如何有效地编程？ 按下按钮时创建相应的活动

Question

I'm new to programming so I have a really easy question. Since I do not really know the terms I couldn't find any topic on my problem, so excuse me if this question has been asked before.

My problem is as follows: I'm running an app, created with Eclipse, on an Android machine. On the first screen I have just a list of buttons:

layout_main:

<Button
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_weight="1"
    android:text="@string/alpha"
    android:onClick="alpha" />

<Button
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_weight="1"
    android:text="@string/beta"
    android:onClick="beta"  />

If I press a button then the corresponding activity will start. I programmed the main activity as follow in order to do that:

main activity:

public void alpha(View view) {      
    Intent intent = new Intent(this, AlphaActivity.class);
     startActivity(intent); }

public void beta(View view) {       
    Intent intent = new Intent(this, BetaActivity.class);
     startActivity(intent); }

Since I have many buttons, I will have as many times the operation public void as seen above. Isn't there any way to program it more efficient? For example: Start new activity, if alpha was selected then start activity alpha, if beta was selected start activity beta, else do nothing.

Answer 1

You could apply the same listener to each button, not really sure if it's more efficient or even better style, but this will probably work. Something like:

public void buttonListen(View view)
{
     Class clas;
     int id = view.getId();
     switch(id)
     {
        case R.id.alpha:
            clas = AlphaActivity.class;
            break;
        case R.id.alpha:
            clas = BetaActivity.class;
            break;
        ...
        case R.id.zeta:
            clas = ZetaActivity.class;
            break;
      }
      startActivity(new Intent(this, clas));
}

and assign the corresponding id in the XML as the next answer states.

Answer 2

you can give every button an id like this :

<Button
    android:id="@+id/alpha"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_weight="1"
    android:text="@string/alpha"
    />

<Button
    android:id="@+id/beta"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_weight="1"
    android:text="@string/beta"
      />

then in the main activity you can findviewbyid() to find the two buttons and give buttons onclicklistener,then you implements the onclicklistener like this :

public void onClick(View v) {
    Intent i = new Intent();
    switch(v.getid()){
        case: R.id.alpha:
            i.setClass(context,AlphaActivity.class);
            break;
        case: R.id.beta:
            i.setClass(context,BetaActivity.class);
            break;
    }
    startActivity(i);
}

hope that helps.

Answer 3

There are many ways you could accomplish your goal.

Note: the best solution would be to add android:id to your layout file, but if for some reason you can't do that, you could use the button text.

A very simple (although not great) way to do it without changing your layout file much would be to look at the text on the button, if all buttons have unique text, and perform the action based on that.

public void onButtonClick(View view)
{
    //Cast the click View into a Button
    Button selectedButton = (Button) view;

    Intent intent = new Intent();

    String buttonText = selectedButton.getText().toString();

    if(buttonText.equals("beta"))
    {
        intent = new Intent(this, BetaActivity.class);
    }
    else if(buttonText.equals("alpha"))
    {
        intent = new Intent(this AlphaActivity.class);
    }

    startActivity(intent);
}

Make sure to set the onClick for each button in the layout file to call this method

android:onClick="onButtonClick"

Answer 4

There are many different ways to achieve this and make it simpler. Not a single method will be "the best". What you are doing is probably down the list of "what I would not do".

Don't assign things in XML, it's harder to work with, cannot be really changed at running time and make it less portable when you have to maintain a lot of different layouts. Instead…

This is just ONE way to do it:

Instead of defining the onClick method in the XML, do it programatically.

Add an android id to your Views:

<Button 
android:id="@+id/alpha_button"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:text="@string/alpha" />

(the same for all the other buttons)

Note: don't use fill_parent , use match_parent (the former is deprecated and both do the same).

The in your Activity onCreate() method, right before you setContentView(R.layout.your_above_layout_with_the_buttons);

You can obtain a reference to each button:

public void onCreate(Bundle savedInstanceState){
  super.onCreate(savedInstanceState);
  setContentView(R.layout.your_above_layout_with_the_buttons);
  final TextView alphaButton = (TextView) findViewById(R.id.alpha_button);
  //etc for the rest
  // now add click listeners:
  alphaButton.setOnClickListener(this);// more on this later
  betaButton.setOnClickListener(this);
  // etc.
}

Now your activity should be:

public class YourActivity extends Activity implements View.OnClickListener {

and somewhere in your activity you have to implement:

@Override
public void onClick(final View view) {
   // which button was clicked? Different ways to tell… a simple one:
   Intent intent;
   switch (v.getId()) {
      case R.id.alpha_button:
         intent = new Intent(this, AlphaActivity.class); 
         break;
      case R.id.beta_button:
         intent = new Intent(this, BetaActivity.class);
         break;
      //etc.
   }
   if (intent != null) {
      startActivity(intent);
   } 
}

Answer 5

For your specific situation, you could could change the way you handle the calls from your buttons, for example, you could give the buttons IDs and check the IDs of the buttons in a single method.

<Button
    android:id="@+id/alpha_button"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_weight="1"
    android:text="@string/alpha"
    android:onClick="onButtonClick" />

<Button
    android:id="@+id/beta_button"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:layout_weight="1"
    android:text="@string/beta"
    android:onClick="onButtonClick"  />



public void onButtonClick(View view) {
        Intent intent;
        switch (view.getId()) {
        case R.id.alpha_button:
            intent = new Intent(this, AlphaActivity.class);
            break;
        case R.id.beta_button:
            intent = new Intent(this, BetaActivity.class);
            break;
        default:
            return;
        }
        startActivity(intent);
    }

However, I would suggest that your current code is clear and concise so just leave it as it is. There are many ways to solve a problem, especially when it comes to designing software.

In general though, programming languages try to balance making code (and more importantly it's function or purpose) easy to read/understand while trying to keep the syntax as concise as possible. In time you will learn about the advantages and disadvantages of each language and it's syntax, some will be better at solving certain types of problem while being too verbose for solving others. For now just learn how Java works and try to understand why they have implemented each keyword and syntax element.