从 class 获取 Intent 值并将 Intent 设置为另一个 class

Question

大家好，有人可以帮我解决这个过程吗？我只是想在一个按钮上测试这个。假设：

点击btnEasy1后，会进入ButtonFunctionsclass，对GameActivityclass进行必要的设置。

PS。我暂时只在一个按钮（btnEasy1）上尝试这个 PPS。该错误表明我正在尝试对空对象引用调用虚拟方法。

ImageButton btnEasy1, btnEasy2, btnEasy3, btnEasy4, btnEasy5, btnEasy6, btnEasy7, btnEasy8, btnEasy9, btnEasy10, btnBack;
    int row = 0 , column = 0 , stage = 0;
    ButtonFunctions btnFunc;

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

        this.btnEasy1 = findViewById(R.id.btnEasy1);
        this.btnEasy2 = findViewById(R.id.btnEasy2);
        this.btnEasy3 = findViewById(R.id.btnEasy3);
        this.btnEasy4 = findViewById(R.id.btnEasy4);
        this.btnEasy5 = findViewById(R.id.btnEasy5);
        this.btnEasy6 = findViewById(R.id.btnEasy6);
        this.btnEasy7 = findViewById(R.id.btnEasy7);
        this.btnEasy8 = findViewById(R.id.btnEasy8);
        this.btnEasy9 = findViewById(R.id.btnEasy9);
        this.btnEasy10 = findViewById(R.id.btnEasy10);
        this.btnBack = findViewById(R.id.btnBack);

        //Easy Level intents
        Intent easyLevelIntent = new Intent(getApplicationContext(), GameActivity.class);

        btnBack.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(getApplicationContext(), Level_Selection.class);
                startActivity(intent);
                finish();
            }
        });

        btnEasy1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                btnFunc =new ButtonFunctions();
                btnFunc.functions("easy1");
                finish();
            }
        });

public class ButtonFunctions extends AppCompatActivity {

    int row, column, stage;

    public void functions(String diffStage){
        Intent easyLevelIntent = new Intent(getApplicationContext(), GameActivity.class);

        if(diffStage.equals("easy1")){
            stage = 1 ;row = 2; column = 2 ;
            setRowCol(easyLevelIntent);
            startActivity(easyLevelIntent);
        }
    }
    private void setRowCol(Intent easyLevelIntent) {
        easyLevelIntent.putExtra("easyStageCount", stage);
        easyLevelIntent.putExtra("rowCount", row);
        easyLevelIntent.putExtra("colCount", column);
        easyLevelIntent.putExtra("difficulty", 1);
    }

    Process: com.flip, PID: 10543
    java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
        at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:106)
        at com.flip.Functions.ButtonFunctions.functions(ButtonFunctions.java:14)
        at com.flip.StageSelection.Level_Easy.onClick(Level_Easy.java:54)
        at android.view.View.performClick(View.java:5680)
        at android.view.View$PerformClick.run(View.java:22650)
        at android.os.Handler.handleCallback(Handler.java:836)
        at android.os.Handler.dispatchMessage(Handler.java:103)
        at android.os.Looper.loop(Looper.java:203)
        at android.app.ActivityThread.main(ActivityThread.java:6364)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1076)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:937)

Answer 1

您已将 ButtonFunctions 声明为扩展 AppCompatActivity。但是这个 class 不是 Activity，它只是一个实用程序 class。您收到此 NullPointerException 是因为您使用 new 关键字创建了 Activity。这是不允许的。只有 Android 框架可以正确创建 Android 组件（Activity, Service, Provider）的新实例。

您应该从 ButtonFunctions class 声明中删除 extends AppCompatActivity 并向任何需要参数的方法添加 Context 参数。比如这个：

public void functions(Context context, String diffStage){
    Intent easyLevelIntent = new Intent(context, GameActivity.class);

    if(diffStage.equals("easy1")){
        stage = 1 ;row = 2; column = 2 ;
        setRowCol(easyLevelIntent);
        context.startActivity(easyLevelIntent);
    }
}

另一种方法是将所有方法从 ButtonFunctions 移动到您的 Activity，因为它们似乎非常依赖它。但这是您需要做出的架构选择。

从 class 获取 Intent 值并将 Intent 设置为另一个 class

Getting Intent values from a class and set Intent to another class

java

oop

android

android-intent

android-fragments