Android _ teach you how to write jump games (2)

This is the second blog. In this tutorial, We will write a small ball.

First, let's take a look at the class diagrams of the small ball class:

 

 

Mainly determine the coordinates of the ball: x, y. Radius of the ball: r. And the motion function of the ball and the draw () function on the screen.

Difficulty: move () function. We will simulate a physical environment to make the ball look elastic. For details about this part, I will answer it in the next article.

The code for Ball. java is given below.

[Java] package jumpball. game;
 
Import android. graphics. Canvas;
Import android. graphics. Color;
Import android. graphics. Paint;
 
Public class Ball {
Float r, x, y;
Private Paint mPaint;
// The maximum vertical speed direction is up to 16.
Float MAXVERTICALSPEED =-16, MAXVERTICALA = 1;
// Default maximum height
Float defaultJumpHight;
// The distance to move the ball in the vertical direction!
Float verticalMove;
Float ha = 0, va = 1f, v0v, vtv, v0h, vth;
GameView gameView;
 
Public Ball (GameView gameView ){
This. gameView = gameView;
MPaint = new Paint ();
MPaint. setColor (Color. BLACK );
DefaultJumpHight = gameView. height/3;
R = gameView. width/36;
Y = gameView. height-r * 2;
X = gameView. width/2-r;
// Calculated based on the acceleration formula Vt ^ 2-V0 ^ 2 = 2AX
MAXVERTICALSPEED =-(int) (float) Math. sqrt (2 * gameView. height/3)-1 );
VerticalMove = defajumjumphight;
V0v = MAXVERTICALSPEED;
}
 
Public void draw (Canvas canvas ){
Move ();
Canvas. drawCircle (x, y, r, mPaint );
}
 
Public void move (){
// Vt = V0 + aT current speed = initial speed + acceleration * Time
Vtv = v0v + va;
// When the descent speed reaches a certain degree, set the acceleration to 0.4f.
If (vtv>-5 * MAXVERTICALSPEED/8 ){
Va = 0.4f;
} Else {
Va = MAXVERTICALA;
}
// When the current height to be increased is greater than the default height, the speed continues to maintain the maximum speed, vtv <0 indicates the direction up
If (verticalMove> defaultJumpHight & vtv <0 ){
Vtv = MAXVERTICALSPEED;
}
Float vMove = (v0v + vtv)/2; // This time the vertical height is moved.
VerticalMove = verticalMove + vMove; // reduces the number of hours, indicating that the Internet has moved
Y = y + vMove;
V0v = vtv;
If (y> gameView. height) {// touched the ground
Y = gameView. height-this. r;
V0v = MAXVERTICALSPEED;
VerticalMove = defajumjumphight;
}
}
}
Package jumpball. game;

Import android. graphics. Canvas;
Import android. graphics. Color;
Import android. graphics. Paint;

Public class Ball {
Float r, x, y;
Private Paint mPaint;
// The maximum vertical speed direction is up to 16.
Float MAXVERTICALSPEED =-16, MAXVERTICALA = 1;
// Default maximum height
Float defaultJumpHight;
// The distance to move the ball in the vertical direction!
Float verticalMove;
Float ha = 0, va = 1f, v0v, vtv, v0h, vth;
GameView gameView;

Public Ball (GameView gameView ){
This. gameView = gameView;
MPaint = new Paint ();
MPaint. setColor (Color. BLACK );
DefaultJumpHight = gameView. height/3;
R = gameView. width/36;
Y = gameView. height-r * 2;
X = gameView. width/2-r;
// Calculated based on the acceleration formula Vt ^ 2-V0 ^ 2 = 2AX
MAXVERTICALSPEED =-(int) (float) Math. sqrt (2 * gameView. height/3)-1 );
VerticalMove = defajumjumphight;
V0v = MAXVERTICALSPEED;
}

Public void draw (Canvas canvas ){
Move ();
Canvas. drawCircle (x, y, r, mPaint );
}

