Android

Question

我有一个 Fragment 和一个 ListView。当我单击此列表中的某个元素时，我想在 Snackbar 中显示被单击元素的标题，但出现错误。我该如何解决？

分段方法：

mListViewSongs.setOnItemClickListener(new AdapterView.OnItemClickListener() {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        View rowView = view;
        TextView tv = (TextView) rowView.findViewById(R.id.song_title);
        Song selectedSong = (Song) mListViewSongs.getItemAtPosition(position);
        String title = "▶ "+selectedSong.getSongName();
        mainActivity.setSelectedSong(title);
    }
});

Activity里面使用的方法：

public void setSelectedSong(String title) {
    Snackbar snack = Snackbar.make(coordinatorLayout, title, Snackbar.LENGTH_SHORT);
    View viewSnack = snack.getView();
    TextView txtv = (TextView) viewSnack.findViewById(android.support.design.R.id.snackbar_text);
    txtv.setGravity(Gravity.CENTER_HORIZONTAL);
    snack.show();
}

此外，我测试了将文本居中对齐的 Snackbar 方法，但它不起作用，为什么？

日志：

FATAL EXCEPTION: main
Process: com.sebbsoft.app, PID: 2080
Theme: themes:{}
java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.view.ViewGroup.getContext()' on a null object reference
at android.support.design.widget.Snackbar.<init>(Snackbar.java:183)
at android.support.design.widget.Snackbar.make(Snackbar.java:215)
at com.sebbsoft.app.PlayActivity.setSelectedSong(PlayActivity.java:354)
at com.sebbsoft.app.Fragments.TracksListFragment.onItemClick(TracksListFragment.java:133)
at android.widget.AdapterView.performItemClick(AdapterView.java:310)
at android.widget.AbsListView.performItemClick(AbsListView.java:1145)
at android.widget.AbsListView$PerformClick.run(AbsListView.java:3066)
at android.widget.AbsListView.run(AbsListView.java:3903)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5461)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Answer 1

您可以直接在片段中显示 Snackbar 而不是调用 activity 的方法。直接在 onItemClick() 中要显示 Snackbar -

的地方试试这个

Snackbar snack = Snackbar.make(android.R.id.content, title, Snackbar.LENGTH_SHORT);
View viewSnack = snack.getView();
TextView txtv = (TextView) viewSnack.findViewById(android.support.design.R.id.snackbar_text);
txtv.setGravity(Gravity.CENTER_HORIZONTAL);
snack.show();

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