java - 错误：不兼容的类型：SnekEngine 无法转换为 Context

Question

在遵循在线指南之后，我正在 android studios 中构建一个蛇游戏，现在我试图通过在你死后再次玩游戏后添加一个“弹出”框来添加它，但我遇到了一个问题。

我的 AlertDialog 出现错误，

AlertDialog.Builder alert = new AlertDialog.Builder( this );

我被告知

error: incompatible types: SnekEngine cannot be converted to Context

并且错误指向this.

这是整个班级，给我带来麻烦的位在底部。

package com.example.snek;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.res.AssetFileDescriptor;
import android.graphics.Point;
import android.media.AudioManager;
import android.media.SoundPool;
import android.os.Bundle;
import android.view.Gravity;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import java.io.IOException;
import java.util.Random;
import android.content.res.AssetManager;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.view.View;
import android.widget.Button;
import android.widget.LinearLayout;
import android.widget.PopupWindow;
import android.widget.TextView;

public class SnekEngine extends SurfaceView implements Runnable
{
    // Our game thread for the main game loop
    private Thread thread = null;

    // To hold a reference to the Activity
    private Context context;

    // for playing sound effects
    private SoundPool soundPool;
    private int eat_food = -1;
    private int snake_crash = -1;

    // For tracking movement Heading
    public enum Heading {UP, RIGHT, DOWN, LEFT}
    // Start by heading to the right
    private Heading heading = Heading.RIGHT;

    // To hold the screen size in pixels
    private int screenX;
    private int screenY;

    // How long is the snake
    private int snakeLength;

    // Where is Food hiding?
    private int foodX;
    private int foodY;

    // The size in pixels of a snake segment
    private int blockSize;

    // The size in segments of the playable area
    private final int NUM_BLOCKS_WIDE = 40;
    private int numBlocksHigh;

    // Control pausing between updates
    private long nextFrameTime;
    // Update the game 10 times per second
    private final long FPS = 10;
    // There are 1000 milliseconds in a second
    private final long MILLIS_PER_SECOND = 1000;
// We will draw the frame much more often

    // How many points does the player have
    private int score;
    private int highscore;

    // The location in the grid of all the segments
    private int[] snakeXs;
    private int[] snakeYs;

    // Everything we need for drawing
// Is the game currently playing?
    private volatile boolean isPlaying;

    // A canvas for our paint
    private Canvas canvas;

    // Required to use canvas
    private SurfaceHolder surfaceHolder;

    // Some paint for our canvas
    private Paint snekcolor;
    private Paint textcolor;
    private Paint foodcolor;


    public SnekEngine(Context context, Point size) {

        super(context);

        context = context;

        screenX = size.x;
        screenY = size.y;

        // Work out how many pixels each block is
        blockSize = screenX / NUM_BLOCKS_WIDE;
        // How many blocks of the same size will fit into the height
        numBlocksHigh = screenY / blockSize;

        // Set the sound up
        soundPool = new SoundPool(10, AudioManager.STREAM_MUSIC, 0);
        try {
            // Create objects of the 2 required classes
            // Use m_Context because this is a reference to the Activity
            AssetManager assetManager = context.getAssets();
            AssetFileDescriptor descriptor;

            // Prepare the two sounds in memory
            descriptor = assetManager.openFd("get_mouse_sound.ogg");
            eat_food = soundPool.load(descriptor, 0);

            descriptor = assetManager.openFd("death_sound.ogg");
            snake_crash = soundPool.load(descriptor, 0);

        } catch (IOException e) {
            // Error
        }


        // Initialize the drawing objects
        surfaceHolder = getHolder();
        snekcolor = new Paint();
        textcolor = new Paint();
        foodcolor = new Paint();

        // If you score 200 you are rewarded with a crash achievement!
        snakeXs = new int[200];
        snakeYs = new int[200];

        // Start the game
        newGame();

    }

    @Override
    public void run() {

        while (isPlaying) {

            // Update 10 times a second
            if(updateRequired()) {
                update();
                draw();
            }

        }
    }

    public void pause() {
        isPlaying = false;
        try {
            thread.join();
        } catch (InterruptedException e) {
            // Error
        }
    }

    public void resume() {
        isPlaying = true;
        thread = new Thread(this);
        thread.start();
    }

    public void newGame() {
        // Start with a single snake segment
        snakeLength = 1;
        snakeXs[0] = NUM_BLOCKS_WIDE / 2;
        snakeYs[0] = numBlocksHigh / 2;

        // Get Food ready for dinner
        spawnFood();

        // Setting the high score
        if (score > highscore)
            highscore = score;

        // Reset the score
        score = 0;

        // Setup nextFrameTime so an update is triggered
        nextFrameTime = System.currentTimeMillis();
    }


    public void spawnFood() {
        Random random = new Random();
        foodX = random.nextInt(NUM_BLOCKS_WIDE - 1) + 1;
        foodY = random.nextInt(numBlocksHigh - 1) + 1;
    }

    private void eatFood(){
        //  Got him!
        // Increase the size of the snake
        snakeLength++;
        //replace Bob
        // This reminds me of Edge of Tomorrow. Oneday Bob will be ready!
        spawnFood();

        //add to the score
        score = score + 1;

