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java - 如何添加下拉菜单

转载 作者:行者123 更新时间:2023-11-30 00:14:30 25 4
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我在这段代码中得到了一个空指针异常。我正在尝试将微调器/下拉菜单添加到屏幕的白色区域。违规代码是:

package dev.android.gamex;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.os.Handler;
import android.support.v4.view.MotionEventCompat;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;
import android.view.Window;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class MainActivity extends AppCompatActivity {
CatchGame cg;
public TextView textView;
public LinearLayout mainLayout;
private Spinner spinner1, spinner2;


// add items into spinner dynamically
public void addItemsOnSpinner2() {

}

// start app
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mainLayout = new LinearLayout(this);
mainLayout.setOrientation(LinearLayout.VERTICAL);

LinearLayout menuLayout = new LinearLayout(this);
menuLayout.setBackgroundColor(Color.parseColor("#FFFFFF"));

textView = new TextView(this);
textView.setVisibility(View.VISIBLE);
String str = "Score: 0";
textView.setText(str);
menuLayout.addView(textView);

Button button = new Button(this);
button.setText("Pause");
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
togglePausePlay();
}
});
menuLayout.addView(button);


// addItemsOnSpinner2();

spinner2 = (Spinner) findViewById(R.id.spinner2);
List<String> list = new ArrayList<String>();
list.add("list 1");
list.add("list 2");
list.add("list 3");
ArrayAdapter<String> dataAdapter = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, list);
dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner2.setAdapter(dataAdapter);

menuLayout.addView(spinner2);


mainLayout.addView(menuLayout);

cg = new CatchGame(this, 5, "Jamie", onScoreListener);
cg.setBackground(getResources().getDrawable(R.drawable.bg_land_mdpi));
mainLayout.addView(cg);
getWindow().requestFeature(Window.FEATURE_ACTION_BAR);
getSupportActionBar().hide();
setContentView(mainLayout);
}

private void togglePausePlay() {
if (cg.paused) {
// play
// getSupportActionBar().hide();
Toast.makeText(MainActivity.this, "Play", Toast.LENGTH_SHORT).show();
} else {
// pause
// getSupportActionBar().show();
Toast.makeText(MainActivity.this, "Pause", Toast.LENGTH_SHORT).show();
}

cg.paused = !cg.paused;
}

private OnScoreListener onScoreListener = new OnScoreListener() {
@Override
public void onScore(int score) {
textView.setText("Score: " + score);
}
};

@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main_menu, menu);
return true;
}

// method called when top right menu is tapped
@Override
public boolean onOptionsItemSelected(MenuItem item) {
super.onOptionsItemSelected(item);
int difficulty = cg.NBRSTEPS;
String name = cg.heroName;

switch (item.getItemId()) {
case R.id.item11:
cg = new CatchGame(this, 3, name, onScoreListener);
setContentView(cg);
mainLayout.addView(cg);
getWindow().requestFeature(Window.FEATURE_ACTION_BAR);
getSupportActionBar().hide();
setContentView(mainLayout);
return true;
case R.id.item12:
cg = new CatchGame(this, 5, name, onScoreListener);
setContentView(cg);
mainLayout.addView(cg);
getWindow().requestFeature(Window.FEATURE_ACTION_BAR);
getSupportActionBar().hide();
setContentView(mainLayout);
return true;
case R.id.item13:
cg = new CatchGame(this, 7, name, onScoreListener);
setContentView(cg);
mainLayout.addView(cg);
getWindow().requestFeature(Window.FEATURE_ACTION_BAR);
getSupportActionBar().hide();
setContentView(mainLayout);
return true;
case R.id.item14:
cg = new CatchGame(this, 9, name, onScoreListener);
setContentView(cg);
mainLayout.addView(cg);
getWindow().requestFeature(Window.FEATURE_ACTION_BAR);
getSupportActionBar().hide();
setContentView(mainLayout);
return true;
case R.id.item15:
cg = new CatchGame(this, 11, name, onScoreListener);
setContentView(cg);
mainLayout.addView(cg);
getWindow().requestFeature(Window.FEATURE_ACTION_BAR);
getSupportActionBar().hide();
setContentView(mainLayout);
return true;
case R.id.item21:
cg = new CatchGame(this, difficulty, "Jamie", onScoreListener);
setContentView(cg);
mainLayout.addView(cg);
getWindow().requestFeature(Window.FEATURE_ACTION_BAR);
getSupportActionBar().hide();
setContentView(mainLayout);
return true;
case R.id.item22:
cg = new CatchGame(this, difficulty, "Spaceship", onScoreListener);
setContentView(cg);
//mainLayout.addView(cg);
//getWindow().requestFeature(Window.FEATURE_ACTION_BAR);
getSupportActionBar().hide();
//setContentView(mainLayout);
return true;
default:
cg.paused = true;
return super.onOptionsItemSelected(item);
}
}

