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Android Handler

The concept here is android handlers. Feel free to add more handler examples.

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  1. Android Handler – Update ProgressBar

    Android Handler and ProgressBar Update Tutorial and Examples

    In this tutorial we want to see how to post updates from a background thread to the user interface thread using a Handler.

    We click a button and simulate doing heavy work in the background. Meanwhile we are able to update our progressbar as the work continues.

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    Well we have a video tutorial as an alternative to this. If you prefer tutorials like this one then it would be good you subscribe to our YouTube channel. Basically we have a TV for programming where do daily tutorials especially android.

    (a). MainActivity.java

    This is the main activity. We derive from the AppCompatActivity. One of the imports we add is the Handler from the android.os package.

    ...
    import android.os.Handler;
    ...

    We will maintain three instance fields:

    1. Handler – a class defined in the android.os package through which we can send and process Message and Runnable objects associated with a thread’s MessageQueue.
    2. ProgressBar – a widget that allows us to show progress.
    3. Button – an action button.

    Here’s the full code:

    package info.camposha.mrhandler;
    
    import android.os.Bundle;
    import android.os.Handler;
    import android.support.v7.app.AppCompatActivity;
    import android.view.View;
    import android.widget.Button;
    import android.widget.ProgressBar;
    
    public class MainActivity extends AppCompatActivity {
    
        private Handler mHandler;
        private ProgressBar mProgressBar;
        private Button mStartButton;
    
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            mHandler = new Handler();
            mProgressBar = findViewById(R.id.mProgressBar);
            mStartButton = findViewById(R.id.startBtn);
            mStartButton.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View view) {
                    performStuff();
                }
            });
        }
        private void performStuff() {
            //Simulate Heavy task in background thread
            new Thread(new Runnable() {
                @Override
                public void run() {
                    for (int i = 0; i <= 30; i++) {
                        final int currentProgressCount = i;
                        try {
                            Thread.sleep(500);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
    
                    //Post updates to the User Interface
                        mHandler.post(new Runnable() {
                            @Override
                            public void run() {
                                mProgressBar.setProgress(currentProgressCount);
                            }
                        });
                    }
                }
            }).start();
        }
    }

    (b). activity_main.xml

    This is the main activity layout. At the root we have a LinearLayout. This element allows us to arrange it’s children linearly either horizontally or vertically. We also have TextView to display the header text of our app. Also we have a progressbar to display progress. We have also a button that when clicked will start the thread to perform our work in the background thread.

    <?xml version="1.0" encoding="utf-8"?>
    <LinearLayout 
        android_layout_width="match_parent"
        android_layout_height="match_parent"
        
        android_gravity="center"
        android_orientation="vertical"
        tools_context=".MainActivity">
    
        <TextView
            android_id="@+id/headerLabel"
            android_layout_width="wrap_content"
            android_layout_height="wrap_content"
            android_layout_alignParentTop="true"
            android_layout_centerHorizontal="true"
            android_fontFamily="casual"
            android_text="Handler ProgressBar"
            android_textAllCaps="true"
            android_textSize="24sp"
            android_textStyle="bold" />
    
        <ProgressBar
            android_id="@+id/mProgressBar"
            style="?android:attr/progressBarStyleHorizontal"
            android_layout_width="match_parent"
            android_layout_height="wrap_content"
            android_layout_margin="10dp"
            android_indeterminate="false"
            android_max="10" />
    
        <Button
            android_id="@+id/startBtn"
            android_layout_width="wrap_content"
            android_layout_height="wrap_content"
            android_text="Start" />
    </LinearLayout>



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