interface design:
Related classes: Activity , Fragment , View , ViewGroup , Layout .
view:
简单控件：Button、ImageButton、ToggleButton、TextView、EditText、RadioButton、CheckBox、ImageView、ProgressBar、SeekBar、RatingBar等。
Advanced controls: AutoCompleteTextView , Spinner , ListView , GridView , Gallery , etc.
View Group ( ViewGroup ): A complex view composed of multiple views, a subclass of View , and a parent class for advanced controls and layouts.
Interface construction:
Design tool: WYSIWYG visual interface design tool.
Control time processing:
Event source: each control.
Events: EG : KeyEvent , MotionEvent (encapsulated into a class) Special: Button click event is not encapsulated
Event handler: implement the XXXListenter interface --> event listener.
Listener:
Activity as event listener:
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate (savedInstanceState);
setContentView(R.layout.activity_main);
// Get the OK button object by id
Button btnOK = (Button) findViewById(R.id.button);
// register event listener
btnOK.setOnClickListener(this);
}
/*
* Implement the View.OnClickListener interface method
*/
@Override
public void onClick(View view) {
TextView text = (TextView) findViewById(R.id.textView);
text.setText("HelloWorld");
}
}
Inner class event listener:
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate (savedInstanceState);
setContentView(R.layout.activity_main);
// Get the OK button object by id
Button btnOK = (Button) findViewById(R.id.button);
// register event listener
btnOK.setOnClickListener(new ButtonOKOnClickListener());
}
class ButtonOKOnClickListener implements View.OnClickListener {
/*
* Implement the View.OnClickListener interface method
*/
@Override
public void onClick(View view) {
TextView text = (TextView) findViewById(R.id.textView);
text.setText("HelloWorld");
}
}
}
Anonymous inner class event listener:
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate (savedInstanceState);
setContentView(R.layout.activity_main);
// Get the OK button object by id
Button btnOK = (Button) findViewById(R.id.button);
// register event listener
btnOK.setOnClickListener(new View.OnClickListener() {
/*
* Implement the View.OnClickListener interface method
*/
@Override
public void onClick(View v) {
TextView text = (TextView) findViewById(R.id.textView);
text.setText("HelloWorld");
}
});
}
}
Handling of screen events: (touch events && keyboard events)
Touch event: // Override the method of the activity public boolean onTouchEvent(MotionEvent event)
// Display the current action and position on the screen
public class MainActivity extends AppCompatActivity {
// Two TextViews are displayed respectively: action, position
private TextView mAction;
private TextView mPostion;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate (savedInstanceState);
setContentView(R.layout.activity_main);
mAction = (TextView) findViewById(R.id.action);
mPostion = (TextView) findViewById (R.id.postion);
}
// This method ( onTouchEvent() ) must be overridden
@Override
public boolean onTouchEvent(MotionEvent event) {
int action = event.getAction();// Action Action is constant
switch (action) {
case MotionEvent.ACTION_UP:
mAction.setText(" Finger up ");
break;
case MotionEvent.ACTION_DOWN:
mAction.setText(" Finger press ");
break;
case MotionEvent.ACTION_MOVE:
mAction.setText(" Finger move ");
}
// Get X- axis, Y- axis coordinates
float X = event.getX();
float Y = event.getY();
mPostion.setText("位置 = (" + X + "," + Y + ")");
return true; // return true to execute this method, otherwise false
}
}
Keyboard events:
//keyCode is the code of the key; KeyEvent is the keyboard event
Boolean onKeyUp (int keyCode ,KeyEvent event)
Boolean onKeyDown (int keyCode ,KeyEvent event)
Boolean onKeyLongPress (int keyCode ,KeyEvent event)
The combination of the transparency of the picture and the sound button Demo :
public class MainActivity extends AppCompatActivity {
private static final String TAG = "keyeventsample";
private ImageView mImage;
private TextView mAlphavalueText;
private int mAlphavalue; // Global variable, current image transparency: ( 0,255 )
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate (savedInstanceState);
setContentView(R.layout.activity_main);
mImage = (ImageView) findViewById(R.id.image);
mAlphavalueText = (TextView) findViewById(R.id.alphavalue);
mAlphavalue = 100; // The initial value of transparency is 100
mImage.setImageAlpha(mAlphavalue); // Set the image transparency
mAlphavalueText.setText("Alpha = " + mAlphavalue * 100 / 255 + "%");
}
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
// listen for all keyboard events
switch (keyCode) {
case KeyEvent.KEYCODE_VOLUME_UP:// Amplify sound key
mAlphavalue += 20;
break;
case KeyEvent.KEYCODE_VOLUME_DOWN:// scale down the sound key
mAlphavalue -= 20;
break;
}
if (mAlphavalue >= 255) {
mAlphavalue = 255;
}
if (mAlphavalue <= 0) {
mAlphavalue = 0;
}
mImage.setImageAlpha (mAlphavalue);
mAlphavalueText.setText("Alpha = " + mAlphavalue * 100 / 255 + "%");
return super.onKeyDown(keyCode, event);
}
}
Purpose: Make reasonable use of screen space and adapt to different screens
The layout class is a container that inherits the ViewGroup class
Six basic layout classes:
FrameLayout/LinearLayout/AbsoluteLayout/RelativeLayout/TableLayout/GridLayout
FrameLayout : ( FrameLayout , frame layout) is not used very often, its subclasses are often used
子类：TextSwitcher/ImageSwitcher/DatePicker/ScrollView/TabHost
Linear Layout: The Most Common Layout
android:orientation=”vertical/horizontal” ( vertical arrangement, horizontal arrangement )
android:layout_weight=”X”
Relative layout: (layout code omitted)
padding : (padding)
margin : (outer margin)
Grid layout implementation:
<GridLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:columnCount="4"
android:orientation="horizontal"
android:rowCount="5">
<Button
android:id="@+id/zero"
android:layout_columnSpan="2"
android:layout_gravity="fill"
android:text="0" />
<Button
android:id="@+id/point"
android:text="." />
<Button
android:id="@+id/plus"
android:layout_gravity="fill"
android:layout_rowSpan="2"
android:text="+" />
<Button
android:id="@+id/equal"
android:layout_columnSpan="3"
android:layout_gravity="fill"
android:text="=" />
</GridLayout>
Nesting of layouts:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:text="@string/title"
android:textSize="20sp" />
<include
android:id="@+id/include01"
layout="@layout/layoutcase1" />
<include
android:id="@+id/include02"
layout="@layout/layoutcase2" />
<include
android:id="@+id/include03"
layout="@layout/layoutcase3" />
</LinearLayout>
// Faced with complex layout structures, nested applications are necessary ~
The problem of screen rotation : (Landscape: horizontal screen Portrait : vertical screen )
// Get the current device orientation state
this.getResources().getConfiguration().orientation == Configuration.ORIENTATION_PORTRAIT
Three states of the device:
Configuration.ORIENTATION_PORTRAIT // Constant, the device is in portrait state
Configuration.ORIENTATION_LANDSCAPE // Constant, the device is in landscape state
Configuration.ORIENTATION_UNDEFINED // Constant, the device is in an unknown state
Note: setContentView () in Activity can reload the layout file.