设置按钮在android中的Textwatcher中可见/不可见

Question

当用户在Edittext上添加任何单词时，我想显示一个隐藏按钮。 我已经尝试过这种方法：

((Button)findViewById(R.id.btnClear)).setVisibility(View.VISIBLE);

这是我在TextWatcher中的代码：

final EditText txtSearch = (EditText)findViewById(R.id.txtSearch);
txtSearch.addTextChangedListener(new TextWatcher() {
    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {

    }

    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {
        ((Button)findViewById(R.id.btnClear)).setVisibility(View.VISIBLE);
        CategoryCustomAdapter adapter2 =
                new CategoryCustomAdapter(showCategoryListActivity.this,
                        DatabaseHelper.getCategories(
                                showCategoryListActivity.this,s.toString()));
        ((ListView)findViewById(R.id.lstCategorylist)).setAdapter(adapter2);
    }

    @Override
    public void afterTextChanged(Editable s) {

    }
});

除了这一行，每件事情都很好：

((Button)findViewById(R.id.btnClear)).setVisibility(View.VISIBLE);

我相信你可以帮助我。 ps：API 19 Nexus 4 android 4.4.2

Answer 1

如前所述声明你变量-in Oncreate。

Button howtoButton = (Button) view.findViewById(R.id.howtobutton);

比这样使用

howtoButton.setVisibility(View.VISIBLE)
howtoButton.setVisibility(View.GONE)

Answer 2

终于明白了。
日志说：

  

android.support.v7.widget.AppCompat ImageButton 无法强制转换为   android.widget。按钮

在onCreate（）上更改此内容：

final Button btnClear = (Button)findViewById(R.id.btnClear);

到此：

final ImageButton btnClear = (ImageButton)findViewById(R.id.btnClear);

我不知道为什么但是我使用了一些背景作为我的Button以及一些如何转向 ImageButton 和btnClear.setVisibility(View.VISIBLE);在public void onTextChanged(CharSequence s, int start, int before, int count)中正常工作

public class showCategoryListActivity extends AppCompatActivity {

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

        final ListView lstCategory = (ListView) findViewById(R.id.lstCategorylist);
        final ImageButton btnClear = (ImageButton)findViewById(R.id.btnClear);
        final EditText txtSearch = (EditText)findViewById(R.id.txtSearch);

        CategoryCustomAdapter adapter =
                new CategoryCustomAdapter(this,DatabaseHelper.getCategories(
                        this,((TextView)findViewById(R.id.txtSearch)).getText().toString()));
        lstCategory.setAdapter(adapter);

        txtSearch.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                btnClear.setVisibility(View.VISIBLE);
                CategoryCustomAdapter adapter2 =
                        new CategoryCustomAdapter(showCategoryListActivity.this,
                                DatabaseHelper.getCategories(
                                        showCategoryListActivity.this,s.toString()));
                ((ListView)findViewById(R.id.lstCategorylist)).setAdapter(adapter2);
            }

            @Override
            public void afterTextChanged(Editable s) {

            }
        });
        txtSearch.setOnEditorActionListener(new TextView.OnEditorActionListener() {
            @Override
            public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
                if (actionId == EditorInfo.IME_ACTION_SEARCH) {
                    CategoryCustomAdapter adapter = new CategoryCustomAdapter(
                            showCategoryListActivity.this,
                            DatabaseHelper.getCategories(
                                    showCategoryListActivity.this,
                                    ((TextView)findViewById(R.id.txtSearch)).getText().toString()));
                    ((ListView)findViewById(R.id.lstCategorylist)).setAdapter(adapter);
                    return true;
                }
                return false;
            }
            });
    }


    public void btn_clear_clicked(View view) {
        ((TextView)findViewById(R.id.txtSearch)).setText("");
        CategoryCustomAdapter adapter = new CategoryCustomAdapter(
                showCategoryListActivity.this,
                DatabaseHelper.getCategories(
                        showCategoryListActivity.this,
                        ((TextView)findViewById(R.id.txtSearch)).getText().toString()
                )
        );
        ((ListView)findViewById(R.id.lstCategorylist)).setAdapter(adapter);
    }

}

按钮的XML：

＆＃13;

＆＃13;

    <ImageButton
        android:id="@+id/btnClear"
        android:layout_width="25dp"
        android:layout_height="25dp"
        android:text="Button"
        android:layout_marginLeft="5dp"
        android:layout_marginRight="5dp"
        android:background="@android:drawable/ic_menu_close_clear_cancel"
        android:layout_marginTop="11dp"
        android:layout_alignParentTop="true"
        android:layout_alignParentEnd="true"
        android:onClick="btn_clear_clicked (showCategoryListActivity)"
        android:visibility="invisible"
        android:elevation="0dp" />

＆＃13;

＆＃13;

＆＃13;

对不起我的粗心