Android

//<activity ..
android:screenOrientation="landscape"
android:theme="@style/Theme.AppCompat.Light.NoActionBar"
tools:ignore="LockedOrientationActivity"
// ... >

https://stackoverflow.com/questions/21814825/you-need-to-use-a-theme-appcompat-theme-or-descendant-with-this-activity

0002

Button click event template/sample

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

    Button btnStart;
    Button btnExit;

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

        btnStart = findViewById(R.id.btnStart);
        btnExit = findViewById(R.id.btnExit);

        btnStart.setOnClickListener(this);
        btnExit.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        if(v == btnStart){
            Log.i("", "btnStart click");
        }else if(v == btnExit){
            Log.i("", "btnExit click");
        }
        /*
        switch(v.getId()){
        	case R.id.btnStart:
        		break;
        	case R.id.btnExit:
        		break;
        }
        */
    }
}

https://spicyboyd.blogspot.com/2018/04/apponclick5.html

Button should not assign before setContentView(R.layout.activity_main)

0003

Draw pixel art on background full screen

remember background.png put on drawable-nodpi folder

public class MenuBackground extends View {

    Bitmap bitmap;
    Paint paint = new Paint();
    int width;
    int height;

    public MenuBackground(Context context) {
        super(context);
        bitmap = BitmapFactory.decodeResource(this.getResources(), R.drawable.background);
        paint.setAntiAlias(false);
        paint.setDither(true);
        paint.setFilterBitmap(false);
        width = bitmap.getWidth();
        height = bitmap.getHeight();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        canvas.scale(getWidth() / (float)width , getHeight() / (float)height);
        canvas.drawBitmap(bitmap,0,0, paint);
        super.onDraw(canvas);
    }
}

https://stackoverflow.com/questions/46028774/disable-anti-aliasing-on-android-imageview

http://www.41post.com/4241/programming/android-disabling-anti-aliasing-for-pixel-art

0004

Use normal layout and custom View at same time

get layout class and use addView()

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    root = findViewById(R.id.root);
    root.addView(new MenuBackground(this));
}

0005

Use immersive sticky mode (no navigation bar, state bar)

@RequiresApi(api = Build.VERSION_CODES.KITKAT)
static void setImmersiveSticky(Activity activity){
    int option = View.SYSTEM_UI_FLAG_LOW_PROFILE
        | View.SYSTEM_UI_FLAG_FULLSCREEN
        | View.SYSTEM_UI_FLAG_LAYOUT_STABLE
        | View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY
        | View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION
        | View.SYSTEM_UI_FLAG_HIDE_NAVIGATION;
    activity.getWindow().getDecorView().setSystemUiVisibility(option);
}

https://developer.android.google.cn/training/system-ui/immersive?hl=zh-cn

https://www.jianshu.com/p/11a2b780fd9b

0006

Get width, height when using immersive sticky mode

DisplayMetrics displaymetrics = new DisplayMetrics();
activity.getWindowManager().getDefaultDisplay().getRealMetrics(displaymetrics);
screenWidth = displaymetrics.widthPixels;
screenHeight = displaymetrics.heightPixels;

0007

Open another activity

Intent intent = new Intent(this, GameActivity.class);
startActivity(intent);

0008

Navigation back button click

override this:

@Override
public void onBackPressed() {
    super.onBackPressed();
}

if you delete super.onBackPressed();,

You can't exit or back to upper activity by click navigation back button.

it is good and we can control the behavior of navigation back button.

Also, there are tutorial for press Back button two times and back :

https://www.youtube.com/watch?v=1Nmy88n7CZ8

0009

Navigation Home Press

No, you can't.

You can't override Home button.

https://stackoverflow.com/questions/4783960/call-method-when-home-button-pressed

https://stackoverflow.com/questions/8881951/detect-home-button-press-in-android/8883447#8883447

0010

Activity flow with surfaceview and navigation button press.

there show three flow line:

[1] : onStart -> onResume -> sufaceCreated -> surfaceChanged

[2] : onPause -> surfaceDestroyed

[3] : onBackPressed -> [2]

and flow event:

Start app -> [1]

[1] -> Press Home or Overview(the third/right one) -> [2]

[2] -> Back to app -> [1]

[1] -> press Back(the left one) -> [3]

You can control press back behaviour by override onBackPressed : 0008

https://source.android.com/devices/graphics/arch-sv-glsv

https://blog.csdn.net/ttmxh/article/details/7530531

0011

You can't restart thread, you should new a instance to use.

https://stackoverflow.com/questions/3826402/how-can-i-restart-a-thread-in-java-android-from-a-button/3826980

0012

Set Color relate to /res/value/color.xml

int color = ContextCompat.getColor(context, R.color.white);
paint.setColor(color);

https://stackoverflow.com/questions/12899428/how-to-set-paint-setcolorr-color-white

https://stackoverflow.com/questions/31590714/getcolorint-id-deprecated-on-android-6-0-marshmallow-api-23/31590927#31590927

0013

Change Bitmap Color

Paint p = new Paint();
ColorFilter filter = new LightingColorFilter(Color.RED, 0);
p.setColorFilter(filter);

https://gamedev.stackexchange.com/questions/5393/how-do-i-blend-a-bitmap-with-a-color

https://stackoverflow.com/questions/5699810/how-to-change-bitmap-image-color-in-android

