如何在Android中循环运行

Question

I'm doing an application in which I have to show a sequence of pictures: The sequence is the follow:

1. A red X has to be shown for more or less 400 milliseconds;
2. An image called "Screenshot" has to be shown for more or less 500 milliseconds;
3. An image called "Noise" has to be shown for more or less 50 milliseconds;
4. The "Noise" image disappear to make space for an EditText .

The EditText is used to get the user data.

Here is my code:

public class Step1Training extends Activity {

    ImageFragment myImageFragment;
    InputFragment myInputFragment;
    Drawable cross;
    ImageView myImageView;
    EditText myEditText;
    int i, length;
    String rating;
    Handler handler;
    boolean continueTask;
    int[] screenshots = {
           R.drawable.googleplaybooks2,
           R.drawable.aldiko1,
           R.drawable.chaton2,
           R.drawable.cinetrailer1,
           R.drawable.fanpage1
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.step1_training);

        handler = new Handler();
        i = 0;
        length = screenshots.length;

        initUI();

        startThread();
    }

    private void initUI(){
        myImageFragment = (ImageFragment)getFragmentManager().findFragmentById(R.id.imageFragment);
        myInputFragment = (InputFragment)getFragmentManager().findFragmentById(R.id.inputFragment);

        myImageView = (ImageView)myImageFragment.getView().findViewById(R.id.screenshotImageView);
        myImageView.setImageResource(R.drawable.cross300x300);

        myEditText = (EditText)myInputFragment.getView().findViewById(R.id.ratingEditText);     
        myEditText.setVisibility(View.GONE);
    }

    private void startThread(){

        while(i<length){
            handler.postDelayed(new TaskScreenshot(i), 250);
            handler.postDelayed(new TaskNoise(), 750);
            handler.postDelayed(new TaskEditText(), 1000);

            myEditText.setOnKeyListener(new View.OnKeyListener(){
                public boolean onKey(View v, int keyCode, KeyEvent event) {
                    if((keyCode == KeyEvent.KEYCODE_ENTER)) {
                        if(myEditText.getText().toString().equals("")){
                            Toast.makeText(getApplicationContext(), "Inserire un numero da 1 a 9", Toast.LENGTH_SHORT).show();
                            return false;
                        } else if (Integer.parseInt(myEditText.getText().toString()) >= 1 &&
                                Integer.parseInt(myEditText.getText().toString()) <= 9){
                            return true;
                        }
                    }
                    return false;
                }
            });
            System.out.println(i);
            i++;
        }   
    }

    @Override
    public void onBackPressed() {
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("Attenzione")
        .setMessage("Sei sicuro/a di voler uscire dall'applicazione?\n" +
                "Confermando uscirai dall'applicazione e perderai \n" +
                "tutti i dati raccolti finora.")
        .setCancelable(false)
        .setNegativeButton("No",new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int id) {
                dialog.cancel();
            }
        })
        .setPositiveButton("Si", new DialogInterface.OnClickListener()
        {
            @Override
            public void onClick(DialogInterface dialog, int whichButton)
            {
                Intent intent = new Intent(Intent.ACTION_MAIN);
                intent.addCategory(Intent.CATEGORY_HOME);
                intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                startActivity(intent);
            }
        });
        AlertDialog alert = builder.create();
        alert.show();
    }

    class TaskScreenshot implements Runnable{

        int j;

        public TaskScreenshot(int _i){
            this.j = _i;
        }

        @Override
        public void run() {
            System.out.println("Screenshot");
            myEditText.setVisibility(View.GONE);
            myImageFragment.getView().setVisibility(View.VISIBLE);
            myImageView.setImageResource(screenshots[j]);
            myImageView.getLayoutParams().width = LayoutParams.MATCH_PARENT;
            myImageView.getLayoutParams().height = LayoutParams.MATCH_PARENT;
        }
    }

    class TaskNoise implements Runnable{

        @Override
        public void run() {
            System.out.println("Noise");
            myImageView.setImageResource(R.drawable.noise);
            myImageView.getLayoutParams().width = LayoutParams.MATCH_PARENT;
            myImageView.getLayoutParams().height = LayoutParams.MATCH_PARENT;
        }
    }

    class TaskEditText implements Runnable{

        @Override
        public void run() {
            System.out.println("EditText");
            myEditText.setVisibility(View.VISIBLE);
            myImageFragment.getView().setVisibility(View.GONE);
        }
    }
}