}

interface OnScoreListener {
void onScore(int score);
}

class CatchGame extends View {
int NBRSTEPS; // number of discrete positions in the x-dimension; must be uneven
String heroName;
int screenW;
int screenH;
int[] x; // x-coordinates for falling objects
int[] y; // y-coordinates for falling objects
int[] hero_positions; // x-coordinates for hero
Random random = new Random();
int ballW; // width of each falling object
int ballH; // height of ditto
float dY; //vertical speed
Bitmap falling, hero, jamie2, jamieleft, jamieright;
int heroXCoord;
int heroYCoord;
int xsteps;
int score;
int offset;
boolean gameOver; // default value is false
boolean toastDisplayed;
boolean paused = false;

OnScoreListener onScoreListener;

// constructor, load images and get sizes
public CatchGame(Context context, int difficulty, String name, OnScoreListener onScoreListener) {
super(context);
NBRSTEPS = difficulty;
heroName = name;
this.onScoreListener = onScoreListener;

x = new int[NBRSTEPS];
y = new int[NBRSTEPS];
hero_positions = new int[NBRSTEPS];
int resourceIdFalling = 0;
int resourceIdHero = 0;
if (heroName.equals("Jamie")) {
resourceIdFalling = R.mipmap.falling_object2;
resourceIdHero = R.drawable.left_side_hdpi;
setBackground(getResources().getDrawable(R.mipmap.background));
}
if (heroName.equals("Spaceship")) {
resourceIdFalling = R.mipmap.falling_object;
resourceIdHero = R.mipmap.ufo;
setBackground(getResources().getDrawable(R.mipmap.space));
}
falling = BitmapFactory.decodeResource(getResources(), resourceIdFalling); //load a falling image
hero = BitmapFactory.decodeResource(getResources(), resourceIdHero); //load a hero image
jamieleft = BitmapFactory.decodeResource(getResources(), R.drawable.left_side_hdpi); //load a hero image
jamieright = BitmapFactory.decodeResource(getResources(), R.drawable.right_side_hdpi); //load a hero image

ballW = falling.getWidth();
ballH = falling.getHeight();
}

public CatchGame(Context context, int difficulty, String name, OnScoreListener onScoreListener, Drawable background) {
this(context, difficulty, name, onScoreListener);
this.setBackground(background);
}

// set coordinates, etc.
void initialize() {
if (!gameOver) { // run only once, when the game is first started
int maxOffset = (NBRSTEPS - 1) / 2;
for (int i = 0; i < x.length; i++) {
int origin = (screenW / 2) + xsteps * (i - maxOffset);
x[i] = origin - (ballW / 2);
hero_positions[i] = origin - hero.getWidth();
}
int heroWidth = hero.getWidth();
int heroHeight = hero.getHeight();

hero = Bitmap.createScaledBitmap(hero, heroWidth * 2, heroHeight * 2, true);
hero = Bitmap.createScaledBitmap(hero, heroWidth * 2, heroHeight * 2, true);
jamieleft = Bitmap.createScaledBitmap(jamieleft, jamieleft.getWidth()* 2, jamieright.getWidth() * 2, true);
jamieright = Bitmap.createScaledBitmap(jamieright, jamieright.getWidth()* 2, jamieright.getWidth() * 2, true);

heroYCoord = screenH - 2 * heroHeight; // bottom of screen

}
for (int i = 0; i < y.length; i++) {
y[i] = -random.nextInt(1000); // place items randomly in vertical direction
}

offset = (NBRSTEPS - 1) / 2; // place hero at centre of the screen
heroXCoord = hero_positions[offset];

// initialize or reset global attributes
dY = 2.0f;
score = 0;
gameOver = false;
toastDisplayed = false;
}