On the other hand, you can change pixel by pixel

https://stackoverflow.com/questions/11449687/android-change-the-color-of-a-bitmap

https://stackoverflow.com/a/55204374/11693034

0014

Play Sound

MediaPlayer mediaPlayer;
mediaPlayer = MediaPlayer.create(<Context>, R.raw.xxx);

// Start
mediaPlayer.start();

// Stop (can not restart)
mediaPlayer.stop();

// Releases resources 
mediaPlayer.release();

// Reset (can restart) //
mediaPlayer.pause();
mediaPlayer.seekTo(0);

// Looping
mediaPlayer.setLooping(true);

https://developer.android.com/guide/topics/media/mediaplayer

0015

Change project name on Android Studio

Close Android Studio
Change project root directory name
Open Android Studio
Open the project (not from local history but by browsing to it)
Clean project

If your settings.gradle contains the below line, either delete it or update it to the new name.

rootProject.name = 'Your project name'

Rebuild Project

Click File -> Sync Project with Gradle Files

https://stackoverflow.com/questions/18276872/change-project-name-on-android-studio

0016

Play Video

videoView = findViewById(R.id.videoView);
String path = "android.resource://" + getPackageName() + "/" + R.raw.samplevideo;
Uri uri = Uri.parse(path);
videoView.setVideoURI(uri);

// Start 
videoView.start();

// Pause
videoView.pause();

// Reset (can restart) //
videoView.pause();
videoView.seekTo(0);

// I don't know how to use resume(), stop()

https://developer.android.com/reference/android/widget/VideoView.html

0017

Sensor Orientation

package com.example.motionsensorstest;

import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.os.Bundle;
import android.util.Log;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity implements SensorEventListener{

    SensorManager sensorManager;

    private Sensor accelerometer;
    private Sensor magnetometer;

    float[] accelerometerValues = new float[3];
    float[] magneticFieldValues = new float[3];

    float[] values = new float[3];

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

        sensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
        assert sensorManager != null;
        accelerometer = sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
        magnetometer = sensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);
    }

    protected void onResume() {
        super.onResume();
        sensorManager.registerListener(this, accelerometer, SensorManager.SENSOR_DELAY_UI);
        sensorManager.registerListener(this, magnetometer, SensorManager.SENSOR_DELAY_UI);
    }

    @Override
    protected void onPause() {
        super.onPause();
        sensorManager.unregisterListener(this);
    }

    public void onSensorChanged(SensorEvent sensorEvent) {
        switch (sensorEvent.sensor.getType()) {
            case Sensor.TYPE_MAGNETIC_FIELD:
                magneticFieldValues = sensorEvent.values;
                break;
            case Sensor.TYPE_ACCELEROMETER:
                accelerometerValues = sensorEvent.values;
                break;
        }
        updateOrientation();
        Log.i("","z: " + values[0] + "\tx: " + values[1] + "\ty: " + values[2]);
    }

    private  void updateOrientation() {
        float[] R = new float[9];
        SensorManager.getRotationMatrix(R, null, accelerometerValues, magneticFieldValues);
        SensorManager.getOrientation(R, values);

        values[0] = (float) Math.toDegrees(values[0]);
        values[1] = (float) Math.toDegrees(values[1]);
        values[2] = (float) Math.toDegrees(values[2]);
    }

    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {
        Log.i("", "onAccuracyChanged()");
    }
}

Package to be a class MyOrientationSensorManager :

package com.example.motionsensorstest;

import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.util.Log;

public class MyOrientationSensorManager implements SensorEventListener {

    public Context context;
    public SensorManager sensorManager;

    public Sensor accelerometer;
    public Sensor magnetometer;

    public float[] accelerometerValues = new float[3];
    public float[] magneticFieldValues = new float[3];

    public float[] values = new float[3];

    MyOrientationSensorManager(Context context){
        this.context = context;
        sensorManager = (SensorManager) context.getSystemService(Context.SENSOR_SERVICE);
        assert sensorManager != null;
        accelerometer = sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
        magnetometer = sensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);
    }

    public void reset(){
        sensorManager.registerListener(this, accelerometer, SensorManager.SENSOR_DELAY_UI);
        sensorManager.registerListener(this, magnetometer, SensorManager.SENSOR_DELAY_UI);
    }

    public void cancel(){
        sensorManager.unregisterListener(this);
    }

    public void onSensorChanged(SensorEvent sensorEvent) {
        switch (sensorEvent.sensor.getType()) {
            case Sensor.TYPE_MAGNETIC_FIELD:
                magneticFieldValues = sensorEvent.values;
                break;
            case Sensor.TYPE_ACCELEROMETER:
                accelerometerValues = sensorEvent.values;
                break;
        }
        updateOrientation();
        Log.i("","z: " + values[0] + "\tx: " + values[1] + "\ty: " + values[2]);
    }

    private  void updateOrientation() {
        float[] R = new float[9];
        SensorManager.getRotationMatrix(R, null, accelerometerValues, magneticFieldValues);
        SensorManager.getOrientation(R, values);

        values[0] = (float) Math.toDegrees(values[0]);
        values[1] = (float) Math.toDegrees(values[1]);
        values[2] = (float) Math.toDegrees(values[2]);
    }

    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {
        Log.i("", "onAccuracyChanged()");
    }

}

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