in the code, but you should manage (context reference, import statements etc.).

Answer 4

I like this method. No switch statement required.

Each button gets the same onClickListener and a tag with a class name for the new activity:

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:onClick="startActivityForTag"
    android:tag=".HelloActivity"
    android:text="Say hello" >
</Button>

The click listener contructs a class from the view tag:

public void startActivityForTag(View v) {
    String name = v.getTag().toString();
    // if name is not fully-qualified, add the package name
    if (name.startsWith(".")) {
        name = getPackageName() + name;
    }
    try {
        startActivity(new Intent(this, Class.forName(name)));
    } catch (ClassNotFoundException e) { ; }
}