// method called when the screen opens
@Override
public void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
screenW = w;
screenH = h;
xsteps = w / NBRSTEPS;
initialize();
}

// method called when the "game over" toast has finished displaying
void restart(Canvas canvas) {

toastDisplayed = true;
initialize();
draw(canvas);
}

// update the canvas in order to display the game action
@Override
public void onDraw(Canvas canvas) {
if (toastDisplayed) {
restart(canvas);
return;
}
super.onDraw(canvas);

int heroHeight = hero.getHeight();
int heroWidth = hero.getWidth();
int heroCentre = heroXCoord + heroWidth / 2;

Context context = this.getContext();

// compute locations of falling objects
for (int i = 0; i < y.length; i++) {
if (!paused) {
y[i] += (int) dY;
}
// if falling object hits bottom of screen
if (y[i] > (screenH - ballH) && !gameOver) {
dY = 0;
gameOver = true;
paused = true;
int duration = Toast.LENGTH_SHORT;

final Toast toast = Toast.makeText(context, "GAME OVER!\nScore: " + score, duration);
toast.show();
Handler handler = new Handler();
handler.postDelayed(new Runnable() {
@Override
public void run() {
toast.cancel();
toastDisplayed = true;
}
}, 3000);
//Vibrator v = (Vibrator) context.getSystemService(context.VIBRATOR_SERVICE);
// Vibrate for 3000 milliseconds
//v.vibrate(3000);

}
// if the hero catches a falling object
if (x[i] < heroCentre && x[i] + ballW > heroCentre &&
y[i] > screenH - ballH - heroHeight) {

y[i] = -random.nextInt(1000); // reset to new vertical position
score += 1;
onScoreListener.onScore(score);
}

}

canvas.save(); //Save the position of the canvas.

for (int i = 0; i < y.length; i++) {
canvas.drawBitmap(falling, x[i], y[i], null); //Draw the falling on the canvas.
}
canvas.drawBitmap(hero, heroXCoord, heroYCoord, null); //Draw the hero on the canvas.

canvas.restore();
//Call the next frame.
invalidate();
}

// event listener for when the user touches the screen
@Override
public boolean onTouchEvent(MotionEvent event) {
if (paused) {
paused = false;
}
int action = MotionEventCompat.getActionMasked(event);
if (action != MotionEvent.ACTION_DOWN || gameOver) { // non-touchdown event or gameover
return true; // do nothing
}
int coordX = (int) event.getX();
int xCentre = (screenW / 2) - (hero.getWidth() / 2);
int maxOffset = hero_positions.length - 1; // can't move outside right edge of screen
int minOffset = 0; // ditto left edge of screen

if (coordX < xCentre && offset > minOffset) { // touch event left of the centre of screen
offset--; // move hero to the left

if(coordX < heroXCoord)// + heroWidth / 2)
hero = Bitmap.createScaledBitmap(jamieleft, jamieleft.getWidth() , jamieleft.getHeight() , true);

}
if (coordX > xCentre && offset < maxOffset) { // touch event right of the centre of screen
offset++; // move hero to the right

if(coordX > heroXCoord)
hero = Bitmap.createScaledBitmap(jamieright, jamieright.getWidth() , jamieright.getHeight() , true);

}
heroXCoord = hero_positions[offset];

return true;
}
}

痕迹:

 main
Process: dev.game.adventure, PID: 5294
java.lang.RuntimeException: Unable to start activity ComponentInfo{dev.game.adventure/dev.android.gamex.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Spinner.setAdapter(android.widget.SpinnerAdapter)' on a null object reference
at dev.android.gamex.MainActivity.onCreate(MainActivity.java:78)
at android.app.Activity.performCreate(Activity.java:6975)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892) 
at android.app.ActivityThread.-wrap11(Unknown Source:0) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593) 
at android.os.Handler.dispatchMessage(Handler.java:105) 
at android.os.Looper.loop(Looper.java:164) 
at android.app.ActivityThread.main(ActivityThread.java:6541) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767) 

存储库是 available online.

我的 XML 是

<?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:paddingLeft="16dp"
android:paddingRight="16dp"
android:orientation="vertical" >

<Spinner android:id="@+id/Spinner01"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />

</LinearLayout>

我的布局应该是这样的。下拉菜单应该出现在暂停按钮的右侧。

enter image description here

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