        // Setting the high score
        if (score > highscore)
            highscore = score;

        soundPool.play(eat_food, 1, 1, 0, 0, 1);
    }

    private void moveSnake(){
        // Move the body
        for (int i = snakeLength; i > 0; i--) {
            // Start at the back and move it
            // to the position of the segment in front of it
            snakeXs[i] = snakeXs[i - 1];
            snakeYs[i] = snakeYs[i - 1];

            // Exclude the head because
            // the head has nothing in front of it
        }

        // Move the head in the appropriate heading
        switch (heading) {
            case UP:
                snakeYs[0]--;
                break;

            case RIGHT:
                snakeXs[0]++;
                break;

            case DOWN:
                snakeYs[0]++;
                break;

            case LEFT:
                snakeXs[0]--;
                break;
        }
    }

    private boolean detectDeath(){
        // Has the snake died?
        boolean dead = false;

        // Hit the screen edge
        if (snakeXs[0] == -1) dead = true;
        if (snakeXs[0] >= NUM_BLOCKS_WIDE) dead = true;
        if (snakeYs[0] == -1) dead = true;
        if (snakeYs[0] == numBlocksHigh) dead = true;

        // Eaten itself?
        for (int i = snakeLength - 1; i > 0; i--) {
            if ((i > 4) && (snakeXs[0] == snakeXs[i]) && (snakeYs[0] == snakeYs[i])) {
                dead = true;
            }
        }

        return dead;
    }

    public void update() {
        // Did the head of the snake eat Food?
        if (snakeXs[0] == foodX && snakeYs[0] == foodY) {
            eatFood();
        }

        moveSnake();

        if (detectDeath()) {
            //start again
            soundPool.play(snake_crash, 1, 1, 0, 0, 1);

            newGame();
        }
    }

    public void draw() {
        // Get a lock on the canvas
        if (surfaceHolder.getSurface().isValid()) {
            canvas = surfaceHolder.lockCanvas();

            // Fill the screen with Game Code School blue
            canvas.drawColor(Color.argb(255, 0, 0, 0));

            // Set the color of the paint to draw the snake white
            textcolor.setColor(Color.argb(255, 153, 255, 153));

            snekcolor.setColor(Color.argb(255, 153, 255, 153));

            // Scale the HUD text
            textcolor.setTextSize(90);
            canvas.drawText("High Score:" + highscore, 10, 70, textcolor);
            canvas.drawText("Score:" + score, 10, 150, textcolor);

            // Draw the snake one block at a time
            for (int i = 0; i < snakeLength; i++) {
                canvas.drawRect(snakeXs[i] * blockSize,
                        (snakeYs[i] * blockSize),
                        (snakeXs[i] * blockSize) + blockSize,
                        (snakeYs[i] * blockSize) + blockSize,
                        snekcolor);
            }

            // Set the color of the paint to draw Food red
            foodcolor.setColor(Color.argb(255, 0, 255, 255));

            // Draw Food
            canvas.drawRect(foodX * blockSize,
                    (foodY * blockSize),
                    (foodX * blockSize) + blockSize,
                    (foodY * blockSize) + blockSize,
                    foodcolor);

            // Unlock the canvas and reveal the graphics for this frame
            surfaceHolder.unlockCanvasAndPost(canvas);
        }
    }

    public boolean updateRequired() {

        // Are we due to update the frame
        if(nextFrameTime <= System.currentTimeMillis()){
            // Tenth of a second has passed

            // Setup when the next update will be triggered
            nextFrameTime =System.currentTimeMillis() + MILLIS_PER_SECOND / FPS;

            // Return true so that the update and draw
            // functions are executed
            return true;
        }

        return false;
    }

    @Override
    public boolean onTouchEvent(MotionEvent motionEvent) {

        switch (motionEvent.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_UP:
                if (motionEvent.getX() >= screenX / 2) {
                    switch(heading){
                        case UP:
                            heading = Heading.RIGHT;
                            break;
                        case RIGHT:
                            heading = Heading.DOWN;
                            break;
                        case DOWN:
                            heading = Heading.LEFT;
                            break;
                        case LEFT:
                            heading = Heading.UP;
                            break;
                    }
                } else {
                    switch(heading){
                        case UP:
                            heading = Heading.LEFT;
                            break;
                        case LEFT:
                            heading = Heading.DOWN;
                            break;
                        case DOWN:
                            heading = Heading.RIGHT;
                            break;
                        case RIGHT:
                            heading = Heading.UP;
                            break;
                    }
                }
        }
        return true;
    }

    public void showNewGameDialog()
    {
        AlertDialog.Builder alert = new AlertDialog.Builder( this );
        alert.setTitle( "This is fun" );
        alert.setMessage( "Play again?" );
        PlayDialog playAgain = new PlayDialog();
        alert.setPositiveButton( "YES", playAgain );
        alert.setNegativeButton( "No", playAgain );
        alert.show();
    }

    private class PlayDialog implements DialogInterface.OnClickListener
    {
        public void onClick( DialogInterface dialog, int id)
        {
            if ( id == -1 ) // yes button
            {
                newGame();
            }

            else if ( id == -2 ) //no button
                //figure out how to exit game.
        }
    }
}

标签： javaandroid

Answer 1

而不是this使用context

AlertDialog.Builder alert = new AlertDialog.Builder( context );