Public void move (){
// Vt = V0 + aT current speed = initial speed + acceleration * Time
Vtv = v0v + va;
// When the descent speed reaches a certain degree, set the acceleration to 0.4f.
If (vtv>-5 * MAXVERTICALSPEED/8 ){
Va = 0.4f;
} Else {
Va = MAXVERTICALA;
}
// When the current height to be increased is greater than the default height, the speed continues to maintain the maximum speed, vtv <0 indicates the direction up
If (verticalMove> defaultJumpHight & vtv <0 ){
Vtv = MAXVERTICALSPEED;
}
Float vMove = (v0v + vtv)/2; // This time the vertical height is moved.
VerticalMove = verticalMove + vMove; // reduces the number of hours, indicating that the Internet has moved
Y = y + vMove;
V0v = vtv;
If (y> gameView. height) {// touched the ground
Y = gameView. height-this. r;
V0v = MAXVERTICALSPEED;
VerticalMove = defajumjumphight;
}
}
}
 
Define a small ball object in the GameVIew class.

[Java] Ball ball;
Ball ball;
Instantiate the GameView constructor.

[Html] ball = new Ball (this );
Ball = new Ball (this );
Add the following in the mDraw function of GameView:

[Html] ball. draw (mCanvas );
Ball. draw (mCanvas );
In this way, we have completed the ball object... Wahaha ~ (The game looks a little better !)

Run the program. We can see an elastic ball ~~~~

 

Finally, we move the left and right sides of the ball. This part is relatively simple ~~~

Two boolean variables are defined in GameView to indicate whether the left and right keys are pressed.

Rewrite two methods at the same time

[Html] public boolean onKeyDown (int keyCode, KeyEvent event ){
If (keyCode = KeyEvent. KEYCODE_BACK ){
GameActivity. finish ();
Return true;
} Else if (keyCode = KeyEvent. KEYCODE_DPAD_LEFT ){
LeftKeyDown = true;
} Else if (keyCode = KeyEvent. KEYCODE_DPAD_RIGHT ){
RightKeyDown = true;
}
Return true;
}
Public boolean onKeyUp (int keyCode, KeyEvent event ){
If (keyCode = KeyEvent. KEYCODE_DPAD_LEFT ){
LeftKeyDown = false;
} Else if (keyCode = KeyEvent. KEYCODE_DPAD_RIGHT ){
RightKeyDown = false;
}
Return true;
}
Public boolean onKeyDown (int keyCode, KeyEvent event ){
If (keyCode = KeyEvent. KEYCODE_BACK ){
GameActivity. finish ();
Return true;
} Else if (keyCode = KeyEvent. KEYCODE_DPAD_LEFT ){
LeftKeyDown = true;
} Else if (keyCode = KeyEvent. KEYCODE_DPAD_RIGHT ){
RightKeyDown = true;
}
Return true;
}
Public boolean onKeyUp (int keyCode, KeyEvent event ){
If (keyCode = KeyEvent. KEYCODE_DPAD_LEFT ){
LeftKeyDown = false;
} Else if (keyCode = KeyEvent. KEYCODE_DPAD_RIGHT ){
RightKeyDown = false;
}
Return true;
}
Then add the following in the move method of the ball:

[Html] // horizontal movement settings
If (gameView. leftKeyDown = true ){
Xx = X-10;
}
If (gameView. rightKeyDown = true ){
Xx = x + 10;
}
If (x <r ){
X = r;
}
If (x> gameView. width-r ){
X = gameView. width-r;
}
// Horizontal movement settings
If (gameView. leftKeyDown = true ){
X = X-10;
}
If (gameView. rightKeyDown = true ){
X = x + 10;
}
If (x <r ){
X = r;
}
If (x> gameView. width-r ){
X = gameView. width-r;
}
The left and right movements of the ball have been completed here, but the actual operation has found that the ball cannot be moved at all ~~~

I checked the information and found the problem here:

For a custom View, the onKeyDown method is called only after the focus is obtained ~ The onKeyDown method of Activty is called only when all empty controls are not processed.

Therefore, we add a sentence in the composition method of GameView:

[Html] setFocusable (true );
SetFocusable (true );
Okay... Success ~~~~ In this way, we can control the movement of the ball !!!

For more information about the move function, see the video ~~~

The following shows how to run the program: and a structure of the project:

 

 

For the source code, see the final version!

 

From the EaSy Column