将 activity 放入收藏夹页面时出错

Question

我有一个矢量可绘制图像。它的用途是，无论何时单击它，activity 都会被添加到收藏夹页面。

这是我的 kinematics.java class

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_kinematics);
    Toolbar toolbar = (Toolbar) findViewById(R.id.phy_lawtoolbar);
    setSupportActionBar(toolbar);
    setTitle(R.string.Kinematics);
    drawerLayout = (DrawerLayout) findViewById(R.id.phy_draw);
    navigationView = (NavigationView) findViewById(R.id.nav_view_phy);
    phy_law_toggel = new ActionBarDrawerToggle(this, drawerLayout, R.string.open, R.string.Close);
    drawerLayout.addDrawerListener(phy_law_toggel);
    toolbar = (Toolbar) findViewById(R.id.phy_lawtoolbar);
    setSupportActionBar(toolbar);
    phy_law_toggel.syncState();
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    navigationView.setItemIconTintList(null);
    webView = (WebView) findViewById(R.id.phy_law_web);
    fav = (ImageButton) findViewById(R.id.fav);
    webView.getSettings().setJavaScriptEnabled(true);
    webView.getSettings().setBuiltInZoomControls(true);
    webView.getSettings().setSupportZoom(true);
    webView.getSettings().setDisplayZoomControls(true);
    webView.loadUrl("file:///android_asset/mathscribe/Kinematics.html");

    final ArrayList<String> mfavlist = new ArrayList<String>();
    final Favouritepage favr = new Favouritepage();
    kine = this.getClass().getSimpleName();
    fab = (FloatingActionButton) findViewById(R.id.fab);
    final ArrayList<String> resultArray = getIntent().getStringArrayListExtra("mfavlist");

    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            webView.scrollTo(0, 0);
        }
    });

    fav.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            resultArray.add(kine);
            }
    });


    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        if (phy_law_toggel.onOptionsItemSelected(item)) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

favouritepage.java

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_favouritepage);

    ArrayList<String> mfavlist = new ArrayList<String>();

    Intent intent = new Intent(Favouritepage.this,Favouritepage.class);
    intent.putExtra(" mfavlist ", mfavlist);
    startActivity(intent);
}

每当我点击 vectordrawable 图标时，应用程序就会崩溃并显示 NullPointerException 错误

这是我的崩溃日志

AndroidRuntime: FATAL EXCEPTION: main Process: com.example.alpit.formula2, PID: 2991 java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.ArrayList.add(java.lang.Object)' on a null object reference at com.example.alpit.formula2.Kinematics.onClick(Kinematics.java:71) at android.view.View.performClick(View.java:4802) at android.view.View$PerformClick.run(View.java:20102) at android.os.Handler.handleCallback(Handler.java:810) at android.os.Handler.dispatchMessage(Handler.java:99) at android.os.Looper.loop(Looper.java:189) at android.app.ActivityThread.main(ActivityThread.java:5529) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:950) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:745)

Answer 1

两件事：

首先删除 favoritepage.java

也用putStringArrayListExtra代替putExtra

intent.putStringArrayListExtra("mfavlist", mfavlist);

编辑 1

您还可以考虑在创建 Intent:

时实际指定 other activity

Intent intent = new Intent(Favouritepage.this, Kinematics.class);

将 activity 放入收藏夹页面时出错

Error while putting activity inside the favourite page

android

nullpointerexception

android-vectordrawable