webview支持返回

app/src/main/java/com/example/informationkanban/MainActivity.java

@@ -209,13 +209,26 @@ public class MainActivity extends AppCompatActivity {
     }
 
     @Override
-    public void onBackPressed() {
-        if (System.currentTimeMillis() - clickTime > 2000) {
-            Toast.makeText(MainActivity.this, "再按一次退出", Toast.LENGTH_SHORT).show();
-        } else {
-            super.onBackPressed();
+    public boolean onKeyDown(int keyCode, KeyEvent event) {
+        if (keyCode == KeyEvent.KEYCODE_BACK) {
+            if (webView != null && webView.canGoBack()) {
+                webView.goBack();
+                return true;
+            }
+
+            long currentTime = System.currentTimeMillis();
+            // 3秒内连按两次后退按钮，退出应用
+            if (currentTime - clickTime < 3000) {
+                finish();
+            } else {
+                Toast.makeText(getApplicationContext(), "再按一次返回键退出", Toast.LENGTH_SHORT).show();
+                clickTime = currentTime;
+            }
+
+            return true;
         }
-        clickTime = System.currentTimeMillis();
+
+        return super.onKeyDown(keyCode, event);
     }
 
     /**