When I run this activity, it shows the red X , the last screenshot of the array and the Noise image. The Logcat shows this:

0
1
2
3
4
Screenshot
Screenshot
Screenshot
Screenshot
Screenshot
Noise
Noise
Noise
Noise
Noise
EditText
EditText
EditText
EditText
EditText

What am I doing wrong in this loop? And, how can I stop the loop until the user put the data?

UPDATE 1:

I've changed the code as the user Groco have suggested:

private void startThread(final int i){



    if(i < length){

                handler.postDelayed(new TaskScreenshot(i), 250);
                handler.postDelayed(new TaskNoise(), 750);
                handler.postDelayed(new TaskEditText(), 1000);

                myEditText.setOnKeyListener(new View.OnKeyListener(){
                    public boolean onKey(View v, int keyCode, KeyEvent event) {
                        if((keyCode == KeyEvent.KEYCODE_ENTER)) {
                            if(myEditText.getText().toString().equals("")){
                                Toast.makeText(getApplicationContext(), "Inserire un numero da 1 a 9", Toast.LENGTH_SHORT).show();
                                return false;
                            } else if (Integer.parseInt(myEditText.getText().toString()) >= 1 &&
                                    Integer.parseInt(myEditText.getText().toString()) <= 9){
                                System.out.println(i);
                                startThread(i+1);
                                return true;
                            }
                        }
                        return false;
                    }
                });

            }   
        }

But when I run it, the application shows the 1°, 3° and 5° screenshot (index 0, 2, 4) and not all of them. Am I doing something wrong with the index?

Answer 1

Use the result of the user interaction to relaunch a cycle:

 private void startThread(int i){
        if (i<length){

            handler.postDelayed(new TaskScreenshot(i), 250);
            handler.postDelayed(new TaskNoise(), 750);
            handler.postDelayed(new TaskEditText(), 1000);

            myEditText.setOnKeyListener(new View.OnKeyListener(){
                public boolean onKey(View v, int keyCode, KeyEvent event) {
                    if((keyCode == KeyEvent.KEYCODE_ENTER)) {
                        if(myEditText.getText().toString().equals("")){
                            Toast.makeText(getApplicationContext(), "Inserire un numero da 1 a 9", Toast.LENGTH_SHORT).show();
                            return false;
                        } else if (Integer.parseInt(myEditText.getText().toString()) >= 1 &&
                                Integer.parseInt(myEditText.getText().toString()) <= 9){
                            System.out.println(i);
                            i++;
                            startThread(i);
                        }
                    }
                    return false;
                }
            });

        }
        return false;
}

Answer 2

try this:

    private void startThread(){

        while(i<length){
            handler.postDelayed(new TaskScreenshot(i), 250);

            myEditText.setOnKeyListener(new View.OnKeyListener(){
                ....
            }
    }

    class TaskScreenshot implements Runnable{

        int j;

        public TaskScreenshot(int _i){
            this.j = _i;
        }

        @Override
        public void run() {
            ...
            handler.postDelayed(new TaskNoise(), 500);
        }
    }

    class TaskNoise implements Runnable{

        @Override
        public void run() {
            ...
            handler.postDelayed(new TaskEditText(), 250);
        }
    }

    class TaskEditText implements Runnable{

        @Override
        public void run() {
            ...
            myImageFragment.getView().setVisibility(View.GONE);
        }
    }

hope this will help

Regarding the second question, why do not start the loop after user enters data ?

Answer 3

Your loop schedules a bunch of events to happen all at the same time. You may want to include i in the delay calculation, ie something like :

handler.postDelayed(new TaskScreenshot(i), i*1500 + 250);
...

A better approach may be for each stage to schedule the next. I also note that your startThread() function does not actually start a new thread. Everything happens on the main thread, which is right and proper.